FUNGI

Habitat They are found in almost every habitat where organic material is variable. Since they donot require light for photosynthesis they grow in light and dark. They flourish well in moist, dark and warm conditions but their presence at or below freezing temperature as well as in hot deserts has also been reported. The most usual habitat of fungi is wet soil rich in humus.

Habitat A few forms are aquatic (Saprolegnia) and some are subterranean .In rainy season they are seen growing on moist shoes, leather goods, wooden logs , clothes and food stuff (such as bread, jam, jellies, pickles, fruits and vegetables). Some contaminate drinking water. Some parasitic fungi grow on plants and animals including man and cause serious disease. Coprophilus fungi grow on dung and symbiotic fungi grow in association with other organisms.

Except for yeast, because it is unicellular, the body of fungus is made up of a number of elongated , tubular filaments known as hyphae. The body of a fungus having filamentous branches or network of hyphae is known as mycelium. Some hyphae are continuous tubes filled with multinucleated cytoplasm –these are called coenocytic hyphae. Others have septae or cross walls in their hyphae. The cell walls of fungi are composed of chitin and polysaccharides.

Classification Kingdom fungi is classified on the basis of morphology of the mycelium, mode of spore formation and fruiting bodies into the following classes- Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes

Reproduction in fungi it takes place by vegetative means-fragmentation, budding and fission. In fragmentation, the mycelium breaks up into two or more segments due to mechanical injury, decay, etc. Each fragment grows to form the complete mycelium. In budding (e.g. yeast) the parent cell shows protrusion at one end. The protrusion grows into a bud which ultimately separates as a new individual. In fission, the unicellular fungus like yeast divides into two daughters through division or fission of the cell

Asexual reproduction occurs through conidia or sporangiospores or zoospores. These are single –celled specialised structures which separate from the organism, get dispersed and germinate to produce new mycelium after falling on suitable substrate.

Sexual reproduction occurs through oospores, ascospores and basidiopores. The various spores are produced in distinct structures called fruiting bodies. The fruiting bodies are ascocarps and basidiocarps which contain asci and basidia respectively. The ascospores are a type of non-motile spores which are produced inside special sacs called asci. Basidiospores are non-motile which are formed exogenously (i.e.outside the body) on short outgrowths of club-shaped structure called basidium.

Sexual cycle involves three steps 1.Plasmogamy-There is union of protoplasm between two haploid hyphae of compatible mating type or gametes. 2.Karyogamy-Fusion of two nuclei is called karyogamy. In some fungi, the fusion of two haploid cell immediately results in diploid cells(2n).However in some fungi (e.g.Agaricus, Aspergillus), an intervening dikaryotic stage(n+n i.e. two nuclei per cell) occurs, such a condition is called dikaryon and the phase is dikaryophase. Later the parental nuclei fuse and the cells become diploid in karyogamy. 3.Meiosis-The fungi form fruiting bodies in which reduction division (meiosis) occurs leading to the formation of haploid spores.

Beneficial roles of fungi 1.Fungi as food- The fruiting bodies of several mushrooms and morels (e.g. Agaricus bisporus,etc) are used as food. Mushrooms are preferred for food because of their fairly high protein content and are also rich in vitamins, carbohydrates, minerals and amino acids. Yeast is an important source of vitamin B and D.

Beneficial roles of fungi 2.Fungi as medicine- Steroids are complex organic compounds , effective against rheumatoid arthritis, allergic, skin related and other diseases. A wide variety of fungi have the capacity of synthesising many steroids, for instance cortisone is prepared by fermentation of plant glycosides by Rhizopus nigricans and Aspergillus niger.

Steroids from fungi

Several yeasts like Saccharomyces cerevisiae are good sources of vitamin B-complex .

Many antibiotics are extracted from fungi Many antibiotics are extracted from fungi. Penicillin was isolated for the first time by Alexander Fleming in 1929 from Penicillium notatum.

Beneficial roles of fungi- 3.Fungi in the production of organic acids- Biochemical activities of several fungi are utilised in the commercial production of organic acids. Citric acid is produced by the fermentation of sucrose and molasses by Aspergillus niger,etc. It is used in soft drinks and other foods and medicinal preparations.

4.Fungi in industry- In brewery-Alcoholic fermentation with the help of fungi is the basis of brewing industry. Wine is produced by fermenting rice with Aspergillus oryzae.

Beneficial roles of fungi 5.Fungi in enzyme production-Fungi produce many a number of intra- and extracellular enzymes, some of which are used on a commercial scale. For example, the yeast Saccharomyces cerevisiae is used for the extraction of the enzyme invertase which is used in confectionery and paper industry.

Beneficial roles of fungi 6.Fungi in agriculture- They play important roles in agriculture in various ways. a)As agents of decomposition- The ratio of carbon dioxide in the atmosphere is maintained by the decomposition of plants and animal debris by fungi and bacteria. b) In biological control-Fungi play an important role in the biological control of diseases.

Harmful roles of fungi- 1.Fungi as pathogen- Most of the parasitic fungi are pathogenic and cause diseases in plants, especially flowering plants. The common fungal diseases of plants are smuts, rusts, mildews, blights, rots and wilts.

Harmful roles of fungi- 2.Deterioration of articles- Many important paper documents, valuable leather articles, textiles, plastic, photographic films, electronic goods, etc are deteriorated by fungi.

Harmful roles of fungi 3.Mycotoxins- Some fungi produce mycotoxins which are responsible for food poisoning ,etc.

Harmful roles of fungi- 4.Fungi are abundant in the environment and some infect humans, causing disease. Surface infections such as athlete's foot and fungal nail are common. Fungi can also cause internal diseases called invasive fungal infections. People with a weakened immune system are particularly susceptible to invasive fungal diseases.