What is a fungus?

A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores. The primary carbohydrate storage product of fungi is glycogen.Most fungi have a thallus composed of hyphae (sing. hypha) that elongate by tip growth

The fungal thallus consists of hyphae; a mass of hyphae is a mycelium.

Structure of fungi

The Characteristics of Fungi

Fungi are NOT plants

Hyphae = tubular units of constructionHeterotrophic by absorptionReproduce by sporesEcologically pivotal roles

HyphaeTubularHard wall of chitinCross walls may form compartments (± cells)MultinucleateGrow at tips

Heterotrophic by AbsorptionFungi get carbon from organic sourcesHyphal tips release enzymesEnzymatic breakdown of substrateProducts diffuse back into hyphae

Product diffuses backinto hypha and is used

Nucleus hangs backand “directs”

Modifications of hyphae

Hyphal growth

Hyphae grow from their tipsMycelium = extensive, feeding web of hyphaeMycelia are the ecologically active bodies of fungi

This wall is rigid Only the tip wall is plastic and stretches

Hyphal growth from spore

mycelium

germinatingspore

Reproduce by spores

Spores are reproductive cellsSexualAsexual

Formed:Directly on hyphaeInside sporangiaFruiting bodies

Amanita fruiting body

Pilobolus sporangia

Penicillium hyphae

Kingdom Fungi

Nutritional Type Chemoheterotroph

Multicellularity All, except yeasts

Cellular ArrangementUnicellular, filamentous, fleshy

Food Acquisition Method

Absorptive

Characteristic Features

Sexual and asexual spores

Embryo Formation None

Fungi are ancient

Major fungal lineages are ancient, perhaps emerging one billion years agoFungi were present before the emergence of animals and vascular plants

KINGDOM

CHARACTERISTIC EXAMPLE

     

Monera Prokaryocyte BacteriaActinomyces

Protista Eukaryocyte Protozoa

Fungi Eukaryocyte * Fungi

Plants Eukaryocyte PlantsMoss

Animals Eukaryocyte * ArthropodsMammals

Man

Hierarchical Classification

Kingdom Fungi Phylum Basidiomycota Class Basidiomycetes Order Agaricales Family Agaricaceae Genus Agaricus Species: Agaricus campestris L.

Fungus versus Fungi

“Fungus” is used inclusively for a heterogenous group of organisms that have traditionally been studied by mycologists “Fungi” refers to the organisms in the Kingdom Fungi, the true fungi, also called the “Eumycota”

How many species of fungi exist?

- 80,000 species of fungi described

- 1,700 new species described each year

How many species of fungi exist?

- 80,000 species of fungi described

- 1,700 new species described each year

Basic Characteristics and Life Cycles

Ascomycota (inc.Deuteromycetes)BasidiomycotaZygomycotaMitosporic Fungi (Fungi Imperfecti)

Ascomycota – “sac fungi”

Teleomorphic fungiProduce sexual and asexual spores

Sex. – asciAsex. – commonCup fungi, morels, trufflesImportant plant parasites & saprobesYeast - SaccharomycesSeptateMost lichens

A cluster of asci with spores inside

Basidiomycota – “club fungi”

Produce basidiospores and sometimes conidiosporesSex – basidiaAsex – not so commonLong-lived dikaryotic myceliaRusts & smuts – primitive plant parasitesSeptateMushrooms, polypores, puffballsEnzymes decompose woodMycorrhizas

SEM of basidia and spores

Zygomycota – “zygote fungi”

Conjugation fungiCoenocyticSex - zygosporangiaAsex - common

Produce sporangiospores and zygosporesHyphae have no cross wallsGrow rapidlyRhizopus, Mucor (opportunistic, systemic mycoses)Mycorrhizas

Fig 31.6 Rhizopus on strawberries

True FungiTrue FungiChytridiomycota – “chytrids”- Classified in CMR as true fungi (because of their molecular relationships)Simple fungiProduce motile sporesMostly saprobes and parasites in aquatic habitatsCould just as well be Protists

Fig 31.5 Chytridium growing on spores

True Fungi versus Slime MouldsTrue fungi:- those that are hyphal- possess cell walls throughout most of their life cycle - are exclusively absorptive in their nutrition.

Slime moulds:- those that do not form hyphae- lack cell walls during the phase that they obtain nutrients and grow- are capable of ingesting nutrients by phagocytosis.

So they are more common to Protista although they produce fruiting bodies like fungi.

- The most studied of them are the cellular slime moulds and the plasmodial slime moulds or Myxomycetes.