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Microbiology of frozen food
Introduction to the subject
(Microbiology of Frozen Foods)
It is widely assumed that frozen foods do not pose a microbiological threat to consumers and, in general, this confidence is justified. Nevertheless (in spite of this), success does not depend on the fact that the initial foodstuffs are of a sound hygiene quality before freezing, and, furthermore, that the thawing/cooking operations reflects the properties of the frozen product. The achievements of these twin aims; without adverse effect on the organoleptic characteristics of the food, has been the essential aim of the manufacturers of frozen foods, and the increased usages of home freezers is a tribute to their success.
Some of the problems associated with the freezing of different commodities, together with the techniques for overcoming them, are to be discussed thoroughly in this subject, and if this knowledge will help to further the safety of frozen foods, then its collation (all together) will have been fully justified.
Normal flora of fish:
Outline
* Background
* Microbiology of fish
* Eggs, skin, gills microflora
* Intestinal microflora
* Diseases (pathogens)
Background:
The flora of living fish depends on the microbial content of the waters in which they live. The slime of fish contains species of Pseudomonas, Acinetobacter, Moraxella, Alcaligenes, Micrococcus, Flavobacterium, Corynebacterium, Saracia, Vibrio, and Bacillus. Fish from northern waters are mostly contains psychrophiles, but fish from tropical waters carry more mesophiles. Freshwater fish carry freshwater bacteria, e.g. species of Aeromonas, Lactobacillus, Brevibacterium, Alcaligenes, and Streptococcus.
In the intestines of fish from both sources contain species of Alcaligenes, Pseudomonas, Flavobacterium, Vibrio, Bacillus, Clostridium, and Escherichia.
Boats, boxes, bins, fish houses, and fishers soon become heavily contaminated with those bacteria and transfer them to the fish during cleaning.
Slime and the skin of newly caught ocean fish showed bacterial counts 102 to several million/cm2, and the intestinal fluid may contain from 103 to 108 /mm2. Gill tissue give shelter for 103 to 106/g. Washing reduces the surface count.
Oysters and other shellfish pick up soil and water microorganisms including pathogens, e.g. species of Alcaligenes, Flavobacterium, Moraxella, Acinetobacter, and some Gram-positive bacteria.
Shrimps, crabs, lobsters, and similar seafood have a bacteria-loaded slime on their surfaces that species of Bacillus, Micrococcus, Pseudomonas, Acinetobacter, Moraxella, Flavobacterium, Alcaligenes, and Proteus.
The numbers of microorganisms on the skin of fish can be influenced by the method of catching. For example, trawling fish nets kept at the bottom for long periods results bacteria of sediment in fish.
Natural microflora of mussels and oysters
A majority of isolates are Gram-negative (68%) and aerobic (76%) bacteria. Predominant microflora are species of Vibrio, Pseudomonas, Shewanella, Aeromonas, Acinetobacter, and Flavobacterium.
Amongst Gram-positive bacteria species of Staphylococcus, Bacillus, and Streptococcus are predominant organisms.
Predominant Vibrio species include V. alginolyticus, V. splendidus, and V. (Listonella) anguillarum.
Eggs microflora
Fish embryos secret inorganic and low molecular weight organic compound, which can diffuse out through the shells that attract bacteria for utilizing these compounds and colonize egg surface. Normal healthy eggs include microflora such as Species of Cytophaga and , Pseudomonas. But dead eggs showed fluorescent Pseudomonas spp., which do not involve in causing of dead, but rather attracting to nutrient leaching. Overgrown of bacteria can hamper eggs development., as for e.g. Leucothrix mucor on cod eggs and Flavobacterium ovolyticus on halibut eggs.
Skin Microflora
Skin microflora reflect that of surrounding water, which may have bacterial counts from 102 to 104 / cm2, for examples Gram negative bactewria: Species of Pseudomonas, Moraxella, Vibrio, Flavobacterium, Acinetobacter, and Aeromonas. Gram positive: Species of Micrococcus, and Bacillus.
Gill Microflora
Gill microflora may contain 102 to 106 bacteria/ g of fish and form extensive colonization of certain types of bacteria (e.g. Flavobacterium spp.). Other common examples are Gram negative: Species of Pseudomonas, Flavobacterium, Vibrio, Moraxella, Cytophaga and Gram positive: Species of Micrococcus, and Bacillus (in warmer water).
Intestinal microflora
Intestinal microflora have been established at the larval stage. These are developed into a persistent flora at the juvenile stage.
Population of microorganisms in fish tends to increase along the length of the gestrointestinal tract. Largest number of bacteria in the intestines (up to 108 CFU/g) includes Gram negative: Pseudomonas spp., Vibrio spp., Achromobacter spp., Flavobacterium spp., Corynebacterium spp., Aeromonas spp. and Gram positive: Bacillus spp., Micrococcus spp. Vibrio dominates in seawater and Aeromonas dominates in freshwater.
Development of the intestinal microbiology
At the time of hatching, the digestive tract of most fish species is an undifferentiated straight tube. Prior to first feeding, microbiology reflects that of the rearing environment. Once feeding begins, microbiology is derived from live feed ingested rather than water.
As the digestive tract becomes more developed, the intestinal microbiology becomes more stable and more complex for the followings:
pH change (lower)
O2 tension (more anaerobic)
Receptors for bacteria
Criteria for testing whether or not microorganism is indigenous to the intestinal tract of fish:
* are found associated with the epithelial
mucosal in the stomach,
* small found in healthy individuals
* colonize early stages and persist throughout
life
* are found in both free-living and hatchery-
cultured fish
* can grow anaerobically in intestine or large
intestine
Roles of intestinal microflora
Accumulate nutrition such as Polyunsaturated fatty acids, amino acids and vitamins. Produce extracellular enzymes: chitinase. Preventing infection from fish pathogens. Competitive attachment. Neutralization of toxins, and Bacteriocidal activity.
Survival and growth:
Bacterial load impacts on survival & digestive organ development. Presence of certain species influence survival of intestinal microflora.
Stimulation of the immune system:
Provide antigens to trigger development of immune responses in the gut
Pathogenesis
Pathogenesis = the origin and development of a disease
Pathogenicity = the ability of a parasite to inflict damage on the host
Entry of the pathogen into the host:
Exposure to pathogens
Adherence to skin or mucosal surface
Invasion through epithelium
Colonization and growth:
Localization (boil, ulcer, etc)
Systematic infection
Production of virulence factors:
Tissue damage via toxins or invasiveness
Types of pathogens
Obligate pathogens: Cause disease in healthy organisms and cause Contagious disease.
Aeromonas salmonicida: Causes Salmonids and other fishes (Furunculosis, skin lesions).
Opportunistic pathogens
Found in the environment
Do not cause disease unless the host immune response is suppressed (stress, environmental factor, etc)
Listonella anguillarum (Fish, mollusks, shrimp, crabs)
Vibriosis
Selective Questions
- (a) Write down the introduction to Microbiology of frozen
foods.
(b) Describe briefly the background of normal flora of fish.
2. (a) Write down natural microflora of mussels and oysters.
(b) illustrate the activity of bacteria on mucosal surface.
3. Write an essay on microflora of skin, gills, and eggs of fish.
4. (a) What are the intestinal microflora of fish?
(b) Give an account of the development of intestinal
microflora and roles of intestinal microflora in fish.
5. (a) Give an outline of pathogenesis and describe its major
steps.
(b) Categorize fish pathogens.
Factors affecting the types and loads of microflora in fish include: Part-1
* Bacterial flora on different parts of live fish,
* Types of fish
* Effect of the environment:
Temperature
Tropical vs temperate water and/or warm water vs cold
water;
• Place (fresh water vs marine water),
Part-2
*Water quality (Clean vs polluted water),
* Seasonal variation,
* Media for culturing,
* Chemicals:
Ammonia, Oxygen, Toxic materials, Pesticides,
insecticides and herbicides
Bacterial flora on different parts of live fish:
Microorganisms are found on skin and gills and in the intestines of live and newly caught fish. The total number of organisms vary enormously ranged from 102 to 107 cfu cm-2 on the skin surface. The gills and the intestines both contain between 103 and 109 cfu g-1. Photobacterium phosphoreum normally surface flora can also be isolated in high numbers from the intestinal tract of some fish species.
The microflora in the slime of fish depends on the species of fish. Liston (1955, 1956) found markedly different bacterial loads on the skin, and gills of skate (a kind of ray-fish) when compared with sole caught in the same place at the same time.
The flora on the skin and gills may derive largely from the surrounding water, or from the bottom mud. Anaerobes e.g. Clostridium spp. are usually absent in slime and gills, but are always present in the gut. Clostridium botulinum naturally occurs in the marine environment. The pychrophilic types E, F and non-proteolytic B contaminate fish from localities.
Clostridium botulinum type E, involved in outbreaks of botulism and can grow at temperatures as low as 3.3°C. This type of organism could cause problems in aquaculture systems, especially in natural earth ponds.
Types of fish:
Indian shark showed no Pseudomonas even though it is largely present in the sea water. Remarkable variations have been observed between flatfish versus round fish, or cartilaginous fish versus bony fish. However, significant differences were found between similar hake caught on the
Gram-positive organisms as Bacillus, Micrococcus, Clostridium, Lactobacillus and coryneforms can also be found in varying proportions, but in general, Gram-negative bacteria dominate the microflora in water.
In tropical warmer waters, higher numbers of mesophiles can be isolated. Gram-positive Bacillus and Micrococcus dominate on fish from tropical waters. However, this conclusion has later been challenged by several studies which have found that the microflora on tropical fish species is very similar to the flora on temperate species. Species of Pseudomonas, Acinetobacter, Moraxella and Vibrio has been found on newly-caught fish in several Indian studies.
The microflora on tropical fish often carries a slightly higher load of Gram-positives and enteric bacteria but otherwise is similar to the flora on temperate-water fish.
Tropical species caught in water around 20 to 25°C tend to have largely mesophilic floras, which able to grow at 34-37°C. Counts as high as 106-107 g-1 have been obtained on shrimp directly out of the nets of trawlers in
Deep water mollusks such as scallops or queens usually have lower counts of E. coli (103 to 106 g-1 at 20°C) than those of estuarine species, e.g. oysters, cockles or mussels (103-108 cm-3).
The main groups of bacteria of crustacean shellfish are coryneforms, Species of Micrococcus, Achromobacter and Pseudomonas, Flavobacterium/Cytophaga and Bacillus. Cold-water shellfish include largely Pseudomonas and Achromobacter, while warmer waters include Micrococcus and coryneforms e.g. Indian prawns. Gulf shrimp contained largely Achromobacter, Micrococcus, Pseudomonas and Bacillus.
Place (Fresh vs marine water):
Aeromonas sp. is typical of freshwater fish, as well as typical of marine waters. These include species of Vibrio, Photobacterium and Shewanella. However, although Shewanella putrefaciens is
characterized as sodium-requiring; it can also be isolated from freshwater environment.
Marine fish from cold or temperate waters have been found to have skin counts at 20°C of 101-107 cm-2, gill counts of 103-107 g-1 and gut content counts of 103-108 cm-3.
Higher figures have been reported for Indian sardine (30-37°C). While 37°C counts give lower recoveries than 20°C counts for cold-water fish. For cold-water fish, counts at 0oC are almost as high as for 20°C. The microflora on the skin and gill surfaces of cold-water marine species consists largely of Gram-negative rods e.g. species of Pseudomonas, Moraxella and Acinetobacter, Flavnbacterium and Vibrio. The microflora on warm-water marine fish,
consists mainly Gram-positive bacteria e.g. Micrococcus, Corynebacteriurn, Brevibacterium and Bacillus in varying proportions.
Freshwater fish tend to have lower counts than marine species, viz. 102 to 105 cm-2 for skin and 101 to107 g-1 or ml-1 for gut content of temperate fish, and 103 to 105 cm-2 and 104 to 106 g-1 or ml-1 for skin and guts of tropical species.
The microflora of freshwater fish includes most salt-water genera, including Aeromonas, Lactobacillus, Alkaligenes, Streptococcus and Enterobacteriaceae. Warm-water fish often have large numbers of coryneforms and Salmonella
Freshwater, immature fish had 100% terrestrial bacteria in the gut, while transplant fish in 50% sea
water had a 49/51% ratio of terrestrial to marine types. Freshwater fish are contaminated by faecal organisms and pathogens than marine fish. Higher contamination of fish was recorded during caught in areas close to sewage outfalls or other polluted streams.
In
Selective questions:
- Write down the bacterial flora on different parts
of live fish.
2.Elucidate the effect of the environment on
microflora of fish.
3.What are the microflora in fresh water and marine water fish?
Seasonal variation:
Evidence suggests that bacterial loads on skin slime and gills of fish show seasonal variations linked with changes in environment.
Skate (a ray fish), and cod (Sea-fish, a source of cod liver oil) showed two peaks, in late spring and autumn, following on plankton blooms. On the other hand, a three-year study of the skin flora of hake (a kind of cod fish) caught within a 15-hour fishing, showing considerable variations in both numbers and types of microorganisms.
For example-1, the dominant genus found on freshly caught hake (Sea-fish, related to cod fish) in 15 out of the 17 catches examined in one study was Pseudomonas, whereas a few years previously Achromobacter spp. was found to predominate. The major genus in cod has been variously quoted as Pseudomonas, Achromobacter, or Micrococcus. Some examples are given below.
Example-2:
A study on seasonal quantitative and qualitative analyses of the bacterial flora associated with the intestine of hybrid tilapia cultured in earthen ponds in Saudi Arabia showed total viable counts (cfu g-1) of bacteria in the intestine varied between 6.8±1.9×106 to 7.5±1.4×107 in early summer, 1.6±2.0×106 to 5.1±2.5×107 in summer, 3.1±1.4×108 to 1.3±2.2×109 in autumn, and 8.9±1.8×105 to 1.3±0.9×107 in winter. Altogether, 17 bacterial genera were identified from the intestine of tilapia. The bacteria were predominantly Gram-negative rods (77%). Aeromonas hydrophila, Shewanella putrefaciens, Corynebacterium urealyticum, Escherichia coli and Vibrio cholerae were the most abundant species with a prevalence of >10% in most cases except V. cholerae. Considerable numbers of Pseudomonas spp. were found only in winter. Photobacterium damselae, and species of Pasteurella, Cellulomonus and Bacillus were present in some seasons of the year.
Example-3:
The seasonal bacterial flora of fish ponds were quantitatively and qualitatively examined atquarterly intervals for one year from April 2001 to March 2002 for the first time in Saudi Arabia showing total viable count (cfu ml-1) of bacteria in pond water ranged from 7.8±0.9 x 103 to 1.3±1.1 x 104 in Summer (33.0±2.3oC); 5.1±1.7 x 103 to 2.2±1.0 x 104 in Fall (24.1±1.9oC); and 6.7±2.1 x 102 to 2.5±0.6 x 103 in Winter (14.5 ±1.5oC). In total, 21 different species of bacteria from 19 different genera were isolated. The predominant microflora consisted of Gram-negative rods.
Aeromonas hydrophila, Shewanella putrefaciens, Corynebacterium urealyticum, and Escherichia coli were the most prevalent bacteria in all seasons. Species of Flavobacterium and Pseudomonas were dominant only in the winterPasteurella spp. were also consistently isolated throughout the sampling period. Bacteria present seasonally were species of Pseudomonas, Flavobacterium, Cellulomonus, and Micrococcus. Ambient seasonal temperature variation could account for some of the bacterial population variation. Presence of fecal coliform bacteria in the fish-culture waters suggests that care should be practiced during processing the fish caught from these waters to prevent contamination of edible meat.
Example-4:
Seasonal variation in the number of halophilic histamine-forming bacteria on/in marine fish and changes in their number on marine fish stored at25oC were studied. Psychrophilic halophilic histamine forming bacteria were detected from viscera and skin of fish throughout one year. Besides these mesophilic halophilic histamine-forming bacteria were isolated from mackerel during May and July, and from horse mackerel (a sea fish) in June, July, September, and November. The occurrence of these bacteria showed similar seasonal variations to that in sea water reported earlier by the same group of investigators. During storage of mackerel at 25oC, both types of halophilic histamine- forming bacteria increased in the fish muscle, they could be detected at a cell count of 101 to 103 g-1 after 16 h of storage. Histamine concentration in the muscle after 24 h increased to become 70-120 mg g-100. This suggested that these new mesophilic halophilic histamine-formers were responsible for the scombroid poisoning.
Medium:
The numbers and types of bacteria recovered can also be influenced by the medium used and the incubation temperature. There was a debate whether marine bacteria are really psychrophilic or even truly marine. Zobell (1946) expressed that marine bacteria are not psychrophiles because their range of optimum growth temperatures is between 18°C and 22°C. But Jay (1978) defined that marine bacteria are psychrophiles capable of growing at temperatures
between 0°C and 7°C.
Many marine microorganisms will grow readily at -3°C and some strains will grow as low as -7.5°C. They can survive almost indefinitely at -3°C to 5°C, though many of them die rapidly at 37°C. Marine bacteria grow better on sea-water-based (SWB) media than on those based on fresh tap water.
More recent studies have suggested that there is little difference in the counts obtained whether or not sea water is used in the media. The proportions of the different genera are, however, affected by the medium used.
Cape hake stored in ice, showed no significant difference was found between total counts in SWB medium or in distilled water based (DWB) medium with 0.5% sodium chloride, at either 37°C or 20°C. Incubation temperature at 37°C showed higher counts in SWB medium than the other. But the counts in SWB medium at 20°C were from 10 to over 80 times greater than those at 37°C. The proportions of the different genera recovered were affected by both the incubation temperature and the medium used. Whereas, Micrococcus was more prolific at 37°C and Bacillus was recovered only at 37°C. Flavobacterium was recovered in small numbers, only in DWB medium at 37°C. This probably reflects the general scarcity of Flavo-bacterium as a component of the microflora of
Growth of Achromobacter, Pseudomonas and Corynebacterium was greater at 20°C, while Micrococcus and Brevibacterium were more prolific at 25°C. The preference of Achromobacter and Pseudomonas for lower temperature, or their relatively greater ability to grow in the cold than other organisms is noted at 0°C and even lower.
Water quality (Clean and polluted water):
Water quality is one of the primary factors affecting the spread of parasites and diseases. Many abnormal behaviors exhibited by fish can be attributed to poor water quality.
Upon determining that the fish has a problem, the first thing to suspect is to be water quality.
It is generally accepted that the flesh of freshly caught healthy fish is sterile. The skin and gills, however, may carry high loads of bacteria.
In polluted waters, high numbers of Enterobacteriaceae may be found. In clean temperate waters, these organisms disappear rapidly, but it has been shown that Escherichia coli and Salmonella can survive for very long periods in tropical waters and once introduced may almost become indigenous to the environment (Table 1).
Table 1. Bacterial flora on fish caught in clean, unpolluted
waters
| Gram-negative | Gram-positive |
| Pseudomonas | Bacillus |
| Moraxella | Clostridium |
| Acinetobacter | Micrococcus |
| Shewanella putrefaciens | Lactobacillus |
| Flavobacterium | Coryneforms |
| Cytophaga | |
| Vibrio, | |
Japanese studies have shown very high numbers of microorganisms in the gastrointestinal tract of fish than in the surrounding water.
Mollusks caught in unpolluted waters probably have floras similar to those of crustaceans or fish living in the same area. Certain shellfish, however, when harvested from waters subject to contamination, can become a health hazard. Oysters and other bivalves allow passing of large quantities of water over a filter system during feeding that can carry with them organisms of faecal origin. Mollusks grown in sewage-contaminated water can be dangerous. The large outbreak of food poisoning due to oysters in
Apart from contamination by pollution, shellfish can carry food poisoning organisms of marine origin.
C. botulinum has already been mentioned; another widespread species is V. parahaemolyticus. This organism found on fish or shellfish, has been responsible for about 40% of the incidents of food poisoning in
A further class of microorganism causing food poisoning in filter-feeding shellfish is the dinoflagellates (Gonyaulex and Gymnodinium). These could produce the most potent human toxins. Moulds, yeasts and viruses do not play a large partin the microbiology of fish. Rhodotorula yeasts are occasionally responsible for pink discoloration in oysters.
Food poisoning microbes are rarely found in fish caught in unpolluted waters and spoilage of fish is caused by their naturally occurring microflora. These are generally more or less psychrophilic and are capable of growing down to 0°C and, for some strains, several degrees lower.
Fish caught in very cold, clean waters carry the lower numbers whereas fish caught in warm waters have slightly higher counts. Very high numbers, i.e., 107 cfu cm-2 are found on fish from polluted warm waters.
Chemicals:
Ammonia
75% of the total ammonia present in a pond is from one of the bi-products of fish respiration. Ammonium (NH4), is the ionized form of ammonia. If the pH of the pond water is acid, the ammonium molecule remains intact and non toxic. If the pH of the pond water is alkaline, the ammonium molecule releases one hydrogen ion and becomes ammonia (NH3), the non ionized form. Ammonia is toxic to your fish. The amount of toxicity depends on how alkaline the water is. As pH increases above 7, the amount of ammonium transformed into ammonia is exponentially related to the pH.
Oxygen
Oxygen is needed for the normal day to day functions of a fish and by the bacteria necessary for the breakdown of the fish's waste products in the nitrification process. Factors affecting the amount of oxygen in the water are temperature, fish load, organic load, medications, and the turn over rate. All of these factors affect oxygen inversely except the turn over rate. Minimum levels of oxygen should be 5 PPM.
Toxic Metals
Most natural waters contain chloride, sulfate, carbon, calcium, magnesium, sodium and potassium. These ions serve a vital purpose in the mineral metabolism of all animals. If these ions are found in high concentrations, their toxicity is dependent on water hardness, pH, temperature and the presence of other dissolved substances.
The solubility and toxicity of zinc, lead, aluminum and copper have a direct relationship to increases of pH and water hardness.
Elevated levels of heavy metals can alter the qualitative and quantitative structure of microbial communities.
Pesticides & Insecticides & Herbicides
These are usually introduced into the water by runoff, precipitation or accidental spills, which make water changes. Water contaminated with these chemicals make water adverse for fish breeding resulting reduction of fish.
Use of antibiotics or dip
Antibiotics also have been tried experimentally, usually in a dip or in ice. Of those tested, , pediocin, nicin, natamycin, chlortetracycline and oxytetracycline seemed best, and now their use is permitted. Chloramphenicol is fairly effective, and penicillin, streptomycm, and subtilin are poor or useless.
Selective ouestion:
1.Elucidate seasonal variations of microflora in fish linked with changes in environment. Cite examples. (6.0)
2. The numbers and types of bacteria in fish can also be influenced by the medium used and the incubation temperature. Explain. (6.0)
3. Water quality is one of the primary factors affecting the spread of parasites and diseases in fish. Explain. (6.0)
4. Describe the effect of chemicals on microflora in fish. (3.0)
5. Describe fish-borne diseases and their causative agents.
Industrial Microbiology
Introduction:
Industrial Microbiology is a relatively new science, as is all of microbiology.
Industrial Microbiology deals with all forms of microbiology which have an economic aspect.
It deals with those areas of microbiology on which a monetary value can be placed which involves
a fermentation product or some forms of deterioration,
disease
waste disposal etc.
Industrial microbiology is a very broad area for study.
Use of microbes to obtain a product or service of economic value constitutes industrial microbiology.
Any process mediated by or involving microorganisms in which a product of economic value is obtained is called fermentation.
The terms industrial microbiology and fermentation are virtually synonymous in their scope, objectives and activities.
The microbial product may be microbial cells (living or dead), microbial biomass, and components of microbial cells, intracellular or extracellular enzymes or chemicals produced by the microbes utilizing the medium constituents or the provided substrate.
The activities in industrial microbiology begin with the isolation of microorganisms from nature, their screening for product formation, improvement of product yields, maintenance of cultures, mass culture using bioreactors, and usually end with the recovery of products and their purification.
Industrial Microbiology includes the following areas
Soil and agricultural microbiology
Medical microbiology
Microbial physiology
Cytology and morphology
Virology
Genetics
Marine microbiology
Food and dairy microbiology and
Immunology
Disciplines not related to microbiology are also important in Industrial microbiology, such as-
Organic, inorganic and physical chemistry
Biochemistry
Engineering
Medicine
Economics
Sales and law, particularly patent law.
Studying microbes helps us to understand the world around us:
Microbes are useful tools in research because of their rapid life cycle, their simple growth requirements, and their small size.
Due to this simplicity, microbes have been essential in understanding core questions in biology.
Attempts to classify microorganisms have lead to a classification system that divides all organisms into three domains of life, Archaea, Bacteria, and Eukarya.
Microbes provide tools for use in molecular biology. These tools have allowed scientists to make rapid progress in investigating many types of microorganisms.
Use of microorganisms in Industry:
Industrialist may wish to diversify their overall product line, or they may wish to employ microorganisms to bring about some change in a raw material, by-product, or product normally associated with company’s production activities.
Microorganisms may bring about deterioration or, in some other manner, modify a product in an unwanted manner so that an industrial concern is forced to consider the industrial aspects of microbial activity.
There are many facets to industrial microbiology.
Examples of particular areas of application include the sterilization, deterioration and quality control associated with the production and handling of food and beverage products.
Microorganisms are industrially employed as a means for prospecting for new oil reserves, and for obtaining better oil recovery from present reserves.
Roles of industrial microbiologists:
The industrial microbiologist is interested in ways of combating disease agents of plants, animals, and man.
He/she is concerned with the microbe’s ability to modify a soil environment for the growing of green plants, particularly with the relationships of microorganisms to soil fertility and with the ability of soil microbe to degrade man-made pesticides and other chemicals.
Industrial microbiology concerns itself
with the isolation and description of microorganisms from natural environments and
With the cultural conditions required for obtaining rapid and massive growth of these organisms in the lab and in large scale cultural vessels commonly known as fermentors.
The ability of microorganisms to convert inexpensive raw materials or substrates, to economically valuable organic compounds is of considerable concern to the industrial microbiologist.
Patents and Industrial Microbiology:
Patents are of importance to industrial microbiology in that they provide a certain degree of economic protection to an inventor for a new fermentation process or product.
Thus patents provide the impetus for the expenditure of the huge sums of money often required for the research and development associated with new fermentation processes.
Microbial Products of Potential Importance:
Products Example
1. Amino acids L-glutarnic acid, L-lysine
2. Antibiotics Streptomycin, penicillin, tetracyc1ines, polymyxin
3. Beverages Wine, beer, distilled beverages
4. Biodegradable plastic β-polyhydroxybutyrate
5. Enzymes Amylase, proteases, pectinases, invertase, cellulase
6. Flavouring agents Monosodium glutamate, nucleotides
7. Foods Cheese, pickles, yoghurt, bread, vinegar
8. Gases CO2, H2,CH4
9. Organic acids Lactic, citric, acetic, butyric, fumaric
In studying industrial microbiology, the student should concentrate on the economic aspects of how man makes use of or combats the activities of microorganisms.
But the student must not lose sight of the basic concepts of microbiology which have no immediately apparent money-making possibilities.
Fermentation:
The term fermentation is derived from the Latin verb ferver, to boil, thus describing the appearance of the action of yeast on extracts of fruit or malted grain.
Fermentation is a process of energy production in a cell in an anaerobic environment (with no oxygen present).
In common usage, fermentation is a type of anaerobic respiration, however a more strict definition exists which defines fermentation as respiration in an anaerobic environment with no external electron acceptor.
Fermentation and industrial microbiology:
The production of alcohol by the action of yeast on malt or fruit extracts has been carried out on a large scale for very many years and was the first industrial process for the production of a microbial metabolite.
Thus, industrial microbiologists have extended the term fermentation to describe any process for the production of product by the mass culture of a microorganism.
What Causes Fermentation:
Spoiled wine threatening livelihood of vintners, so they funded research into how to promote production of alcohol, but prevent spoilage by acid during fermentation
Some believed air caused fermentation reactions, while others insisted living organisms caused fermentation
This debate also linked to debate over spontaneous generation.
Pasteur’s Experiments on fermentation
What causes fermentation?
Pasteur’s Experiments on fermentation (contd..)
Pasteur’s Experiments on fermentation (contd..)
Showed that anaerobic bacteria fermented grape juice into acids, which suggested a method for preventing spoilage in wine. To prevent this he developed a technique what came to be known as pasteurization (use of heat to kill contaminating bacteria to reduce spoilage of food and beverages) à industrial microbiology = biotechnology.
Pasteur, due to significant accomplishments working with microbes is considered the Father of Modern Microbiology.
Buchner’s Experiments on Acellular Fermentation
Showed, in 1897, that fermentation does not require the actual presence of living cells, but only cell-produced proteins called enzymes.
Buchner’s work begin the field of biochemistry and the study of metabolism (all chemical reactions within an organism).
Buchner’s (1860 –1917) Experiments on Acellular Fermentation
Industrial microbiology and development of pharmaceutical industry
Industrial microbiology refers primarily to bulk production of organic compounds such as antibiotics, hormones, vitamins, acids, solvents, and enzymes.
Industrial process usually occur on a much larger scale, produce a specific compound, and involve numerous complex stages.
The aim of industrial microbiology is to produce chemicals that can be purified and packaged for sale or for use in other commercial processes. Thousands of tons of organic chemicals worth several billion dollars are produced by this industry every year.
To create just one of these products, an industry must determine which microbes, starting compounds, and growth conditions work best, which requires an investment of 10 to 15 years and billions of dollars for research and development.
The microbes used by fermentation industries have traditionally been naturally occurring (wild) strains of bacteria or molds that carry out a particular action on a substrate.
Industrial microbiologists have several tricks to increase the amount of the chosen end product. First, they can manipulate the growth environment to increase the synthesis of a metabolite.
Another strategy is to select microbial strains that genetically lack a feedback system to regulate the formation of end products, thus encouraging mass accumulation of this product.
From microbial factories to industrial factories
Industrial fermentations begin with microbial cells acting as living factories. When exposed to optimum conditions, they multiply in the trillions and synthesize large volumes of a desired product.
Such mass microbial fermentations are the driving force of industrial microbiology. To produce appropriate levels of growth and fermentation, the microbes must be cultivated in a carefully controlled environment. This process is basically similar to culturing bacteria in a test tube of nutrient broth.
Many commercial fermentation processes have been worked out on a small scale in a lab and then scaled up to a large commercial venture.
An essential component for scale up is a fermentor, a device in which mass cultures are grown, reactions take place, and product develops.
Some fermentors are large tubes, flasks, or vats, but most industrial types are metal cylinders with built-in mechanisms for stirring, cooling, monitoring, and harvesting product.
Fermentors are made of materials that can made of materials that can withstand pressure, and are rustproof, nontoxic, and leak-proof.
For optimum yield, a fermentor must duplicate the actions occurring in a tiny volume (a test tube) on a massive scale.
Most microbes performing fermentations have as aerobic metabolism, and the large volumes make it difficult to provide adequate oxygen.
Fermentors have a built-in device called a sparger that aerates the medium to promote aerobic growth.
To increase the contact between the microbe and the nutrients, paddles located in the central part of the fermentor vigorously stir the fermentation mixture and maintain its uniformity.
The temperature of the chamber is maintained by cooling jacket.
Industrial microbiology and substance production
• The general steps in mass production of organic substances in a fermentor can be summarized as:
1. Introduction of microbes and sterile media into the reaction chamber
2. Fermentation
3. Downstream processing (recovery, purification, and packaging)
4. Removal of waste
Some products come from this process ready to package, whereas others require further purification, extraction, concentration, or drying.
The end product is usually in a power, cake, granular, or liquid form that is placed in sterilized containers.
The waste products can be drained off and can be used in other processes or discarded, and the residential microbes and nutrients from the fermentation chamber can be recycled back into the system or removed for the next run.
Microbial biotechnology
Biotechnology is better defined as process biotechnology. This is simply described as a discipline, which enables its exponents to convert raw materials to final products when either the raw material and/or a stage in the production process involve biological entities.
It involves the conjoint interaction of two identifiable sub-components; bioscience and biotechnology.
It is defined as “The applications of scientific and engineering principles to the processing of material by biological agents to provide goods and services
Microbial enzyme technology
Various microorganisms like bacteria, fungi and protozoa produce different kinds of enzymes. They produce extracellular enzyme to break those organic and inorganic compounds, which have high molecular weight. Simpler substances can easily be assimilated through cell membranes of microorganisms.
Bacillus mesentericus, B. polymyxa, B. macerans produce bacterial amylase and protease. Proteases are used to design cotton and silk.
Commercial production of amylase is carried out by yeast. Yeast also produce invertase. It is used for sweeting in confectionary.
Microbial genetic engineering
Genetic engineering is the most fundamental mechanics of biotechnologies. It involves exchange of genes, as well as the introduction into a cell of a gene belonging to another to bacteria, in particular the through in vitro genetic recombination.
Such technique has been applied to bacteria where genes of animal and human cells have been introduced and propagated.
The genetic recombination consists of an exchange of genes between two chromosomes.
Genetic recombination is the process capable of giving birth to cells or individuals in which two or more hereditary determinants, by which their former parents differed, are associated in new way.
Microbial Products and Processes
Why we use microbes in the industry?
Microorganisms are used to produce useful products for the benefit of mankind.
They are used to increase productivity.
Prerequisites for Using microbes to manufacture products
Microbial products are found from various metabolic reactions of microorganisms.
The overall reaction characterizing the industrial application of microbes can be summarized as follows:
Substrate (raw material) + Microorganisms (chemical factory)
/
New products
The organism:
It must be able to produce appreciable amounts of the products.
It should have relatively stable characteristics and the ability to grow rapidly and vigorously.
It should be nonpathogenic
The medium:
It must be cheap and readily available in large quantities.
Nutrient-containing waste have been found to be utilized practically as substrate. E.g: whey from dairy industry, waste liquors from paper industry.
The product:
An efficient and economic product should be produced.
Large-scale method and efficient recovery system of products should be developed.
Purification of desired end-product must be accomplished, because product is a heterogeneous mixture containing microbial cells, constituents of medium etc.
Fermentation
Fermentation may mean---
Fermentation (biochemistry), the process of energy production in a cell under anaerobic conditions (In a lack of oxygen)
Fermentation (food), the conversion of carbohydrates into alcohols or acids under anaerobic conditions used for making certain foods
Fermentation (wine), the process of fermentation commonly used in winemaking.
Fermentation (tea), the name used in the tea industry for the aerobic treatment of tea leaves to break down and release certain unwanted chemicals
Ethanol fermentation, a form of anaerobic respiration used primarily by yeasts when oxygen is not present in sufficient quantity for normal cellular respiration
Industrial fermentation, the breakdown and re-assembly of biochemicals for industry, often in aerobic growth conditions
The major commercial products of microorganisms
Microbial cells: These may be used as food supplements or immunizing agents, e.g: yeast cells, vaccines etc.
Large or macromolecules: Enzymes synthesized by microorganisms.
Primary metabolic products: These are compounds essential for cell growth, e.g: vitamins.
Secondary metabolic products: These are compounds not required for cell growth, e.g: antibiotics
Classification of microbial products
Based on the intended use of the final products the various industrial processes used to produce these microbial products can be divided into several classes:
1. Production of Pharmaceutical chemicals:
Most prominent in this case are the antibiotics and steroid drugs.
Other substances such as insulin and interferon are now being produced by genetically engineered bacterium.
. Production of commercially valuable chemicals:
This class includes solvents, enzymes and intermediate compounds (e,g. ethanol) for the synthesis of other substrates.
3. Production of Food Supplements:
Mass production of yeasts, bacteria and algae from nutritionally enriched media provides a good source of protein and other organic nutrients useful as food supplements, e.g: bread, yogurt, spirullina etc.
4. Production of alcoholic beverages:
Beer, wine, whisky etc are used as alcoholic beverages.
5. Production of Vaccines:
The whole cell or some part or product of the cell is used for the preparation of vaccines.
6. Production of insecticides:
Microbes are used as pesticides or biocontrolling agents, e.g: Bacillus thuringensis.
7. Application in Mining and Petroleum Industry:
Microbes are used for petroleum recovery and other mining process.
8. Microbial activity for the treatment of waste materials:
All kinds of materials such as leather, textiles, woods, metals etc are subject to deterioration by contamination with degrading microbes.
Metabolic products
The microbes used by fermentation industries have traditionally been naturally occurring strains of bacteria and molds that carry out a particular metabolic action on a substrate.
At an increasing rate, however, these microbes are mutant strains of fungi and bacteria that selectively synthesize large amounts of various metabolic intermediates or metabo
Industrial processes harvested following 2 basic metabolic products:
1. Primary metabolites are produced during the major metabolic pathways and are essential for microbe’s function.
2. Secondary metabolites are by-products of metabolism that may not be critical to the microbe’s function.
Characteristics of Secondary Metabolites
Secondary Metabolites are not essential for growth and reproduction.
The formation of secondary metabolites is extremely dependent on growth conditions, especially on the composition of the medium.
Secondary Metabolites are often produced as a group of closely related compounds. For instance, a single strain of a species of Streptomyces has been found to produce over 30 related but different anthracycline antibiotics.
It is often possible to get dramatic overproduction of Secondary Metabolites, whereas primary metabolites, linked as they are to primary metabolism, usually can not be si
Differences between Primary and Secondary Products
In general, primary products are compounds such as amino acids and organic acids synthesized during the logarithmic phase of microbial growth.
Secondary products are compounds such as vitamins, antibiotics and steroids synthesized during stationary phase
Strategies to increase the amount of the chosen end products
Industrial microbiologists can manipulate the growth environment to increase the synthesis of a metabolite. For e.g: adding lactose to glucose as the fermentation substrate increases the production of penicillin by Penicillium.
They can select microbial strains that genetically lack a feedback system to regulate the formation of end product, thus encouraging mass accumulation
Fermentor
Standards of materials used in sophisticated fermentor design
• All materials coming to contact with the solutions entering the bioreactor or the actual organism culture must be corrosion resistant to prevent trace metal contamination of the process.
• The materials must be non-toxic so that slight dissolution of the material or components does not inhibit culture growth.
• The materials of the bioreactor must withstand repeated sterilization with high pressure stream.
• The bioreactor stirrer system, entry ports and end plates must be sufficiently rigid not to be deformed or broken under mechanical stress.
Visual inspection of the medium and culture is advantageous, transparent materials should be used wherever possible.
The parts of a fermentation process
Regardless of the type of fermentation an established process may be divided into 6 basic parts:
1) The formulation of media to be used in culturing the process organism during the development of the inoculum and in the production fermenter.
2) The sterilization of the medium, fermenters and ancillary equipment.
3) The production of an active, pure culture in sufficient quantity to inoculate the production vessel.
4) The growth of the organism in the production fermenter under optimum conditions for product formation.
5) The extraction of the product and its purification.
The disposal of effluents produced by the process
Batch culture
Fed-batch
Continuous culture
Batch culture
In a batch culture the microbes are inoculated into a fixed volume of medium and as growth takes place nutrients are consumed and products of growth (biomass, metabolites) accumulate.
The nutrient environment within the bioreactor is continuously changing, thus , in turn, enforcing changes to cell metabolism.
Eventually, cell multiplication ceases because of exhaustion or limitation of nutrients and accumulation of toxic excreted waste products.
In industrial usage, batch cultivation has been operated to optimise organism or biomass production then to allow the organism to perform specific biochemical transformation such as end-product formation (e.g: aa, enzymes) or decomposition of substances (sewage treatment).
Prolonging the life in a Batch culture
There are means of Prolonging the life in a Batch culture and thus increasing the yield by various substrate feed methods:
Gradual addition of concentrated components of the nutrient, e.g: carbohydrates, so increasing the volume of the culture (fed-batch)-used for industrial production of baker’s yeast.
Addition of medium to the culture (perfusion) and withdrawal of an equal volume of used free cell-free medium-used in animal cultivation.
Advantages of batch and fed-batch culture techniques in Industry
Products may be required only in relatively small quantities at any given time.
Market needs may be intermittent.
Shelf-life of certain products is short.
High product conc. is required in broth to optimise downstream processing operations.
Some metabolic products are produced only during the stationary phase of the growth cycle.
Instability of some production strains require their regular renewal.
Continuous Culture
The practice of continuous culture gives near-balanced growth with the little fluctuation of nutrients, metabolites, cell numbers and biomass.
This practice depends on fresh medium entering a batch system at the exponential phase with a corresponding withdrawal of medium plus cells,
Continuous methods of cultivation will permit organisms to grow under steady state (unchanging) conditions in which growth occurs at a constant rate and in a constant environment.
In industrial practice continuously operated systems are of limited use and include only single cell protein and ethanol productions and some forms of waste-water treatment processes.
Type of culture Operational characteristics Application
Solid Simple, cheap, selection of colonies from single cell possible, process control limited Maintenance of strains, genetic studies, production of enzymes, composting
Film Various types of bioreactor, trickling filter, rotating disc, packed bed, sponge reactor, rotating tube Waste water treatment, monolayer culture, bacterial leaching, vinegar production
Type of culture Operational characteristics Application
Submerged homogeneous distribution of cells; batch Spontaneous reaction, various types of reactor, continuous stirred tank reactor, air lift, loop. Deep shaft etc. agitation by stirrers, air, liquid process control for physical parameters possible. Standard types of cultivation antibiotics, solvents, acids etc
Fed-batch Simple method for control of regulatory effects, e.g. glucose repression Production of Baker’s yeast
Type of culture Operational characteristics Application
Continuous One-stage homogeneous Proper control of reaction, excellent for kinetic and regulatory studies, higher costs of experiment, problem of aseptic operation, the need for highly trained operators. Few cases of application in industrial scale; production of SCP, waste-water treatment.
Some examples of commercial products used in vaccines for active immunization
Disease Nature of immunizing agent
Tuberculosis Live attenuated cells of Mycobacterium bovis
Measles Live attenuated Rubeola virus
Poliomyelitis Live attenuated strains of poliovirus
Rabies Killed rabies virus
Whooping cough Killed cells of Bordetella pertusis
Typhoid fever Killed cells of Salmonella typhi
Diptheria Toxoid prepared from exotoxin of Corynebacterium diptheriae
Tetanus Toxoid prepared from exotoxin of Clostridium tetani
Meningococcal meningitis Capsular polysaccharides from Neisseria meningitisdis
Some antibiotics produced by microbes
Antibiotic Microorganisms
Amphotericin B Streptomyces nodosus
Bacitracin Bacillus licheniformis
Chlorotetracycline Streptomyces aureofaciens
Kanamycin S kanamyceticus
Nystatin S. noursei
Penicillin Penicillin chrysogenum
Polymixin B Bacillus polymyxa
Some examples of enzymes
Enzymes Source Application
Glucose isomerase Bacillus spp, Streptomyces spp Production of high fructose corn syrup
Lipase Rhizopus spp Use in fat removal
Cellulase Trichoderma reesii Digestive aid
Amylase Many bacteria and fungi Starch digesting agent
Renin Fungi Coagulation of milk to make cheese: Dairy product
Protease Many bacteria and fungi Proteolytic enzyme
Human proteins
Genetic engineering has expanded the roles of microbes in the pharmaceutical industry to produce human proteins.
By using recombinant DNA technology human DNA sequences that code for various proteins can be produced commercially.
Recombinant DNA tech provides a means of producing relatively large amount of human proteins for use as prophylactic drugs and diagnostic reagents.
Examples: insulin, growth hormones, interferons, interleukin-2 etc.
Industrially important microorganisms: Screening and selection of microorganisms for useful products
Industrial microorganisms are organisms which have been selected carefully so that they manufacture one or more specific products.
Even if industrial microbe is one which has been isolated by traditional techniques, it becomes a highly modified organism before it enters large-scale industries.
Industrial microorganisms are metabolic specialists, capable of producing specially and to high yield metabolic products.
Where do Industrial Strains Come from?
The ultimate source of all strains of industrial microorganisms is the natural environment.
But through the years, as large-scale microbial processes have preferred, a number of industrial strains have been deposited in Culture Collections.
There are numbers of culture collections which serve as the repositories of microbial cultures.
Culture collections that supply cultures of Industrial microorganisms
Abbreviation Name Location
ATCC American Type Culture Collection US
CDDA Canadian Department of Agriculture Canada
CIP Collection of Institute Pasteur France
IAM Institute of Applied Microbiology Japan
NCTC National Collection of Type Cultures UK
DSM Deutsche Sammlung von Mikroorganismen Germany
Properties of Industrially Important Microorganisms
A microorganism suitable for industrial use must produce the substance of interest.
The organism must be available in pure culture.
Must be genetically stable.
Must grow in large-scale culture.
It must be possible to maintain cultures of the organism for a long period of time in the lab and in the industrial plant.
The culture should preferably produce spores or some other reproductive cell from so that the organisms can be easily inoculated into large fermentors.
The organism must be capable of growing vigorously after inoculation into seed stage vessel.
It must produce the desired product in a relatively short period of time.
The organism must be able to grow in a relatively inexpensive liquid culture medium obtainable in bulk quantities.
It must be able to produce a desirable product preferably in a single one easily recovered and preferably with the absence of any toxic byproducts.
An industrial organism should not be harmful to humans or economically important animals and plants.
The organism should be preferably capable of protecting itself from contamination.
The most favorable industrial organisms are those of large cell size, since larger cells settle rapidly from a culture or can be easily filtered out with relatively inexpensive filter materials.
An industrial microbe should be amenable to genetic manipulation.
Fungi, yeasts and filamentous bacteria re preferred as industrial microorganism.
The Isolation of Industrially Important Microorganisms
The diversity of microorganisms may be exploited still by searching for strains from the natural environment able to produce products of commercial value.
The first stage is isolation.
Isolation involves obtaining either pure or mixed cultures followed by their assessment to determine which carry out the desired reaction or produce the desired product.
Isolation methods utilizing selection of the desired characteristic
Isolation methods depending on the use of desirable characteristics as selective factors are essentially types of enrichment culture.
Enrichment culture is a technique resulting in an increase in the number of a given organism relative to the number of other types in the original inoculum.
Prior to the culture stage it is often advantageous to subject the environmental source to conditions which favor the survival of the target organisms.
For e.g. air-drying the soil will favor the survival of actinomycetes.
Enrichment Liquid Culture:
Enrichment Liquid Culture is frequently carried out in shake flasks.
The growth of the desired type from a mixed inoculum will result in the modification of the medium and therefore changes the selective force which may allow the growth of other organisms.
The selective force may be re-established by inoculating the enriched culture into identical fresh medium.
Such sub culturing may be repeated several times before the dominant organism is isolated by spreading a small inoculum of the enriched culture onto solid medium.
Enrichment Cultures Using Solidified Media:
Solidified Media have been used for the isolation of certain enzyme producers and these techniques usually involve the use of a selective medium incorporating the substrate of the enzyme which encourages the growth of the producing types.
For e.g. isolation of Bacillus spp producing alkaline protease. Soils of various pHs were used as the initial inoculum and, to a certain extent, the number of producers isolated correlated with alkalinity of soil sample. The soil samples were then pasteurized to destroy vegetative cells and then inoculated into agar media at pH 9-10, containing a dispersion of an insoluble protein. Colonies which produced a clear zone due to the digestion of protein were taken to alkaline protease producers.
Screening procedures For Industrial Microorganisms
Screening procedures may be defined as the use of highly selective procedures to allow the detection and isolation of only those microorganisms of interest from a large microbial population.
Different types of techniques are used for screening procedure depending on the source, microorganisms, products etc.
The aim of the screening is the collection of low No. pf organism from a large No. of sample.
Screening is of two types:
Primary screening
Secondary screening
Primary screening
Primary screening allows the detection and isolation of microbe that posses potentially industrial applications.
The primary screening may have yielded only a very small number that have any real commercial value; because it determines which microbes are able to produce a compound without providing much idea of the production or yield potential for the organisms.
Secondary screening
Following primary screening, a secondary screening procedure is required to further test the capabilities and to gain information about target organisms.
Criteria of Secondary screening
Secondary screening is conducted on agar plates, in flasks or small fermentors containing liquid media or as a combination of these approaches.
Liquid cultures are better than agar plate media.
Secondary screening can be quantitative and qualitative in its approach.
Qualitative approach tells us the spectrum of microbes which is sensitive to a newly discovered antibiotic and quantitative approach tells us the yield of antibiotic.
Secondary screening should yield the types of in formations which are needed in order to evaluate the true potential of a microorganism for industrial usage.
For example, it should determine what types of microorganism are involved and whether they can be classified at least to families or genera.
Secondary screening should determine whether the microbes are actually producing chemical compounds not previously described or alternatively, for fermentation processes that are already known, it should determine whether a more economical process is possible.
It should be reveal whether these are pH, aeration or other chemical requirements associated with particular microorganism, both for the growth of organism and for the formation of chemical products.
Secondary screening should also detect gross genetic instability in microbial culture.
It should show whether certain medium constituents are missing or possibly are toxic to growth of the organism or to its ability to accumulate fermentation products.
It should also show something of the chemical stability of the product and of the products solubility in various organic solvents.
Secondary screening should reveal whether a product resulting from a microbial fermentation occurs in the culture broth in more than one chemical form, and whether it is an optically or biologically active material.
Secondary screening should revel whether microorganism are able to chemically alter or even destroying their own fermentation products.
Molecular Screening Methods
Early screening strategies tended to be empirical, labor intensive and had relatively low success rates.
New screening methods have been developed which are more precisely targeted to identify the desired activity.
The progress in molecular biology, genetics and immunology has contributed extensively to the development of innovative screens.
The major contributions are:
• The provision of test organisms that have increased sensitivities, or resistances, to known agents. For e.g. the use of super-sensitive strains for the detection of β-lactam antibiotics.
• The cloning of genes coding for enzymes or receptors that may be used in inhibitor or binding screens makes such materials more accessible and available in much lager amounts.
• The development of reporter gene assays.
• Molecular probes for particular gene sequences may enable the detection of organisms capable of producing certain product groups.
• The development of immunologically based assays such as ELISA.
The Preservation of Industrially Important Microorganisms
The isolation of a suitable organism for a commercial process may be a long and very expensive procedure.
Thus, preservation techniques have been developed to maintain cultures in a state of ‘suspended animation’ by storing either
at reduced temperature or
in a dehydrated form.
Storage at reduced temperature
Storage on agar slopes:
Cultures grown on agar slopes may be stored at 5°C or -20°C and sub-cultured at approx. 6 monthly intervals.
The time of sub-culture may be extended to 1 yr if the slopes are covered with sterile medicinal grade mineral oil.
Storage Under Liquid Nitrogen:
The metabolic activities of m.o may be reduced by storage at very low temp (-150° to 196° C) which may be achieved using a liquid nitrogen refrigerator.
Storage in a dehydrated form
Dried cultures:
Dried soil cultures have been used widely for culture preservation, particularly for sporulating mycelial microorganism.
Moist, sterile soil may be inoculated with a culture and then allowed to dry at room tempt for approximately 2 weeks.
The dry soil may be stored in a dry atmosphere or preferably in a refrigerator.
Lyophilization:
Lyophilization or freeze drying involves freezing of a culture followed by its drying under vacuum, which results in the sublimation of the cell water.
The technique involves growing the culture to the max stationary phase and resuspending the cells in a protective medium such as milk, serum or sodium glutamate.
A few drops of the suspension are transferred to an ampoule, which is then frozen and subjected to a high vacuum until sublimation is complete, after which the ampoule is sealed.
The ampoules may be stored in a refrigerator and the cells may remain viable for 10 yrs or more.
Strain Improvement
The initial source of an industrial microorganism is the natural environment, but the original isolate is greatly modified in the lab.
As a result of this modification, progressive improvement in the yield of a product can be anticipated.
For e.g. production of penicillin from the fungus Penicillium chrysogenum. When penicillin was 1st produced on a large scale, yields of only 1-10 μg/ml were obtained. Over the yrs, as a result of strain improvement coupled with changes in the medium and growth conditions, the yield of penicillin has been increased to about 50,000 μg/ml!
The introduction of new genetic techniques has led to further yield increases.
The process of strain improvement involves the continual genetic modification of the culture.
Genetic modification may be achieved by selecting natural variants, by selecting recombinants.
Selection of natural variants may be results in increased yields but it is not possible to rely on such improvements, and techniques must be employed to increase the chances of improving the culture.
These techniques are the isolation of induced mutants and recombination.
The most dramatic examples of strain improvement come from the applications of recombinant DNA technology which has resulted in microorganism producing compounds which they were not able to produce previously.
The advances in these techniques have resulted in very significant improvements in the production of conventional fermentation products.
Stages of Strain Improvement
Process for strain improvement comprises of several stages.
Data provided by Customer analysis to plan further research
Strain and Technology parameters required for "start point" determination
Strain mutability evaluation includes period for probationary mutagenesis series when great variety of mutagen factor combinations affects the strain. All data for obtained mutants during this preliminary mutagenesis is considered thoroughly for further stage.
Screening and selection among great deal of mutant varieties is a very demanding stage:
experts' deep knowledge in combination with many years of experience and scientific intuition makes it successful
Induced mutagenesis as the basis of Laboratory Know-How represents combination of classical methods for chemical and physical impact on the strain
Technology parameter optimisation
Process scale-up
Recovery Technology Improvement: under Customer request
Use of Microorganisms in Different Industries: Biocatalysts
The chemical industry:
using biocatalysts to produce novel compounds, reduce waste byproducts and improve chemical purity.
The plastics industry: decreasing the use of petroleum for plastic production by making "green plastics" from renewable crops such as corn or soybeans.
The paper industry:
improving manufacturing processes, including the use of enzymes to lower toxic byproducts from pulp processes.
The textiles industry:
lessening toxic byproducts of fabric dying and finishing processes. Fabric detergents are becoming more effective with the addition of enzymes to their active ingredients.
The food industry: improving baking processes, fermentation-derived preservatives and analysis techniques for food safety.
The livestock industry: adding enzymes to increase nutrient uptake and decrease phosphate byproducts.
The energy industry: using enzymes to manufacture cleaner biofuels from agricultural wastes.
Wednesday, June 10
Tuesday, June 9
medical Microbiology
Epidemiology:
The science that studies when and where diseases occur and how they are transmitted in populations is called epidemiology.
There are three basic types:
1.Descriptive epidemiology:Data about infected people are collected and analyzed.
2.Analytical epidemiology:A group of infected people is compared with an uninfected group.
3.Experimental epidemiology:Controlled experiments designed to test hypotheses
Infectious diseases:
Infectious disease: A disease in which pathogens invade a susceptible host and carry out at least part of their life cycle in the host.
Infectious disease requires an agent and a mode of transmission (or vector). A good example is malaria, which is mainly caused by the parasite Plasmodium falciparum but does not affect humans unless the vector, the Anopheles mosquito, is around to introduce the parasite into the human bloodstream.
In order to cause infectious disease a pathogen must accomplish the following:
– It must enter the host
– It must metabolize and multiply on or in the host tissue
– It must resist host defenses
– It must damage the host
Symptoms:
Changes in the body function such as pain and malaise. These subjective changes are not apparent to an observer.
Signs:
These are objective changes that the physician can observe and measure such as fever, swelling etc.
Syndromes:
A specific group of signs and symptoms always accompanies a particular disease; such a group is called a syndrome.
On the basis of how they behave within a host and within a given population:
Classify infectious diseases:
1.Communicable disease: Any disease that spreads from one host to another, either directly or indirectly, is said to be a communicable disease. e.g.: chickenpox, typhoid. Chickenpox is also an e.g. of contagious disease that easily spread from one to another.
2. Noncommunicable disease: Not spread from one host to another, caused by normal flora of the body or by m.o that reside outside the body produce only when introduce into the body. Clostridium tetani produce disease when it enters into body via wounds.
• Occurrence of disease:
•
• The incidence of a disease is the fraction of a population that contracts it during a particular period.
• The prevalence of a disease is the fraction of the population having the disease at a specified time.
• Frequency of occurrence is another criterion in the classification of disease:
– Sporadic disease: If a particular disease occurs only occasionally, e.g: typhoid fever in a area.
– Endemic disease: A disease constantly present in the population such as common cold.
– Epidemic disease: If many population in a given area acquire a certain disease in a relevantly short period, e.g: influenza and other STD.
– Pandemic disease: A epidemic disease that occurs worldwide , e.g: AIDS may become a pandemic disease.
Severity or duration of disease:
Acute disease:
• That develops rapidly but lasts only a short time, e.g: influenza.
Chronic disease:
• Develops more slowly and body’s reaction may be less severe, but the disease is likely to be continual or recurrent for long periods. Tuberculosis, hepatitis B etc
Subacute disease:
• A disease that is intermediate between acute and chronic. E.g: sclerosing panencephalitis, a rare brain disease characterized by diminished intellectual function and loss of nervous function.
Latent disease:
• In which the causative agent remains inactive for a time but then becomes active to produce symptoms of the disease. e.g:shingles, one of the diseases caused by varicella-zoster virus.
Classification of infections:
( Extent of host Invoivment)
• There are generally two types of infection, local and systemic. There are different, as well as, similar symptoms for each type.
Local Infection:
• A local infection is an infection in which the entire body is not infected, only a specific portion or the portion which is affected. For example an infected wound or cut would be an example of a local infection. Boils and abscesses are local infections. Symptoms of a local infection are indicative to the site and include:
-pain
-redness
-pus
-swelling
-foul odor drainage
-heat to the site
Systemic infection:
• Microorganisms or their products are spread throughout the body by the blood or lymph. Signs and symptoms of a systemic infection include:
-fever
-aches
-chills
-nausea
-vomiting
-weakness
Focal infection:
• Very frequently, agents of a local infection enter a blood or lymph vessel and spread to other specific parts of the body, then the infection is called focal infection.
• Focal infections may arise from infections in the teeth, tonsils or sinuses.
– The presence of bacteria in blood is known as bacteremia.
– If the bacteria multiply in the blood then the condition is called septicemia.
– The presence of virus in blood is known as viremia
– Toxemia refers to presence of toxins in blood.
• The state of host resistance also determines the extent of infections:
– Primary infection: An acute infection that causes initial illness.
– Secondary infection: Caused by opportunistic microbes after the primary infection has weakened the body’s defense. It may become more serious than primary infection e.g. streptococcal bronchopneumonia following influenza.
– Inapparent / subclinical infection: The infection does not cause any noticeable illness. Poliovirus can be carried by people who never develop illness.
Principle of Disease and epidemiology:
The science that studies when and where diseases occur and how they are transmitted in populations is called epidemiology.
There are three basic types:
1.Descriptive epidemiology:Data about infected people are collected and analyzed.
2.Analytical epidemiology:A group of infected people is compared with an uninfected group.
3.Experimental epidemiology:Controlled experiments designed to test hypothese
Patterns of diseases:
• Predisposing Factors
That makes the body more susceptible to disease and may alter the course of disease.
Examples include gender, genetic background, climate, age, fatigue and inadequate nutrition.
Females have higher incidence of UTI than males, males have a higher rates of pneumonia and meningitis.
Development of Diseases:
Once a m.o overcomes the defenses of the host, development of disease follows a certain sequence of steps that tends to be similar whether the disease is acute or chronic.
The stages of a disease are:
Period of incubation
Prodromal period
Period of illness
Period of Decline
Period of convalescence
Period of incubation:
The time interval between the initial infection and the 1st appearance of any signs and symptoms.
In some diseases, the incubation period is same and in others, it is quite variable.
The time of incubation depends on the specific microbes involved, its virulence, the number of infecting m.o and the resistance of host.
Prodromal period:
The Prodromal period is a relatively short period that follows the period of incubation in some diseases.
The Prodromal period is characterized by early, mild symptoms of disease, such as general aches and malaise, and certain very specific symptoms, such as Koplik’s spots in measles.
Period if Illness:
During the Period of illness, the disease is most acute.
The person exhibits over signs and symptoms of disease, such as fever, chills, muscle pain (myalgia), sensitivity to light (photophobia), sore throat (pharyngitis), lymph node enlargement (lymphadenopathy) and GIT disturbances.
The No. of WBC may increase or decrease.
Generally, the patient’s immune response & other defense mechanisms overcome the pathogens and the period of illness ends.
When the disease is not successfully overcome, the patient dies during this period.
Period of Decline:
The signs and symptoms decline.
The fever decreases, and the feeling of malaise diminishes.
During this phase, which may take less than 24 hrs to several days, the patient is vulnerable to secondary infections
Period of convalescence:
The person regains strength and the body returns to its prediseased state.
Recovery has occurred.
Reservoirs of infection:
The source of disease may be
A living organism or
An intimate object.
They provide a pathogen with adequate conditions for survival and multiplication and an opportunity for transmission. such a source is called a Reservoir of Infection.
These reservoirs may be human, animal or nonliving.
Animal Reservoirs:
Both wild and domestic animals are living reservoirs of m.o that can cause human diseases.
Diseases that occur primarily in wild and domestic animals and can be transmitted to humans are called Zoonoses.
e.g:
Some type of influenza (transmitted by wild birds)
Rabies (transmitted by wild bats, foxes, dogs and cats)
Lyme disease (transmitted by ticks)
About 150 zoonoses are known.
The transmission of zoonoses to humans can occur via one of many routes:
By direct contact with infected animals
By direct contact with domestic pet waste
By contamination with food and water
By contact with contaminated hides, fur or feathers
By consumption of infected animal products
By insect vectors
Non living Reservoirs:
The 2 nonliving reservoirs of infectious disease are soil and water.
Soil harbors such pathogens as fungi, which cause mycoses and Clostridium botulinum which causes botulism.
Water that has been contaminated by the feces of humans and other animals is a reservoir for several pathogens, most notably those responsible for GIT diseases.
Transmission of Disease:
The causative agents of disease can be transmitted from the reservoir of infection to a susceptible host by 3 principle routes:
1. Contact
2. Vehicles
3. Vectors
Contact of Transmission:
Contact Transmission is the spread of an agent of disease by
Direct contact
Indirect contact
Droplet transmission
Direct contact Transmission:
Direct contact transmission, also known as person to person transmission, refers to the direct transmission of an agent by physical contact between its source and a susceptible host, no intermediate object is involved here e.g touching.
Some examples of diseases: common cold, flu, staphylococcal infections, AIDS, STDs.
To guard against potential pathogens heath personnel uses gloves.
Some pathogens can be transmitted by direct contact from animals to humans such as rabies and anthrax.
Indirect contact Transmission:
Occurs when the agent of disease is transmitted from its reservoir to a susceptible host by means of nonliving object.
The general term for any nonliving object is Fomite.
e.g of fomites are tissues, handkerchief, towels, bedding, drinking cups, eating utensils, toys, money and thermometers.
Contaminated syringes are fomites for AIDS and hepatitis B.
Other fomite may transmit disease like tetanus.
Droplet Transmission:
Microbes are spread in droplet nuclei that travel only short distances.
These droplets are discharged into the air by coughing, sneezing, laughing or talking and travel less than 1m from the reservoir to host.
e.g of diseases are influenza, pneumonia, and whooping cough.
Vehicle Transmission:
The transmission of disease agents by a medium such as water, food and air. Other media include blood and other body fluids, drugs and IV fluids.
In Waterborne transmission, pathogens usually spread by water contaminated with untreated or poorly treated sewage. e,g. shigellosis, leptospirosis, cholera.
In Foodborne transmission, pathogens are transmitted by contaminated food. e.g food poisoning.
Airborne transmission refers to the spread of infection by droplet nuclei that travel more than 1 m from reservoir to host. e.g: measles, TB.
Vectors:
Arthropods are most important vectors.
They transmit disease by 2 general methods:
Mechanical Transmission is the passive transport of pathogens on the insect’s feet or other body parts. For e.g houseflies can transfer the pathogens of typhoid fever and shigellosis from feces of the infected people.
Biological Transmission is an active process and is more complex, mainly by bite. Some protozoan and helminthic parasites use vectors as host for a developmental stage in their life c
Ways to prevent infection:
Avoid close contact with people who are infected.
Use tissues if you have a cold or flu and throw them away.
Wash hands especially before eating, after using toilet, or after contact with someone who has an infection.
Don’t touch other people’s blood or body fluids (e.g. soiled tissues from someone who has a cold).
Don't share toothbrushes, eating utensils, etc.
Eat nutritious food to keep the body healthy.
Nosocomial Infection:
Infection acquired as a result of a hospital stay.
Also called Hospital-Acquired infections
Nosocomial infections result from the interaction of several factors:
M.o in the hospital environment
The compromised status of the host
The chain of transmission
Compromised host:
A compromised host is one whose resistance to infection is impaired by disease, therapy, or burns.
Two principal condition can compromise host:
Broken skin or mucous membranes and
A suppressed immune system
Drugs, radiation therapy, steroid therapy , diabetes, leukemia, kidney disease, stress and malnutrition can affect the actions of T and B lymphocytes and compromise the host
Introduction to Fungi
A Brief Introduction
n Mycology means the study of mushrooms (Greek, mykes = mushroom, logos = discourse).
n The systemic study of fungi began with the invention of microscope.
n The Italian botanist Pier’ Antonio Micheli is regarded as the founder of the science of mycology. In 1729, he published his researches on fungi.
What are fungi?
n It is difficult to give a precise definition of a fungus, largely because organisms which are regarded as fungi are very variable in form, behavior and life cycle.
n Ainsworth (1973) has listed their main characteristics:
1. Nutrition:
n Heterotrophic (photosynthesis lacking)
n Absorptive (ingestion rare).
2. Thallus:
n Origin from the substratum
n unicellular or filamentous (mycelial),,
n septate or nonseptate;
3.Cell wall:
n well-defined,
n typically chitinated (cellulose in oomycetes).
4.Nuclear status:
n eukaryotic, multinucleate
n the mycelium being homo- or heterokaryotic
n haploid, dikaryotic or diploid
5.Life cycle:
n simple to complex.
n Sexuality: asexual or sexual and homo- or heterothallic.
6.Sporocarps:
microscopic or macroscopic
7.Habitat:
ubiquitous as saprobes, symbionts, parastites,
or hyperparasites.
8. Distribution:
cosmopolitan.
There are an estimated 1.5 million fungalspecies of which around 70,000 have been described.
Importance of fungi
n Fungi are one of the most important groups of organisms on the planet. They are important in an enormous variety of ways.
a)Recycling:
Fungi, together with bacteria, are responsible for
most of the recycling which returns dead material
to the soil in a form in which it can be reused.
n Fungi are one of the most important groups of organisms on the planet. They are important in an enormous variety of ways.
b)Mycorrhizae and plant growth:
Fungi are vitally important for the good growth of most plants, including crops, through the development of mycorrhizael association. The growth of plants in turn affect the growth of animals and humans.
c)Food:
Fungi are also important directly as food for humans. Many mushrooms are edible and different species are cultivated for sale worldwide. Fungi are also widely used in the production of many foods and drinks. These include cheeses, beer and wine, bread, some cakes, and some soy bean products.
.
d)Medicines:
Penicillin, the most famous of all antibiotic drugs, is derived from a common fungus called Penicillium. Many other fungi also produce antibiotic substances, which are now widely used to control diseases in human and animal populations. The discovery of antibiotics revolutionized health care worldwide
e)Biocontrol:
Fungi such as the Chinese caterpillar fungus, which
parasitise insects, can be extremely useful
forcontrolling insect pests of crops. Fungi have been
used to control
devastate potato crops. Spittlebugs, leaf hoppers and
citrus rust mites are some of the other insect pests
which have been controlled using fungi.
Crop diseases:
Fungal parasites may also have enormous negative
consequences for crop production. Some fungi are
parasites of plants. Most of our common crop plants
are susceptible to fungal attack of one kind or
another. Fungal diseases can on occasion result in
the loss of entire crops if they are not treated with
antifungal agents.
h)Food Spoilage:
It has already been noted that fungi play a major role in recycling organic material. The fungi which make our bread and jam go moldy are only recycling organic matter. Fungal damage can be responsible for large losses of stored food, particularly food which contains any moisture. Dry grains can usually be stored successfully, but once damaged they are likely to become inedible. This is obviously a problem where large quantities of food are being produced seasonally and then require storage until they are needed.
Rotting of textile fibers:
Cotton in its natural state is very resistant to enzymatic degradation but there are fungi which attack and degrade them. Fungi frequently spoil clothes in humid warm weather.
Habitat of fungi
n Fungi can be found in any habitat, from sea water through to freshwater, in soil, on plants and animals, on human skin and even growing on microscopic crevices in CD-ROM disks!
Aquatic fungi:
Fungi are found in both freshwater and marine, growing both on surface and bottom of the water. The parasitic fungi greatly influence the ecology of aquatic habitats by causing sudden epidemic of phytoplanktonic fungi and other populations, like fishes.
Terrestrial fungi:
n These are conventionally classified into several ecological groups based on their habitats, e.g., soil fungi, symbionts and parasites.
n The soil-inhabiting fungi on the basis of the substrates utilized are classified into several substrate groups, e.g., sugar fungi, cellulose-decomposing fungi, lignin-decomposing fungi etc.
n Over 80% of fungi are associated with trees.
Some fungi have very specific associations and will grow only with one kind of tree, for example, Uloporus lividus, grows only under alders.
n Other fungi may be found in association with several different trees. Chanterelles, for example can be found linked with birch, pine, oak and beech trees.
n Soil type is also important. Some fungi may be associated with a particular tree, but only where it is growing on suitable soil. The most important factor is usually whether the soil is acidic or calcareous (chalky). Soil fertility also plays a part. Fields which have been heavily fertilized with artificial nitrates are less likely to be good mushroom hunting territory than those which have been organically fertilized.
Fungi in atmosphere (Air spora):
Air does not serve as a habitat. Only fragments and spores of terrestrial fungi adapted for aerial dispersal, constitute the air sporas. The composition of the air flora is governed only by physical factors of the air movement and not by any nutritional factors. Fungi in the atmosphere are mostly present in the troposphere up to a height of 10 km and are rarely found in the stratosphere.
Growth of fungi
n Temperature:
Most fungi will grow between 0° and 35 °C, but the optimum temperature range is 20° and 30 °C.
There are a number of thermophilic species that have a maximum temperature for growth at or above 50 °C and a minimum at or above 20°C.
The fungi has the ability to withstand extremely low temperature in a dormant state.
n pH:
In contrast to bacteria, fungi prefer an acid medium for growth, with a pH of 6 being near the optimum for most species investigated.
n Light:
Although light is not required for the growth of fungi, some light is essential for sporulation in many species.
Nutrition of fungi
n They are heterotrophs and depend upon other organisms for their carbon source. Heterotrophs can further be divided into the following categories:
1. Parasites: Organisms that derives their nutrition from the protoplasm of another organisms, called host.
2. Saprobes: Organisms that obtains their carbon source (food) from the by-products of organisms or dead organisms.
3. Symbiosis: It is the intimate association of two dissimilar organisms in a mutually beneficial relationship, e.g. lichens and mycorrhizae. This type of symbiosis is specifically referred to as a mutualistic symbiosis.
Obligate saprobes:
They live on dead matter and are incapable of infecting living organisms.
Facultative parasites (or facultative saprobes):
Some saprobes may become parasitic. Such organisms are said to be facultative parasites.
Obligate parasites:
The fungi that cannot live except of living protoplasm.
Obligate saprobes:
They live on dead matter and are incapable of infecting living organisms.
Obligate saprobes:
They live on dead matter and are incapable of infecting living organisms.
.
Ectomycorrhizae: grow on the surface of plant roots without penetrating the cells.
a. They are common in colder northern climates where decomposition is slow.
b. The fungus breaks down organic material and delivers nitrogen to the plant.
2. Arbuscular mycorrhizae: penetrate the cells of the plant root.
a. They are common in warmer grasslands and forests where decomposition is rapid.
b. The fungus delivers phosphorus to the plant.
Lichens are associations of a fungus with either an alga or cyanobacterium.
a. Lichens are the dominant species in tundra habitats and are important in breaking down rock to form soil.
b. Evidence suggests the fungus may sometimes be parasitic to its photosynthetic partner.
Parasitic fungi cause major damage to crops such as wheat, corn, and barley.
a. Many have evolved resistance to fungicides.
b. A new approach to blocking fungal infections in crops may be to infect the crop first with a benign strain of the pathogen, that is, a "live vaccine."
n Fungi have a common nutritional mode: Absorption: The transport of food from their substrate into their cell walls. The following events occur in this mode of nutrition:
- If the available food that the fungus is using is soluble, i.e. a simple organic compound, such as simple sugars and amino acids, the mycelium or yeast cells can transport the food directly through their cell wall.
- If the available food is insoluble, i.e. a large, complex, organic compound, such as lignin, cellulose and pectin, the food must first be digested. Digestion is carried out by the production of various enzymes that are substrate specific and will break down insoluble food material to soluble compounds that can be transported through the cell wall.
- Fungi usually store excess food in the form of glycogen or lipid.
Somatic Structures of Fungi
• Thallus:
a relatively short plant body stems, roots and roots; in fungi, the somatic fungi.
• Hypha:
*The fungal thallus typically consists of microscopic threads or filaments that branch in all directions,
*Each of these filaments is known as hypha.
*A hypha is made on a thin, transparent, tubular wall filed or lined with a layer of protoplasm varying in thickness.
Most fungal hyphae are 2-10 mm diameter.
Hyphae
• Cytoplasmic streaming of fungal hyphae is unidirectional, towards the tips, where growth takes place.
• Hyphae grow entirely at their tip. The key to the fungal growth lie to the apex. It is the site of active differentiation and nuclear divisions.
• The thin hyphal tip, 50-100 µm and is filled with protoplasm
• The portion behind this is evacuated &incapable of elongation.
• It helps in growth by synthesizing the cytoplasm which is transported to the tip.
• Each daughter branches behave like the parent hypha and
• forms secondary and tertiary branches behind their growing tips.
• Hyphae are usually of two types:
- Coenocytic hyphae and ii. septate hyphae.
i. Coenocytic hyphae:
These hyphae are non-septate or aseptate. These hyphae have nuclei scattered in the cytoplasm. .In the aseptate hyphae septa are cut off old, empty portions of hyphae in the hinder region and to delimit the sex organs.
ii. Septate hyphae:
The hyphae with more or less regularly occurring cross-walls.
Septum :
The protoplasm in the hyphae of most filamentous fungi is interrupted at regular intervals by partitions or cross-walls that divide each hypha into compartments or cells. The cross-walls are called septa.
There are two general types of septa:
1) Primary and
2) Adventitious.
• Primary septa:
* formed in association with nuclear division .
* laid down between daughter nuclei..
• Adventitious septa:
*Formed independently of nuclear division .
*Specially associated with changes in the
concentration of the protoplasm as it moves from one part
of the hypha to another.
Septa vary in their construction. Some are simple, others
are complex.
• Primary septa are of several types. For example,
Complete septa: in some septa growth continues until the septum in a solid plate.
Perforated septa: in some septa the septum remains incomplete, leaving a pore in the center that may often be plugged.
Dolipore septa: in the most complex fungi the septa have a special central apparatus in the form of a barrel-shaped inflation surrounded typically by a perforated membrane. These are called dolipore septa, found in basidiomycetes.
Cell structure
• Fungi have eukaryotic cell structure. They have double membrane-bound cell organelles like nucleus and mitochondria, tubular endoplasmic reticulum (ER), golgi bodies and the ribosomes.
• Exception from typical eukaryotic cells:
Ribosomes are free in the cytoplasm and not attached to ER.
Golgi bodies are not always present in fungi.
Lomasomes are particles or vesicles in pockets formed between the cell wall and plasma membrane. Their function is not yet known.
Dimorphism
• Though hypha is the characteristic unit of structure in fungi, there are fungi whose thallus may consist of a single cell. Some fungi show dimorphism and The mycelium
• exist in both mycelial and unicellular forms in different environments.
The mycelium
• The mass of hyphae consisting the thallus of a fungus is called mycelium (pl. mycelia). The mycelium of some fungi form thick strands.
Rhizomorphs: A thick strand of somatic hyphae in which the hyphae have lost their individuality, with the whole mass behaving as an organized unit. The structure of the growing tip of the rhizomorph resembles that of a root tip, hence the name.
• Mycelium may either be intercellular or intracellular.
Intercellular: fungi with intercellular mycelium absorb food through the host cell wall or membrane.
Intracellular: fungi with intracellular mycelium come into direct contact with host protoplasm.
Haustoria (sing. haustorium): intercellular hyphae of many fungi, especially of obligate parasites of the plants obtain nourishment through haustoria. Haustoria are specialized absorbing organ that penetrates the host cell through a minute pore punctured in the cell wall. They are formed as an outgrowth of the somatic hyphae. They may be knob-like in shape, elongated or branched.
Fungal tissue
Stroma: it is a compact, somatic structure like a mattress on which or in which fructifications are usually formed.
Sclerotium: it is a hard resting body resistant to unfavorable conditions. It may remain dormant for long periods of time and germinate on the return of favorable conditions.
Other cell wall components
• Gel-like components:
– Mannoproteins (form matrix throughout wall)
• Antigenic glycoproteins, agglutinans, adhesions—on cell wall surface
• Melanins—dark brown to black pigments (confer resistance to enzyme lysis, confer mechanical strength and protect cells from UV light, solar radiation and desiccation)
• Plasma membrane—semi-permeable.
Nuclear status
• The nuclei of fungi show important characteristics. They are extremely small-near the limit of the light microscope.
• In aseptate hyphae nuclei lie scattered throughout the cytoplasm. In the septate hyphae the cells may have one, two or more nuclei. In most fungi, the nuclei are haploid throughout the life cycle and the diploid stage is represented only by the zygote nucleus.
Reproduction
• Reproduction is the formation of new individuals having all the characteristics typical of the species.
• Two genaral types of reproduction are recognized in fungi:
A. sexual (characterized by the union of two nuclei) and
B. asexual (sometimes called somatic or vegetative, does not involve the union of nuclei, sex cells or sex organs).
Holocarpicc: fungi whose thallus is entirely converted into one or more reproductive structures,
Eucarpic: fungi that form reproductive structures on certain portions of the thallus, with the thallus itself continuing to perform its somatic functions. Most of the fungi are eucarpic.
Asexual reproduction
• Fungi exhibit the following mode of asexual reproduction-
- Fragmentation
- Budding
- Fission and
- Spores.
Asexual reproduction
- Fragmentation: A detached fragment of the hypha, in suitable conditions, break up into their component cells that behave as spores and give rise to a new individual. These spores are known as arthrospores. If the cells become enveloped in a thick wall before they separate from each other or from other hyphal cells adjoining them, they are called chlamydospores.
Budding: budding of vegetative cells is common in yeasts. A soft zone appears on the cell wall which bulges, constricts and finally pitches off to form a daughter cell. As the buds form, the nucleus of the parent cell divides and a daughter nucleus migrate into the bud. Budding may occur on spores also.
c. Fission: this is characteristic of bacteria and occurs only in some fission yeasts e.g., Schizosaccharomyces. In fission, the cells divide in transverse plane into two cells by constriction and later formation of a cell wall in-between.
Spores: These are the most common method of sexual reproduction in fungi. In contrast to the vegetative mycelium, the spore is characterized by-
Ceasation of cytoplasmic movement, small water content,
slow metabolism and lack of vacuoles.
Spores vary-
- In color: from green, yellow, orange, red, brown to black.
- In size: from minute to large
- In shape: from globose through oval, oblong, needle shaped to helical
- In number of cells: from one to many
- In the arrangement of cells and
Spores
• Spores may be produced asexually or sexually.
Asexual spore are of two types:
- Sporangiospores: they are formed within a sack-like structure called sporangium which is borne on undifferentiated or specialized hyphal structure called sporangiophore.
- Conidia: they are formed externally on hyphae, or more commonly morphologically differentiated conidiophores.
Sporangiospores
• Sporangiospores may be motile (zoospores) or non-motile (aplanospores).
Fungal zoospores have one or two flagella. There are at least two types of flagella in fungi.
- Whiplash: they are divided into two parts: lower or basal portion is much longer than the upper or terminal portion, which is usually very short and flexible.
- Tinsel: they are feathery structure consisting of a long thread with lateral hair-like projections termed mastigonemes.
Zoospores
• The flagella show characteristic insertion on the zoospores and form the basis on which four types of zoospores are differentiated in fungi:
- Uniflagellate zoospores with a posterior whiplash flagellum.
- Uniflagellate zoospores with an anterior tinsel whiplash flagellum.
- Biflagellate zoospores with one flagellum of each type attached apically or laterally.
- Biflagellate zoospores with two anterior whiplash flagella.
Conidia
• They are of two main types:
- Thallospores (arthrospores and chlamydiospores) and
- Conidiophores: they are formed as new structures on the thallus and are easily detachable.
Conidia may be uni- or multi-cellular.
Sexual reproduction
• Sex organs of fungi are called gametangia. These may form sex cells-the male and female gametes.
• The male gametangium is called antheridium and female, the oogonium.
• The motile male gamete is called antherozoid and the female gamete, the egg or oosphere.
Plasmogamy
- Planogametic copulation:
This involves the fusion of two naked, free gametes, one or both of which may be motile. The motile gametes are called planogametes.
Depending on the size and motility of the fusing gametes, there are three types of
planogametic copulation:
- Isogamy: two gametes are same shape and size
- Anisogamy: two gametes are morphologically similar, but different in size, e.g., Allomyces.
- Heterogamy: fusion between motile male gamete and non-motile female gamete, e.g., Monoblepharis.
Gametangial contact:
In this type of plasmogamy, the male gamete is usually represented by the nucleus contained inside the antheridium and the female gamete is represented by the egg contained in the oogonium. When the two gametangia come in contact, the male gamete nucleus migrates into the oogonium either through a pore dissolved at the point of contactor through a fertilization tube, especially developed for the purpose by the male gametangium. The two gametangia never fuse and retain their identity.
Gametangial copulation:
the entire content of the two gametangia fuse and become one. It occurs in two ways:
- Direct fusion of gamtangia: the two gametangia fuse and become one, e.g., Mucor.
- Migration of entire protoplast of one gametangium into the other through a pore: e.g., Rhizophidium. The entire gametangia act as gametes. The recipient gametangium is called the female, whereas the gametangium that fill its contests by the antheridium.
Spermatization:
Minute conidia, called spermatia empty their content when come in contact with female gametangia (a receptive hypha), e.g., Puccinia. The spermatia are carried to the female organ through wind, water, insects etc. the spermatia differ from conidia in being smaller, and incapable to germinate and give rise to new thallus.
5. Somatogamy:
Fusion between undifferentiated vegetative cells or spores is called somatic copulation or somatogamy.
Karyogamy
• After coming together, the two compatible nuclei may undergo fusion immediately to give rise to a diploid (2n) nucleus or may start a dikaryotic (n+n) association extending in various periods in different fungi.
Meiosis
The diploid nucleus in the zygote may undergo meiosis immediately or after an interval.
Sexual compatibility
• On the basis of sex, most fungi may be classified into three categories:
a. Hermaphroditic (monoecious): in which each thallus bears both male and female organs that may or may not be compatible.
b. Dioecious: in which some thalli bear only male and some thalli bear only female organs. Very few of these fungi have been discovered.
c. Sexually undifferentiated: in which sexually functional structures are produced that are morphologically indistinguishable as male or female.
• Fungi in the above mentioned sex categories belong to one or another of the following on the basis of compatibility:
- Homothallic fungi: those in which every thallus is sexually self-fertile and can, therefore, reproduce sexually by itself without the aid of another thallus.
- Heterothallic fungi: those in which in every thallus is sexually self-fertile, and requires the aid of another compatible thallus of a different mating type for sexual reproduction.
Life cycle of Fungi
Fungi display different types of life cycles centered around the sexual reproduction. Raper (1954) described seven basic types of life cycles in fungi. These are:
- Asexual cycle
- Haploid cycle
- Haploid cycle with restricted dikaryon
- Haploid-dikaryotic cycle
- Dikaryotic cycle
- Haploid-diploid cycle and
- Diploid cycle
- Asexual cycle: there is no alteration of haploid and diploid nuclear phases. The diploid phase (2n) is lacking.
Example: The entire group of ‘fungi imperfecti’.
- Haploid cycle: the life cycle is completely haploid (n) and the diploid phase is restricted
Example: lower fungi and Ascomycotina.
- Haploid cycle with restricted dikaryon: this is predominantly a haploid life cycle, but it differs in the separation of plasmogamy and karyogamy in space and time.
The gametic nulei pair to form dikaryons which multiply by mitotic divisions.
Example: higher Ascomycotina.
- Haploid-dikaryotic cycle: dikaryophase (n+n) is more extensive and also independent of the haploid phase.
Example: Most of the Basidiomycotina except some smuts.
- Dikaryotic cycle: the complete life cycle is passed on the dikaryotic phase
Example: Rusts and several smusts.
- Haploid-diploid cycle: both haploid and diploid phases come one after another.
Example: Blastocladiales and Endomycetales and Saccharomyces serevisieae.
- Diploid cycle: this type of life cycleis completely diploid
Example: number of yeasts, Blastodiales, Ooomycetes.
Categories
• The groupings or categories used in the classification of fungi are shown below:
Superkingdom
Kingdom
Division
Class
Order
Family
Genus
Species
Categories
• The superkingdom is the largest of the categories in which fungi are placed as a kingdom along with other four kingdoms. The kingdom is the next category and may include many divisions; each division may include many classes and so on down to the species, which is the unit of classification. Each of these categories may be divided into subgroups as subdivision, subclass, suborder if necessary.
• The names of fungi should end in-
Division-mycota
Subdivision- mycotina
Class-mycetes
Subclass-mycetidae
Order- ales
Family- aceae
Genus and species have no standard endings.
Classification
• The kingdom of fungi is divided into two divisions (G. C. Ainsworth, 1966) distinguished by the presence or absence of a plasmodium or pseudoplasmodium:
o Myxomycota: fungi with plasmodium or pseudoplasmodium
o Eumycota (true fungi): fungi without plasmodium or pseudoplasmodium. These are filamentous and most fungi belong to this group.
Plasmodium: it is a mass of naked, multinucleate protoplasm, moving by amoeboid movement. Pseudoplasmodium: it is an aggregation of septate amoeboid cells.
Pseudoplasmodium: it is an aggregation of septate amoeboid cells.
• The division Myxomycotais divided into 4 classes: Acrasiomycetes, Hydromyxomycetes, Myxomycetes, and Plasmodiophoromycetes.
• The division Eumycota is divided into 5 subdivisions:
- Mastigomycotina (4 classes): Chytridiomycetes, Hypochytridiomycetes, Plasmodiophoromycetes and Oomycetes.
- Zygomycotina (2 classes): Zygomycetes, Trichomycetes.
- Ascomycotina (6 classes): Hemeascomycetes, Loculoascomycetes, Plectomycetes, Laboulbeniomycetes, Pyrenomycetes and Discomycetes.
- Basidiomycotina (3 classes): Teliomycetes, Hymenomycetes and Gasteromycetes.
- Deuteromycotina (3 classes): Blastomycetes, Hyphomycetes and Coelomycetes.
*Class Plasmodiophoromycetes is included in both Myxomycotina and Eumycotina, because of certain common characteristics.
Class: Chytridiomycetes
Unique characteristics:
• Zoospores having a single posterior whiplash flagellum.
Variable characteristics:
• Coenocytic thallus: three forms
§ Oval multinucleate cell
§ A small elongated hypha
§ A well-developed mycelium
• Zygote is converted into a resting spore or a resting sporangium except one order (blastocladiales) where the zygote gives rise to a diploid coenocytic thallus.
The thallus
• The thallus may consist of a simple spherical structure, which may be holocarpic or eucarpic. From the vegetative part, fine thread-like structures called rhizoids arise which serve to anchor the unicellular thallus to the substratum and also absorb food. Some spores produce a network of rhizoids called rhizomycelium.
• The rhizomycelium in such fungi functions as the somatic part which bears one or more reproductive structures.
Monocentric thallus: If the thallus consists of rhizomycelium and a single reproductive structure, the thallus is called monocentric.
Polycentric thallus: When there are many reproductive structures with a rhizomycelium, the thallus is called polycentric.
The thallus may be-
• Endobiotic: growing inside the host cell,
• Epibiotic: growing attached externally, but sending rhizoids inside host cells,
• Interbiotic: attached to many hosts through the rhizomycelium.
• Polycentric thallus: When there are many reproductive structures with a rhizomycelium, the thallus is called polycentric.
Reproduction
• Both sexual and asexual reproductions are found. Asexual reproduction takes place by means of zoospores. The whole thallus, or part of it , is converted into a zoosporangium. Zoospores inside the sporangium, escape through one or more discharge papillae formed on the sporangial wall or at the tip of discharge tubes arising from sporangium.
Operculum: In some species, the discharge papillae form a distinct circular, lid-like structure called the operculum, which is pushed out, or thrown off during the release of the zoospores.
Asexual reproduction
Operculate: species forming operculum are known as operculate.
Operculation: the process by which operculum is formed. There are three methods for operculation.
1. Inoperculation: the wall of the papilla becomes thin and dissolves. A clear concave zone of non-sporangeous cytoplasm develops beneath it. Zoospores are formed in the lower sporangious zone of the cytoplasm. At the time of discharge, the concave mass of cytoplasm emerges, out and expands. The zoospores passively move into it and after a period of rest, become motile in centripetal order and burst away.
Asexual reproduction
- Exo-operculation (true operculation): the operculum is a distinct and persistent structure derived from the wall of the papilla. The operculum of this type is called exo-operculum. Beneath the exo-operculum a concave zone of non-sporangeous cytoplasm develops as in the inoperculate type. Upon dehiscence, the operculum lies hinged to the rim of the pore for some time, but later it is detached. The zoospores dart away after a short period of rest.
- Endo-operculation: the tip of the papilla inflates and dissolves forming a pore which is then plugged by a gelatinous material. Beneath the plug, the protoplasm forms a dense convex zone, which solidifies to form a operculum. The wall of the endo-operculum is continuous with the side wall of the papilla. The side wall of the papilla persists after detachment of the lid.
Sexual reproduction
Sexual reproduction may be brought about by any of the following methods:
Planogametic copulation
Gametangial copulation
somatogamy
Economic importance
• The Chytridiomycetes include many important obligate parasites in the order Chytridiales, e.g., Synchytrium, Physoderma and Urophlyctis, which cause serious plant diseases. Aquatic chytrids (a common name for fungi belonging to order Chytridiales) cause frequent epidemics of algae (both fresh water and marine) and by this disturb the habitat and food chain.
• Members of some families in the order Blastocladiales include many endoparasites of arthropods.
• The genera Blastocladiella and Allomyces have been used extensively in morphogenic studies.
Order: Chytridiales
• The fungi included in this order are usually referred to as chytrids. They live as parasites or saprophytes in water and soil.
Family: Olpidiaceae
Thallus: endobiotic and holocarpic
Sporangium: inoperculate
Sexual reproduction: planogametic copulation (isogamy)
Zygote: biflagellate diploid, penetrates the host.
Genus: Olpidium
• About 30 species of Olpidium are knownwhich occur in water or wet soils as parasites of algae and roots of some higher plants. An important root parasites of vascular plants is O. brassicae, causing damping off of crucifer seedlings and other unrelated hosts.
• O. brassicae serves as a vector of at least three viruses in soil, such as, lettuce ‘big vein’ virus (BVV), tobacco necrosis virus (TNV) and tobacco stunt virus (TSV). The viruses are disseminated by zoospores and also survive in the resting spores for several months. Whether the viruses multiply also in the zoospores is not yet known.
Life cycle of Olpidium brassicae
• The posteriorly uniflagellate zoospores swim actively in the water. When they come in contact with the roots of the host plant, they settle down on the root hairs, loss the flagellum and encyst (develop a wall). A pore is dissolved on the root hair, the protoplast enters the root cell while the cyst is left emptied. Inside the host cell, by growth and nuclear divisions it develops into a multinucleate single-celled thallus. In 4 to 5 days, the whole thallus is transformed into a zoosporangium. The contents cleave into zoospores. Exit tube originate from the thallus which penetrates the host cell wall and open outside. The tip dissolves, the zoospores rush out and reinfect the hair roots.
Life cycle of Olpidium brassicae
• The sexual phase is initiated when two zoospores, behaving as planogametes, fuse. The planogametes most frequently originate from different sporangia, but sister planogametes have also been observed to fuse. Copulation of two gametes result in the formation of a motile zygote, but karyogamy is postponed for some time. The zygote infects a host cell in the same manner as does a zoospore, but develops into a thick-walled resting sporangium that does not immediately discharge zoospores and is capable of overwintering.
Life cycle of Olpidium brassicae
• The sporangium is binucleate at first, but before germination, karyogamy takes place, probably followed by meiosis. Several nuclear divisions result in a multinucleate structure, the protoplast of which eventually undergoes cleavage into presumably uninucleate zoospores. These escape and may reinfect host cell.
Family: Synchytriaceae
• Thallus: endobiotic and holocarpic
• Nutrition: Parasitic
• Sporangium: inoperculate
• Sexual reproduction: planogametic copulation (isogamy)
• Zygote: biflagellate diploid, penetrates the host.
* Thallus is divided into several sporangia (or gametangia), which are covered by a common membrane and it is then called a sorus.
In some species, e.g., Synchytrium endobioticum, the thallus may pass its content into a vesicle which later forms the sorus. Thus the thallus behaves as a prosorus. In still other cases, e thallus instead of transforming into a sorus or prosorus, may form a thick-walled resting spore.
Synchytrium endobioticum
It causes the black wart disease of potato. This fungus serves as a vector of potato virus X (PVX).
Black wart disease is characterized by the dark brown or black cauliflower-like outgrowths appear on the tuber. The disease is best-controlled by using immune and resistant verities of potato for cultivation.
Life cycle of Synchytrium endobioticum
• In soil the resting spores germinate and give rise to haploid zoospores in the presence of the potato seedlings. The germination of resting spores requires moisture and low temperature.
• Wall-less and posteriorly uniflagellate zoospores infect the tubers through the eyes (bud) or the epidermis of the young tubers. The zoospores then shed the flagellum and enter into the host cell through a pore, dissolved by their enzyme activity.
• In the host cell the naked, unicellular thallus grows with nutrition from the host. The cells around the infected cell are stimulated to uncontrolled growth , which ultimately gives rise to warty outgrowth.
• At this stage the thallus is termed a prosorus. The prosorus settles at the bottom of the infected cell, which is dead by this time. The prosorus now germinates. A pore is formed on its outer wall through which the inner hyaline wall protruded out to form a vesicle into which the uninucleate cytoplasm migrates. The vesicle then develops into the sorus containing several sporangia surrounded by a common membrane. The nucleus forms about 32 nuclei by repeated mitotic division. The cytoplasm cleaves into 4-9 multinucleate segments by thin hyaline walls. These are called sporangia.
• Each sporangium, by further nuclear divisions, come to have about 200-300 nuclei. Finally each nucleus with some surrounding cytoplasm is differentiated into a zoospore. Under favorable conditions, the zoospores are liberated from the sporangia into the soil. The zoospores can reinfect the potato tubers. This continues throughout the crop season and several successive generations of zoospores are produced which cause repeated infections resulting in severe infection.
• With the arrival of dry season, the zoospors behave as gametes and undergo fusion to bring about sexual reproduction. The gametes are smaller in size than zoospores. All gametes are similar in size (isogametes). Only gametes produced in different sporangia fuse to form a bigger biflagellate zygote cell.
• The biflagellate zygote cell infects the tubers like the zoospores. Karyogamy occurs before penetration and therefore, the fungal thallus that grows in the epidermis is diploid.
• The diploid fungal cell lies at the bottom of the infected host cell and develops a thick, two-layered wall and transforms into a resting spore (resting sporangium).
• The resting spores are released into the soil due to the decay of the tubers. The resting spores germinate after about 2 months of dormancy when the host is available, otherwise they are capable of long survival.
• Whether the motile cells will be asexual zoospores or sex cells (gametes) seems to depend on the presence or absence of sufficient water.
Ascomycetes
Important features
1 .chitinous cell walls
2. hyphae with regular cross-walls called septa
3. the ability of somatic, assimilative hyphae to fuse with one another and to exchange nuclei
4. the occurrence in their life cycles of a unique nuclear phenomenon called the dikaryon.
5 ) members are commonly known as the Sac Fungi. Characteristically, when reproducing sexually, they produce nonmotile spores in a distinctive type of microscopic cell called an "ascus"
6) spores are called ascospores
Asexual reproduction
1) Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid expansion of these fungi into areas which were previously not colonized. It occurs through reproductive structures, the "conidia," which are genetically identical to the parent and mostly have just one nucleus. They are also called "mitospores" due to the way they are generated through the cellular process of mitosis. They are generally formed on the ends of specialized hyphae, the "conidiophores". Depending on the species they may be dispersed by wind or water, or also by animals.
2)Asexual spores
It is important to consider the spores, which can be distinguished by colour, form and the way they are separated into cells.
Sexual reproduction
Sexual reproduction in the Ascomycota is marked by a characteristic structure, the ascus, which distinguishes these fungi from all others. An ascus is a tube-shaped vessel, a meiosporangium, which contains the sexual spores produced by meiosis. The latter are called ascospores in contrast to the asexual conidiospores.
Saccharomyces
.Buds are observed. They are unicellular, globose, and ellipsoid to elongate in shape.
. Hyphae are absent.
Saccharomyces produces ascospores
• These ascospores are globose and located in asci. Each ascus contains 1-4 ascospores.
• Asci do not rupture at maturity
Two haploid cells that differ in mating type, called a and £\, can mate to form a diploid a/£\ cell, which multiplies by budding. Under starvation conditions, diploid cells undergo meiosis, forming haploid ascospores. Rupture of an ascus releases four haploid spores, which can germinate into haploid cells. Once each generation a haploid cell is converted to the opposite mating type
Aspergillus
Aspergillus is a genus of around 200 molds found throughout much of nature worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli.
Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds on the surface of a substrate, as a result of the high oxygen tension
Aspergillus species are common contaminants of starchy foods (such as bread and potatoes), and grow in or on many plants and trees.
Asexual reproduction
Development of Phillades
At the time of philade formation ,many thin area appears in the thick vesicle wall owing to to the dissolution of wall material.The vesicle cytoplasm near this thin areas is pushed out synchronousley in the form of oval or bottle shaped outgrowths
.This outgrowth represent the phillades or sterigmata
1)Asexual RP is also take place by conidia or condiophore .
2)At the time of asexual rp many erect hyphae are seen developing from the somatic hyphae .This long ,aseptate and unbranched hyphae are called conidiophores.The hyphal cell that give rise to conidiophore is called the foot cell .
3)Conidiophore terminate into globular or bulbous head are called vesicle .The vesicle is multinucleate and from its entire surface it developes sterigmata .
4)At the tip of sterigmata or philadae s it developes many small, globose unicellular or uninucleate or multinucleate bodies called conidia .
5)Conidia later dispersed by air and germinate by producing germ tubes
Penicillium
- Mycelium is well branched and consist of many septate hyphae ,which are branched ,tubular and generally hyaline .
2.The septa have central pore which allows the cytoplasm and nuclei to flow from cell to cell .
3.Some of the hyphae enter into the substratum to absorb the food material ,wheres others remain on surface to produce conidiophores and conidia .
Asexual Reproduction
1)Asexual RP is also take place by conidia or condiophore .
2)A conidiophore is an erect ,tubular hyphal outgrowth which may develeop from the any cell of the mycelium ,but not from specialized foot cell as mycelium .
3)Conidiophore terminate into unbranched phialides or sterigmata .
4)Then conidia develop from this sterigmata .
5)A conidiophores with philades and terminal chains of conidia appears like of an artist brush and hence it is called penicillus .
Economic importance ---Negative effect
Ascomycetes make many contributions to the good of humanity, and also have many ill effects.
Dutch Elm Disease, caused by the closely related species Ophiostoma ulmi and Ophiostoma novo-ulmi, has led to the death of many elms in
Members of the Ascomycota such as Stachybotrys chartarum are responsible for fading of woollen textiles, which is a great problem especially in the tropics
Blue-green, red and brown moulds attack and spoil foodstuffs -
Aspergillus flavus, which grows on peanuts and other hosts, generates aflatoxin, which damages the liver and is highly carcinogenic
Positive effect
The most famous case may be that of the mould Penicillium chrysogenum (formerly
Penicillium notatum), which, probably to attack competing bacteria, produces an antibiotic which, under the name of Penicillin
Some ascomycete fungi can be altered relatively easily through genetic engineering procedures. They can then produce useful proteins such as insulin, human growth hormone,
Baker's Yeast (Saccharomyces cerevisiae) is used to make bread, beer and wine, during which process sugars such as glucose or sucrose are fermented to make alcohol and carbon dioxide.