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Fungi 1 Importance; Structure & Growth

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Presentation on theme: "Fungi 1 Importance; Structure & Growth"— Presentation transcript:

1 Fungi 1 Importance; Structure & Growth

2 Fungi Definition Includes Kingdom Fungi Kingdom Protista Species
Eucaryotic, spore-gearing organisms with absorptive nutrition, no chlorophyll, and that reproduce sexually and asexually. Includes Kingdom Fungi Lower fungi Higher fungi Kingdom Protista Slime molds (cellular and acellular) Species 90,000 sp. described; 1.5 million spp. estimated to exist (Prescott et al., 1999).

3 Fungi Chemoorganotrophs Aerobes Most are saprophytes
Organic compounds as sources of carbon, electrons and energy. Most use carbohydrates and nitrogenous compounds to synthesize their own amino acids and proteins. Aerobes Usually aerobic; Some facultative anaerobes e.g. yeasts in alcoholic fermentation. Obligate anaerobes found in ruminants. Most are saprophytes Extracellular hydrolytic enzymes; hydrolysis; absorption of hydrolyzed products.

4 Importance in the biosphere
Saprophytism Primary colonizers of plant litter Most fungal species can feed on complex polymers Polymers Long chain, branched and aromatic organic molecules such as cellulose, pectin, lignin by basidiomycetes and ascomycetes. Small organic molecules Sugars; fats; peptides by lower fungi and slime molds.

5 Importance in the biosphere
Symbiosis Mycorrhiza (fungus/root) e.g. wheat/Glomus sp.; pine/Leucopaxillus sp. May/may not be obligate May (endo-)/may not (ecto-) enter the host Fungus receives plant photosynthate Plant receives mineral nutrients and protection from pathogens Lichens (alga/fungus) Sugars; fats; peptides by lower fungi and slime molds.

6 Importance in the biosphere
Parasitism and predation Plants  8,000 spp. of fungi cause disease e.g. rusts and take all in wheat; potato blight Animals  50 spp. of mostly opportunistic yeasts. Systemic mycoses of internal organs e.g. Candida albicans candiasis of the intestinal thrush. Superficial mycoses e.g. Trichophyton spp. which cause ringworm and athelete’s foot. Nematode-trapping fungi.

7 Importance in the biosphere
Mycotoxins Secondary metabolites highly toxic to animals (ppm concentrations) Examples Aflatoxin from Aspergillus flavus A. flavus grows in maize and cereals under warm, moist storage; and in peanut pods underground before harvest. Causes aflatoxicosis. Amanitin from Amanita muscaria Toadstools (hallucinations; liver damage; death). Ergot alkaloids from Claviceps purpurea Ergotism from ingestion of infected seedheads of rye and grasses.

8 Importance in the biosphere
Industrial, food and agricultural uses Chemicals e.g. antibiotics; organic acids. Biomass e.g. mushroom; mycoprotein. Food fermentations e.g. tempe; cheese; alcohol production; bread; soy sauce. Biocontrol agents e.g. mycoherbicides; mycoinsecticides. Also see lectures on Agricultural Microbiology and Industrial Microbiology

9 Importance in the biosphere
Biodegradation Damage by saprophytes results in economic losses. Fungi are ubiquitous. Nutrients for saprophytic growth found in: Foodstuffs Building materials Textiles Packaging Control measures based on imposition of unfavorable environment on the fungus e.g. gas/vacuum packaging; chemical inhibitors; asepsis; water activity; temperature control.

10 Importance in the biosphere
Bioremediation Reduction of waste materials by exploiting the biochemical capability of the fungi e.g. Cellulosic materials e.g. composting Effluent treatment e.g. biobleaching

11 Structure Filamentous Dimorphism Septa Hyphae Mycelium (pl. mycelia)
Pseudomycelium (single-cells; no cytoplasmic streaming) Dimorphism Yeast form ↔ Mycelial form YM shift Septa Non-septate (coenocytic) Septate (acoenocytic) Uni- or multiperforate septa permits cytoplasmic streaming

12 Growth Filamentous fungi grow by hyphal extension
Propagule Hyphal tips; hyphal fragments; spores Hypha/hyphae Daughter cells by central constriction and formation of septa Mycelium (pl. mycelia) Colony (thallus) Yeasts grow by budding

13 Growth Growth measured in
Colony mass Colony diameter To produce growth curves similar to that of the bacteria Metabolic products typically occur at different stages of the growth curve Primary metabolite Secondary metabolite Biomass Metabolite

14 Growth Fungi can propagate via
Hyphal fragmentaion Lysis of aged parts of hyphae; other living sections to grow into new colonies. Mechanical breakage e.g. soil disturbance; break-up of substratum. Sclerotia Specialized hyphal propagules. Storage and survival structure; resistant to extreme environmental conditions. Germinate to form new hyphae or sexual spores. Rhizomorphs Hyphal aggregations growing in parallel into rope-like structures a few cm long and 1 – 2 mm thick. Transports fungus to another part of the substratum e.g. rotting wood, from where hyphae disperse and spread out.

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