Classifications of Fungi

Division Chytridiomycota

• Chytridiomycota: earliest fungi; evolved from protists and retained flagella

• Originally placed in Kingdom Protista

• Share many characteristics with fungi:

  • Absorptive nutrition

  • Chitin cell walls

  • Hyphae

  • Enzymes / metabolism

Zygomycota – “zygote fungi”

• Zygomycota: decomposers, pathogens, and some form mycorrhizal associations with plants

• Sexual Reproduction – zygosporangia: resistant to heat/cold and site of karyogamy

• Asexual reproduction: haploid spores

• Coenocytic

• Grow rapidly

Zygomycetes

• Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions

  • Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources

Ascomycota – “sac fungi”

• Ascomycota: important plant parasites & saprobes

• Sexual Reproduction – asci (sing. = ascus)

• Asex. Reprod: enormous numbers of asexual spores called conidia

  • Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores

• Cup fungi, morels, truffles

• Yeast - Saccharomyces

• Decomposers, pathogens, and found in most lichens

Division Basidiomycota: club fungi

• Basidiomycetes: important decomposers of wood / plant material

• Named after transient diploid stage: basidium

• Include:

  • Mycorrhiza-forming mutualists

  • Mushroom-forming fungi

  • Plant parasites e.g. rusts and smuts

• Characterized by dikaryotic mycelium that reproduces sexually via basidiocarps

Life Cycle of a Mushroom-Forming Basidiomycete

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

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

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

• Resulting basidium immediately undergoes meiosis producing 4 haploid basidiospores

• Asexual reproduction less common than in ascomycetes

Deuteromycetes

• Rapidly growing fungus with no sexual stages

• May develop into a sexual fungus, producing zygosporangia, ascocarps or basidiocarps

• Molds with no known sexual stage are known as Deuteromycota or imperfect fungi:

  • Penicillium

  • Flavor for blue cheeses

Yeasts

• Unicellular: reproduce

  • Asexually by budding

  • Sexually by producing asci or basidia

• Saccharomyces cerevisiae is most important domesticated fungus:

  • Baking and brewing

  • Model organism

• Can cause problems:

  • Rhodotorula: shower curtains

  • Candida: “thrush”

Mold

• Rapid growth

• Asexual spores

• Human importance:

  • Food spoilage

  • Food products

  • Antibiotics, etc.