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Berkeley BIOLOGY 1B - Fungi Lectures

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1Fungi LecturesBio 1B, Fall 2008Instructor: Thomas Carlson2Fungi• Fungi are more closely related to animals than plants• Fungi and Animals:– Chitin in cell walls of fungi and in exoskeletons of invertebrates– Flagella– Store carbon by synthesizing glycogen polysaccharide• Plants:– Cellulose in cell walls– Store carbon by synthesizing starch polysaccharide3Nutrition & Habit:• Land Plants: photosynthesis• Fungi: absorb nutrients from living or deadorganisms• Animals: absorb nutrients from living ordead organisms• Land Plants: do not live on or in humans• Fungi: may live on and/in humans4Fungi have an absorptivelifestyle:Some are parasitic or mutualistic• absorb nutrients from living plants, animals, humansSome are saprophytic• absorb nutrients from dead/decomposing plant and/oranimal tissue• recycle nutrients back into the biosphere5Fungi grow in two ways:• multicellular mycelia e.g., mushrooms• single-celled yeasts• baker’s yeast, Saccharomyces cerevisiae (Fig 31.7)• Candida albicans (a commensal fungus living inand on humans that can be pathogenic in humans)6Multicellular mycelium(Figs 31.2, 31.3, 31.4)• composed of filaments known as hyphae• Mushrooms consist of densely packed hyphae• Hyphae (Figs 31.2, 31.3, 31.4)– long narrow tubular filaments optimizes surfacearea/volume ratio which enhances absorption– hyphae may be broken into compartments by septa thatcontain gaps which enables movement of materialsbetween compartments789Saprophytic fungi:• Saprophytic fungi are decomposers thatreverse biosynthesis by breaking down plantand animal tissue and recycling nutrientsback into the biosphere• Some fungal organisms can digest wood10Extracellular digestion bysaprophytic fungi:Fungi secrete digestive enzymes outsideof their hyphae:! breakdown cellulose, starch, lignin,proteins, & RNA into! smaller compounds e.g., sugars, aminoacids, nucleic acids! able to diffuse across the cell membraneinto the hyphae11Lignin and cellulose degrading fungi playimportant role in global carbon cycle• Lignin degradation:– hyphae excrete lignin peroxidase into extracellularenvironment! breaks down dense lignin matrix around long strandsof cellulose• Cellulose digestion:– Cellulases excreted into extracellular environmentbreakdown cellulose12Concentration of fungal spores are attimes comparable to pollen grains in air samples• Spores fall on food source! germinate! mycelium forms! grows in direction of food! when food source diminishes, spores are produced• With adequate food sources mycelia can be largeand long-lived13In Northwest USAa massive individual mycelium–1290 acres (6.5 square km)–hundreds of tons–thousands of years old–one of the largest most long lived organisms known14MutualismsBoth fungus and host plant derive benefit• Mycorrhizae (31.4b, 36.5, 37.12)• common association between fungi & land plant roots• fungi make nitrogen and phosphorous available to plants• fungi receive sugars & other carbon sources from plant1516Ectomycorrhizal Fungi (EMF)(Fig 37.12a)• Dense network of hyphae around roots• Found in almost all tree species intemperate & boreal forests• Basidiomycetes often form this type ofassociation17Ectomycorrhizal Fungi (EMF)• Short growing season in temperate areas! slow decomposition! nitrogen remains tied up in dead tissues• EMF releases peptidases that cleave peptidebonds of amino acids! nitrogen is released & absorbed by the fungal hypha! transported close to tree roots ! absorbed by plant18Arbuscular mycorrhizal Fungi(AMF) = Endomycorrhizae(Fig 31.15, 37.12b)• Grow in cells of root tissue• Found in 80% of all plant species• Glomeromycetes fungi• Supply plants with phosphorous• Especially in grasslands & forest in warm &tropical habitats where the growing season islong and nitrogen is available19Lichens (Fig 31.23 & 31.24)• Results from the symbiotic association of a truefungus and either a cyanobacteria or a green alga• Most fungi are ascomycetes & some arebasidiomyctes• Live in tundras and on bare rock! contribute to rock breakdown and soil formation• Fungi provides protection to cyanobacteria orgreen algae• Algae or cyanobacteria provide carbohydrate tofungus2021Parasitism• On Plants: (Fig 31.25)– Parasitic fungi killed billions American chestnut &American elm trees (Dutch elm disease)– Corn smut fungal infection– Tar spot on maple leaves– Ergot infection (Claviceps pupurea) in rye grains• On Animals:– Chytridiomycota species infect & kill frogs– Cordyceps fungi infects certain caterpillars• On Humans:– Coccidiodomycosis (Valley Fever) causes fungalinfection in humans living in the central valley ofCalifornia. Humans get infected by inhaling fungalspores into their lungs.22Ascomycete Cordyceps fungus growing out of headof caterpillar2324Evolution of Fungi (Figs 31.11)• Chytridiomycota and Zygomycetes– branched off very close together in time and are theearliest known fungal groups• Glomeromycetes– form endomycorrhizae called arbuscular mycorrhizae• Basidiomycota and Ascomycota– represent later, more derived groups252627Chytridiomycota (Fig 31.11, 31.12)• only fungi group that are aquatic• infections in frogs e.g., Batarachochytriumdendrobatidis epidemic infection in mountainyellow-legged frogs in Sierra Nevada mountainsof Califonia• motile cells– gametes in sexual reproduction– spores in asexual reproduction• centrioles associated with nuclear membraneduring cell division28Zygomycota (Fig 31.13)• Most live in soil• zygote with tough outer coat• Some have mutualistic arbuscular mycorrhizalrelationships• Some live on bread e.g., Rhizopus stolonifer• Hyphae are haploid29Zygomycota Reproduction (Fig 31.13)• Two different mating types become yoked together! haploid nuclei fuse! diploid zygote is resistant to extreme conditions! favorable conditions enable meiosis! meiotic products produce haploid cells! spores are released, germinate, and grow into newmycelia30Glomerulomycota (Fig 31.11)– All form distinct types of endomycorrhizae calledabruscular mycorrhizae– Tips of hyphae push into plant root cells andbranch into treelike structures called arbuscules31Ascomycota (sac fungi)(Fig 31.16, 31.17)• Some are microscopic yeast (e.g., Candidaalbicans)• Some have sac-like spore producingstructures and multicellular mycelia32Fungi in Ascomycota group(Fig 31.16, 31.11)• Lichen fungi (e.g., Cladonia &


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Berkeley BIOLOGY 1B - Fungi Lectures

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