FungiFungi

Level 1 Biological DiversityLevel 1 Biological Diversity

Jim ProvanJim Provan

Campbell: Chapter 31Campbell: Chapter 31

IntroductionIntroduction

Fungi are eukaryotesFungi are eukaryotes

Nearly all multicellular Nearly all multicellular (yeasts are unicellular)(yeasts are unicellular)

Distinguished from Distinguished from other kingdoms by:other kingdoms by:

NutritionNutrition

Structural organisationStructural organisation

GrowthGrowth

ReproductionReproduction

Absorptive nutrition enables Absorptive nutrition enables fungi to live as decomposers and fungi to live as decomposers and

symbiontssymbionts

Fungi are heterotrophs that acquire nutrients Fungi are heterotrophs that acquire nutrients by by absorptionabsorptionSecrete hydrolytic enzymes and acids to Secrete hydrolytic enzymes and acids to decompose complex molecules into simpler decompose complex molecules into simpler ones that can be absorbedones that can be absorbedSpecialised into three main types:Specialised into three main types:

SaprobesSaprobes - absorb nutrients from dead organic - absorb nutrients from dead organic materialmaterialParasitic fungiParasitic fungi - absorb nutrients from cells of living - absorb nutrients from cells of living hosts; some are pathogenichosts; some are pathogenicMutualistic fungiMutualistic fungi - absorb nutrients from a host, but - absorb nutrients from a host, but reciprocate to benefit the hostreciprocate to benefit the host

Extensive surface area and rapid Extensive surface area and rapid growth adapt fungi for absorptive growth adapt fungi for absorptive

nutritionnutrition

Basic structural unit of Basic structural unit of fungal vegetative body fungal vegetative body ((myceliummycelium) is the ) is the hyphahyphaExcept for yeast, Except for yeast, hyphae are organised hyphae are organised around and within food around and within food source:source:

Composed of tubular Composed of tubular walls containing walls containing chitinchitinProvide enormous surface Provide enormous surface area: 10cmarea: 10cm22 of soil may of soil may contain 1km of hyphae contain 1km of hyphae with 314cmwith 314cm22 surface area surface area

Fungal hyphae may be septate Fungal hyphae may be septate or aseptateor aseptate

Hyphae of Hyphae of septateseptate fungi fungi are divided into cells by are divided into cells by crosswalls called crosswalls called septaseptaHyphae of Hyphae of aseptateaseptate fungi lack cross walls fungi lack cross walls ((coenocyticcoenocytic))Parasitic fungi have Parasitic fungi have modified hyphae called modified hyphae called haustoriahaustoria, which , which penetrate the host penetrate the host tissue but remain tissue but remain outside cell membraneoutside cell membrane

Fungi reproduce by releasing spores Fungi reproduce by releasing spores that are produced either sexually or that are produced either sexually or

asexuallyasexually

Usually unicellular, haploid and of various Usually unicellular, haploid and of various shapes and sizesshapes and sizesProduced either sexually (by meiosis) or Produced either sexually (by meiosis) or asexually (by mitosis)asexually (by mitosis)

In favourable conditions, fungi generally clone In favourable conditions, fungi generally clone themselves by producing enormous numbers of spores themselves by producing enormous numbers of spores asexuallyasexuallyFor many fungi, sexual reproduction only occurs as a For many fungi, sexual reproduction only occurs as a contingency - results in greater genetic diversitycontingency - results in greater genetic diversity

Spores are the agent of dispersal responsible for Spores are the agent of dispersal responsible for geographic distribution of fungi:geographic distribution of fungi:

Carried by wind or waterCarried by wind or waterGerminate in moist places with appropriate substrataGerminate in moist places with appropriate substrata

Generalised life cycle of fungiGeneralised life cycle of fungi

SexualSexual

AsexualAsexual

Phylogeny of fungiPhylogeny of fungi

Division Chytridiomycota: chytrids Division Chytridiomycota: chytrids may provide clues about fungal may provide clues about fungal

originsorigins

Originally placed in Originally placed in Kingdom ProtistaKingdom ProtistaShare many Share many characteristics with characteristics with fungi:fungi:

Absorptive nutritionAbsorptive nutritionChitin cell wallsChitin cell wallsHyphaeHyphaeEnzymes / metabolismEnzymes / metabolism

Earliest fungi: evolved Earliest fungi: evolved from protists and from protists and retained flagellaretained flagella

Division Zygomycota: dikaryote Division Zygomycota: dikaryote structures formed during sexual structures formed during sexual

reproductionreproduction

Characterised by Characterised by dikaryotic dikaryotic zygosporangiazygosporangia

Mostly terrestrial - live in Mostly terrestrial - live in soil or decaying materialsoil or decaying material

Some form Some form mycorrhizaemycorrhizae, , mutualistic associations mutualistic associations with plant rootswith plant roots

Hyphae are coenocytic - Hyphae are coenocytic - septa only found in septa only found in reproductive cellsreproductive cells

Life cycle of the zygomycete Life cycle of the zygomycete Rhizopus stoloniferRhizopus stolonifer, a common , a common

bread mouldbread mould

Life cycle of the zygomycete Life cycle of the zygomycete Rhizopus stoloniferRhizopus stolonifer, a common , a common

bread mouldbread mould

Under favourable conditions, reproduces asexually:Under favourable conditions, reproduces asexually:Sporangia develop at tips of hyphaeSporangia develop at tips of hyphae

Mitosis produces hundreds of haploid sporesMitosis produces hundreds of haploid spores

In unfavourable conditions, sexual reproduction occurs:In unfavourable conditions, sexual reproduction occurs:Mycelia of opposite mating types (+ and -) for gametangia that Mycelia of opposite mating types (+ and -) for gametangia that contain several haploid nuclei walled off by the septumcontain several haploid nuclei walled off by the septum

Plasmogamy of gametangia occurs Plasmogamy of gametangia occurs dikaryotic dikaryotic zygosporangiumzygosporangium

Under favourable conditions, karyogamy occurs: diploid nuclei Under favourable conditions, karyogamy occurs: diploid nuclei immediately undergo meiosis producing haploid sporesimmediately undergo meiosis producing haploid spores

Zygosporangium germinates sporangium which releases Zygosporangium germinates sporangium which releases recombined haploid sporesrecombined haploid spores

Division Ascomycota: sac fungi Division Ascomycota: sac fungi produce sexual spores in saclike produce sexual spores in saclike

asciasci

Include unicellular yeasts Include unicellular yeasts and complex multicellular and complex multicellular cup fungicup fungiHyphae are septateHyphae are septateIn asexual reproduction, In asexual reproduction, tips of specialised hyphae tips of specialised hyphae form form conidiaconidia - chains of - chains of haploid asexual sporeshaploid asexual sporesIn sexual reproduction, In sexual reproduction, haploid mycelia of haploid mycelia of opposite mating strains opposite mating strains fusefuse

Life cycle of an ascomyceteLife cycle of an ascomycete

ASEXUALASEXUAL

SEXUALSEXUAL

MITOSISMITOSIS

Division Basidiomycota: club Division Basidiomycota: club fungifungi

Named after transient Named after transient diploid stage: diploid stage: basidiumbasidiumImportant decomposers Important decomposers of wood / plant materialof wood / plant materialInclude:Include:

Mycorrhiza-forming mutualistsMycorrhiza-forming mutualistsMushroom-forming fungiMushroom-forming fungiPlant parasites e.g. rusts and Plant parasites e.g. rusts and smutssmuts

Characterised by Characterised by dikaryoticdikaryotic mycelium that mycelium that reproduces sexually via reproduces sexually via basidiocarpsbasidiocarps

Life cycle of a mushroom-Life cycle of a mushroom-forming basidiomyceteforming basidiomycete

Life cycle of a mushroom-Life cycle of a mushroom-forming basidiomyceteforming basidiomycete

Haploid basidiospores grow into short-lived haploid Haploid basidiospores grow into short-lived haploid mycelia: under certain conditions, mycelia: under certain conditions, plasmogamyplasmogamy occurs occurs

Resulting dikaryotic mycelium grows forming Resulting dikaryotic mycelium grows forming mycorrhiza or mushrooms (basidiocarps)mycorrhiza or mushrooms (basidiocarps)

Mushroom cap supports and protects gills: karyogamy Mushroom cap supports and protects gills: karyogamy in the terminal, dikaryotic cells lining the gills in the terminal, dikaryotic cells lining the gills produces diploid basidiaproduces diploid basidia

Resulting basidium immediately undergoes meiosis Resulting basidium immediately undergoes meiosis producing four haploid basidiosporesproducing four haploid basidiospores

Asexual reproduction less common than in Asexual reproduction less common than in ascomycetesascomycetes

MouldsMoulds

Rapidly growing fungus Rapidly growing fungus with no sexual stageswith no sexual stagesMay develop into a May develop into a sexual fungus, producing sexual fungus, producing zygosporangia, zygosporangia, ascocarps or ascocarps or basidiocarpsbasidiocarpsMoulds with no known Moulds with no known sexual stage are known sexual stage are known as Deuteromycota or as Deuteromycota or imperfect fungiimperfect fungi::

PenicilliumPenicilliumFlavour for blue cheesesFlavour for blue cheeses

YeastsYeasts

Unicellular: reproduceUnicellular: reproduceAsexually by buddingAsexually by buddingSexually by producing asci or Sexually by producing asci or basidiabasidia

Saccharomyces cerevisiaeSaccharomyces cerevisiae is most important is most important domesticated fungus:domesticated fungus:

Baking and brewingBaking and brewingModel organismModel organism

Can cause problems:Can cause problems:RhodotorulaRhodotorula: shower curtains: shower curtainsCandidaCandida: “thrush”: “thrush”

LichensLichens

Symbiosis of algae with Symbiosis of algae with fungal hyphaefungal hyphaeThe alga:The alga:

Provides fungus with foodProvides fungus with foodMay fix nitrogenMay fix nitrogen

Fungus provides good Fungus provides good environment for growth:environment for growth:

Hyphal mass absorbs Hyphal mass absorbs minerals and protects minerals and protects algaealgaeProduces compounds that:Produces compounds that:

– shield algae from sunlightshield algae from sunlight– are toxic - prevents are toxic - prevents

predationpredation

Lichen reproductionLichen reproduction

Occurs as a combined Occurs as a combined unit or independentlyunit or independentlyFungi reproduce sexually Fungi reproduce sexually (usually ascocarps)(usually ascocarps)Algae reproduce Algae reproduce asexually by cell divisionasexually by cell divisionSymbiotic units Symbiotic units reproduce asexually by:reproduce asexually by:

Fragmentation of parentFragmentation of parentFormation of Formation of sorediasoredia: small : small clusters of hyphae with clusters of hyphae with embedded algaeembedded algae

MycorrhizaeMycorrhizae

Specific, mutualistic Specific, mutualistic association of plant association of plant roots and fungiroots and fungi

Fungi increase Fungi increase absorptive surface of absorptive surface of roots and exchange roots and exchange soil mineralssoil minerals

Found in 95% of Found in 95% of vascular plantsvascular plants

Necessary for optimal Necessary for optimal plant growthplant growth

Ecological impacts of fungiEcological impacts of fungi

Ecosystems depend on fungi as decomposers and Ecosystems depend on fungi as decomposers and symbionts: decompose food, wood and even symbionts: decompose food, wood and even plastics!plastics!Some fungi are pathogens e.g. athlete’s foot, Some fungi are pathogens e.g. athlete’s foot, ringworm etc.:ringworm etc.:

Plants particularly susceptible (e.g. Dutch elm disease)Plants particularly susceptible (e.g. Dutch elm disease)Ergot - affects cereal crops: causes gangrene, Ergot - affects cereal crops: causes gangrene, hallucinations and “St. Anthony’s fire”hallucinations and “St. Anthony’s fire”

Many animals, including humans, eat fungi:Many animals, including humans, eat fungi:In US, mushroom consumption restricted to In US, mushroom consumption restricted to AgaricusAgaricusWe eat a range of cultivated and wild mushroomsWe eat a range of cultivated and wild mushroomsTruffles are underground ascocarps of mycelia that are Truffles are underground ascocarps of mycelia that are mycorrhizal on tree rootsmycorrhizal on tree roots