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Summer Bio153S: lecture 9 biology of fungi (I) • fungi used to be considered primitive plants • now thought to be phylogenetically closer to animals • monophyletic group > 600 my old • ~ 100,000 described spp. • may be 1.5 million spp. fungi are heterotrophs • “osmotrophs”: digest, then ingest • hydrolytic exoenzymes • can break down lignin, cellulose (also petroleum, waxes, photographic film…) • saprobes, parasites, predators, mutualistic symbionts… • some exist as single cells (yeasts) • most multicellular • body = mass of hyphae • cell walls contain chitin (N–rich polysaccharide) mycelia can be huge!! • a honey fungus in Oregon: • 860 ha • 2,600 years old! Armillaria ostoyae • 1 cm3 of soil : 1 km of hyphae; surface area > 300 cm2 • mycelia are nonmotile; grow rapidly • ↑ hyphal length rather girth; maximize SA : Vol 1 structure of hyphae: modified hyphae: • haustorium: modified hypha for penetration predaceous fungi: origins: • evolved from unicellular, aquatic, flagellated ancestor • member of clade Opisthokonta (includes animals & some protists) • adaptive radiation: colonized land ~ 460 m.y. old fossil • flagella may have been lost more than once paraphyletic? 2 Chytridiomycota: • ancestral form • mostly freshwater; some are commensals in guts of mammals (anaerobic) • saprobes and parasites Zygomycota: • 1,000 species • molds etc. • some single cells • unique: motile spores (zoospores) other Zygomycota: • Microsporidia: unicellular parasites • affect people with HIV recently classified in Zygomycota Rhizopus (bread mold) Glomeromycetes: • formerly in Zygomycota • all form mycorrhizae (symbiotic associations with roots of plants • 90% of plant species Ascomycota • some secondarily unicellular (derived) e.g. Saccharomyces • reproductive structure = ascus Geopora cup fungus 3 Ascomycota powdery mildew black spot ~40% of Ascomycota: symbiosis with algae, cyanobacteria - LICHENS • diverse, probably evolved from parasitism • extremely resistant, except to SO2 • prominent in Arctic; soil formation Basidiomycota • most “mushrooms” and bracket fungi • important decomposers • some pathogens (rusts & smuts) lichens: Geastrum Lycoperdon Basidiomycota Basidiomycota Auricularia Phlogiotis Amanita Phallus Tremella Ganoderma 4 Saprobes • dead organic material - scavengers • decomposers, cycling C, N etc. (as do bacteria) • “fairy ring”: outward growth of mycelium; appearance of fruiting bodies Saprobes in direct competition with bacteria; some bacteria prey on fungi fungi respond: secreted metabolites ⇒ kill or inhibit bacterial growth • antibiotics & bacteriostats • suppress immune system e.g. cyclosporin Parasites • parasite affects host behaviour and physiology • direct impact of secreted chemicals on nervous system • ergot of rye; Salem witches • abundant in soils • intimate association with roots Parasites • virtually all animals & plants are susceptible • plant pathogens; blights, mildews, rusts • plants can evolve resistance; fungi respond by castrating hosts FungusFungus-garden ants: • ants feed and tend fungus in special chambers • fungal hyphae are sole food of larvae 5 FUNGI & HUMANS HARM rot, decay of foods and goods; direct poisons disease of humans; domestic organisms HELP edible fungi; cheese manufacture Saccharomyces cerevisiae yeast -> bread, wine, beer, whiskey Aspergillus - soy sauce 6