The Fungi

fungi

eukaryotic, chemoorganoheterotophic organisms which absorb extra organismal digested nutrients

fungi nutrition

secrete digestive enzymes onto organic matter and absorb digested products (examples: are amino acids and monosaccharides)

saprophytes

absorb digested nutrients from dead organic material or wastes

symbionts

absorb digested nutrients from living organisms they live in or on

• mutalism, commensalism and parasitism

fungi composition

• lack chlorophyll; non photosynthetic

• form spores- spores are dormant, resistant structure which allows dissemination of the organism (can be blown hundreds of miles before germination)

• all can reproduce asexually and most sexually

• make up approximately 1/3 of the worlds biomass

• account for about 50% of all decomposition or organic matter into inorganic forms

  • play role in cycling of many elements

lichens

associations with algae or cyanobacteria

mycorrhizae

associations with plants roots

fermentation

yeast used in making bread, wine, beer, cheese and soy sauce

organic acids

produce citric and gallic acid

certain drugs

produce ergometrine and cortisone

antibiotics

produce penicillin, griseofulvin

immunosuppressive agents

produce cyclosporin

fungi morphology

• have cell walls and most are non-motile

• yeast are unicellular types of this

• filamentous are multicellular

• normally haploid

• mostly multicellular

yeast

any unicellular fungus, cell wall is composed mainly of mannan and have an oval or spherical shape

filamentous fungi

multicellular with cell walls composed mainly of chitin

hyphae

filamentous fungal cells and have two types

• non septate

• septate

non septate hyphae

coenocytic, multinucleate and contain no septa

septate

nuclei operated by porous partitions (not walls), smaller molecules can pass through partitions from cell to cell

thallus

body/vegeative structure of a fungus

molds

multicellular fungi are called this

mycelium

consists of long, branched hyphae filaments tangled into a mass

yeast reproduction

mostly budding and a few of these of binary fission

filamentous fungi reproduction

• fragmentation

• asexual spore formation

fragmentation

breaking in two or more pieces

asexual spore formation

• sporangia or at tips of special hyphae

• 1N spore mother cells undergo mitotic cell division to produce two genetically identical 1N asexual spores

fungi sexual reproduction

• exist in two mating types (±) and they are identical morphologically but different genetically and biochemically

• mostly there are no gametes but special 1N hyphae grow towards each other and the tips (gametangia) fuse to produce an N+N or 2N zygote

• N+N cells have genetical material and nuclei of both mating types, but the nuclei do not fuse (dikaryotuc stage in life cycle)

• This N+N zygote then undergoes mitotic cell division to form a larger, N+N structure called a fruiting body of variable morphology depending on the fungus

sexual spores are formed by

• some N+N cells develop into 2N spore mother cells by having the two nuclei fuse

• 2N spore mother cells undergo meiotic cell division (meiosis) to produce 4 genetically different 1N sexual spores

sexual reproduction in fungi

involves fusion of compatible nuclei usually at the tips of special hyphae (gametangia)

• a dikarytoic stage can exist temporarily prior to fusion of two haploid nuclei

groups of fungi

• chytridiomycota

• zygomycota

• glomeromycota

• ascomycota

• basidomycota

• microsporidia

Phylum Chytridiomycota

simplest fungi that were once classified as protists

• free living and saprophytic

• parasitic forms infect aquatic plants, animals and insects

• found in the anoxic rumen of herbivores

• produce zoospore with single, posterior, whiplash flagellum

• asexual and sexual reproduction

• many members degrade cellulose and certain

Phylum Zygomycota

• called zygomycetes

• most are saprophytes

• form coenocytic hyphae containing numerous haploid nuclei

• usually reproduce asexually by asexual spores that develop at the tips of aerial hyphae in sporangia or conidiophores

sexual reproduction in zygomycota

• requires compatible opposite mating types

• chemical cytokine production causing special hyphae to produce gametangia at tips

• hyphae grow into each other and gametangia fuse, forming an N + N zygote

• zygote undergoes mitotic cell division to become N+N zygosporangium

• in sporangium, N+N cells fuse to produce 2N spore mother cells which undergo meiosis to produce 1N sexual spores

R. stolonifer

• in genus Rhizopus, in phylum Zygomycota

• grows on surface of moist carbohydrate rich foods like bread

• hyphae spread quickly covering surface, as rhizoids absorb nutrients

• salon hyphae become new rhizoids

Ascomycota

• sac fungi

• found in freshwater, marine and terrestrial habitats

• red, brown, blue-green molds cause food spoilage

• some are human and plant pathogens

• some yeasts and truffles are edible

• all form asci (chambers where sexual spores are formed)

ascomycota yeast life cycle

alternates between 1N haploid and 2N diploid

• exist in opposite mating types a and alpha

• in nutrient rich, mitosis and budding occurs

• in nutrient poor, cells of opposite mating types fuse, nuclei fuse to form 2N spore mother cell in ascus

  • 2N spore mother cell undergoes meiosis to form ascospores

ascomycota filamentous form life cycle

• asexual reproduction

  • 1N haploid spore mother cells form at tips of conidia and each undergoes mitosis to form 2, 1N condiospores

• Sexual reproduction

  • Morphology of N+N fruiting body varies

  • Inside fruiting body (called ascoscrp) asci form

  • inside each ascus, N+N nuclei fuse to make 2N spore mother cell

  • each 2N spore mother cell undergoes meiosis to produce 4, 1N ascospores

  • ascospores released from ascocarp and can germinate to form new fungus

Claviceps purpura

• type of ascomycota

• parasite on higher plants

• ergotism

  • toxic condition from eating infected grain

  • due to lysergic acid diethyl amide (LSD)

human ascomycota pathogens

candida, blastomyces, histoplasma

aspergillus

type of asscomycota that causes aflatoxins and cancer

basidiomycota examples

• rusts

• shelf fungi

• puffballs

• toadstools

• mushrooms

basidiomycota reproduction

asexual

• fragmentation

sexual

• hype of opposite mating types fuse to produce N+N fruiting body (basidiocarp)

• on underside of basiodcarp, basidiocarp form

• at tips of basidia, N+N nuclei fuse to form 2N diploid spore mother cells

  • 2N diploid spore mother cells undergo meiosis to form 1N haploid basidiospore

  • basidospores are release at maturity from tips to basidia