2 Fungi Definition Includes Kingdom Fungi Kingdom Protista Species Eucaryotic, spore-gearing organisms with absorptive nutrition, no chlorophyll, and that reproduce sexually and asexually.IncludesKingdom FungiLower fungiHigher fungiKingdom ProtistaSlime molds (cellular and acellular)Species90,000 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.AerobesUsually aerobic;Some facultative anaerobes e.g. yeasts in alcoholic fermentation.Obligate anaerobes found in ruminants.Most are saprophytesExtracellular hydrolytic enzymes; hydrolysis; absorption of hydrolyzed products.
4 Importance in the biosphere SaprophytismPrimary colonizers of plant litter Most fungal species can feed on complex polymersPolymers 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 SymbiosisMycorrhiza (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 pathogensLichens (alga/fungus) Sugars; fats; peptides by lower fungi and slime molds.
6 Importance in the biosphere Parasitism and predationPlants 8,000 spp. of fungi cause disease e.g. rusts and take all in wheat; potato blightAnimals 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 MycotoxinsSecondary metabolites highly toxic to animals (ppm concentrations)ExamplesAflatoxin 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 usesChemicals 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 BiodegradationDamage by saprophytes results in economic losses.Fungi are ubiquitous.Nutrients for saprophytic growth found in:FoodstuffsBuilding materialsTextilesPackagingControl 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 BioremediationReduction of waste materials by exploiting the biochemical capability of the fungi e.g.Cellulosic materials e.g. compostingEffluent treatment e.g. biobleaching
11 Structure Filamentous Dimorphism Septa Hyphae Mycelium (pl. mycelia) Pseudomycelium (single-cells; no cytoplasmic streaming)DimorphismYeast form ↔ Mycelial formYM shiftSeptaNon-septate (coenocytic)Septate (acoenocytic)Uni- or multiperforate septa permits cytoplasmic streaming
12 Growth Filamentous fungi grow by hyphal extension Propagule Hyphal tips; hyphal fragments; sporesHypha/hyphae Daughter cells by central constriction and formation of septaMycelium (pl. mycelia)Colony (thallus)Yeasts grow by budding
13 Growth Growth measured in Colony massColony diameterTo produce growth curves similar to that of the bacteriaMetabolic products typically occur at different stages of the growth curvePrimary metaboliteSecondary metaboliteBiomassMetabolite
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.