The Fungi

why do we care about fungi?

• decomposers

• producers of antibiotics

• microbiome (mycobiome)

• fermented foods

• pathogens

fungi basics

• the fungal body made of cytoplasmic filaments called hyphae

• a mass hyphae is called mycelium

• cell walls are made of chitin

• cells are haploid most of the time

• they use spores for reproduction

how do fungi consume their food?

• fungal body is adapted to feed by absorption

  • fungi digest their food externally by secreting digestive enzymes, then absorb that resulting organic molecules

  • mycelium (mass of hyphae) is the feeding structure of the fungus

  • most fungi are saprotrophs: they feed on dead or dying organic matter

saprotrophic fungi

decomposers. absorb their nutrients from dead sources (e.g. fallen logs or animal corpses). This allows for recycling of nutrients.

parasitic fungi

absorb their nutrients from living sources while providing nothing in return

mutualistic fungi

exchange benefits with another living organism in a mutually beneficial or symbiotic association

life cycle

• the fungus life cycle has both asexual and sexual parts

  • haploid structures are dominant in fungi

  • in sexual reproduction, the gametes are haploid hyphae (no female/male or eggs/sperm)

heterokaryotic

two un-fused nuclei from different parents in one cell

fungal sexual reproduction

• fertilization in fungi involves two steps: plasmogamy followed by karyogamy

  • plasmogamy is the union of two haploid parent cells without fusing the nuclei

    • in most fungi, the haploid nuclei from each parent do not fuse right away. instead, the two separate nuclei coexist in the cell’s cytoplasm. This stage is called heterokaryotic (n+n) 

  • karyogamy is the fusion of the two haploid nuclei in the heterokaryotic cell. this produces a diploid (2n) zygote

  • the diploid phase is short-lived: the zygote soon undergoes meiosis to produce haploid spores (n)

Mucoromycota

diverse group of fungi that includes many types of fungal molds

• includes the common bread mold rhizopus

• mostly saprotrophic, but some may be parasitic or form symbiotic associations

mucoromycota: rhizopus asexual structures

• sporangiophore and sporangia are specialized hyphae

• the sporangiophore bears a sporangium, which produces asexual spores by mitosis

• the spores disperse and germinate into hyphae

mucoromycota: rhizopus sexual reproduction

• rhizopus sexual reproduction is characterized by a diploid zygosporangium with a thick protective coat to survive adverse conditions

  • plasmogamy (fusion of hyphae cells without fusing the nuclei) produces heterokaryotic (n+n) zygosporangium

  • later, the young zygosporangium undergoes karyogamy (fusion of nuclei) to become a diploid (2n) zygosporangium

  • when conditions improve, the 2n zygosporangium undergoes meiosis to form a sporangiophore (n) and sporangium (n)

  • the sporangium produces many haploid spores (n) by mitosis

  • these spores are released and germinate into new hyphae 

ascomycota

ascomycota are considered the sac fungi

• includes yeasts (single celled fungi), cup fungi, truffles, morels, ergot, penicillium

• includes saprotrophs, parasites, and mutualistic fungi

ascomycota: asexual reproduction

• penicillium

  • penicillium has specialized hyphae called condiophores

  • mitotic division on the tips results in chains of asexual spores called conidiphores

• yeast

  • yeast reproduce asexually by budding

ascomycota: penicillium asexual reproduction

• conidiophores: specialized hyphae for asexual reproduction

• conidia: chains of asexual spores

ascomycota life cycle

• sexual reproductive structures

  • ascocarp: fruiting body 

  • ascospores: sexual spores

  • asci: spore-bearing cells

• each ascocarp contains millions of asci

basidiomycota

• basidiomycota are considered the club fungi

  • include mushrooms, puffballs, shelf fungi, and smuts

  • includes saprotrophs, parasites, and mutualistic fungi

  • have club shaped sexual structures called basidia that produce sexual basidiospores

  • they do not produce asexual spores

basidiomycota (parts)

• basidiocarp: fruiting body

• basidia: spore-producing cells

• gills or pores: site of basidia

some mushrooms have pores

bracket fungi lack gills

• the lower surface is composed of numerous tiny pores (instead of gills) through which large numbers of spores are released

symbiotic relationships with fungi

• fungi have formed mutually beneficial symbiotic relationships with photosynthetic organisms for at least 600 million years!

  • mycorrhizal associations:

    • mutually beneficial relationships between fungi and plants

  • lichens

    • mutually beneficial relationships between fungi and cyanobacteria or green algae

mycorrhizal fungi

• underground hyphae enmesh with plant roots in a mutually beneficial association

• 90% of all plant species form mycorrhizal association

• mycorrhizae = “fungus root”

  • fungus helps plant by improving water & nutrient uptake; also protects plant against pathogenic organisms

  • plant provides fungus with carbohydrates from photosynthesis

  • one mycelium can attach to multiple plants, transferring carbon from plant to plant (mycorrhizal network)

ectomycorrhizae

enmesh around root cortex but do not penetrate inside cells

• ascomycota or basidiomycota

endomycorrhizae

penetrate inside the root cells

• mycoromycota

lichens

lichens are a symbiotic association between fungi (mostly ascomycota or basidiomycota) and green algae or cyanobacteria 

• fungi provide: physical structure, protection, and enzymes that aid in mineral absorption

• green algae or cyanobacteria provide: photosynthesis, produces carbohydrates to support fungal growth

crustose lichens

foliose lichens

fruticose lichens

lichen cross section

asomycota: sordaria sexual reproduction