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.