week 3

• Fungi


  Eukaryotic microorganisms including yeasts, molds and mushrooms
• As recently as 1960's fungi were referred to as being in the Kingdom Plantae
• Fungi


  • DO NOT obtain energy from the sun
  • DO NOT use CO2 as a carbon source
  • More closely related to humans than plants
• Fungi are of great importance both economically and socially
• Beneficial effects of fungi

  • Industrial fermentation
  • Bread, Alcohol, Cheese making (Stilton)
  • Antibiotics - penicillin
• Fungi are classified as a kingdom separate from plants and animals due to chitin in their cell wall
• Fungi


  • Provide essential support for all communities of multicellular organisms
• Morphology


  Fungi range in size from unicellular yeasts to large mushrooms and puffballs
• Yeasts


  • Unicellular, do not have flagella, and reproduce asexually by budding or traverse fission or sexually by spore formation
• Multicellular fungi


  • Have hyphae and mycelium
• Dimorphic


  Exist in two distinct forms, e.g. pathogenic yeasts have a yeast form in Human and a mycelial form in the environment
• Saprobic


  Fungi obtain nutrients from dead or decaying matter
• Fungi are unable to move but they very quickly colonise as a result of rapid rate that hyphae grow
• All fungi share a common pattern of reproduction in the form of spores
• Fungi cannot make their own food like plants do (from sunlight, water and CO2 using photosynthesis) as they have no chlorophyll
• Fungi


  • Secrete digestive enzymes and then absorb the broken down molecules from their environment
• Fungi


  • Grow hyphae with cell walls of chitin
• Chitin


  Beta-linked polymers of N-acetylglucosamine, a very strong material
• Hyphae


  • Grow by extending multinucleate cell filaments
  • May form septa partitioning the hypha into cells
  • Grow by cytoplasmic extension and branching
  • Branched mass of hyphae is called mycelium
• Hyphal compartments


  • Contain one or more nuclei (monokaryon and dikaryon forms)
  • Haploid small nuclei
  • Contain vacuoles, mitochondria, microbodies, oil droplets, glycogen
• Ergosterol


  Main sterol in the plasma membrane of fungi (cholesterol in animals and plants)
• Cell wall constitutes 20% of the cell weight and is a dynamic structure that changes in response to the environment
• Phyla of Fungi


  • Microsporidia
  • Blastocladiomycota
  • Neocallimastigomycota
  • Chytridiomycota
  • Glomeromycota
  • Ascomycota
  • Blasidiomycota
• Ascomycota and Basidiomycota


  • Subkingdom Dikarya (Higher fungi) with complex mycelium, perforate septa and complex life cycle
• Chytridiomycota


  Division of zoosporic organisms with motile asexual spores (zoospores)
• Zygomycota


  Fast growing fungi with primitive coenocytic (mostly aseptate) hyphae
• Asexual spores of Zygomycota

  • Chlamydoconidia
  • Conidia
  • Sporangiospores
• Factors affecting fungal growth

  • Temperature
  • Humidity
  • Light
  • Oxygen concentrations
  • Nutrients
  • Toxins
• Sporulation


  Production of spores when conditions for fungal growth become unsuitable
• Sporophores


  Structures that produce spores, useful for taxonomy
• Reproduction in Chytridiomycota


  • Asexual by formation of motile uniflagellate zoospores
  • Sexual by formation of diploid oospores
• Reproduction in Dikarya (Basidiomycota)


  • Rarely produce asexual spores
  • Much of life cycle as vegetative mycelium exploiting complex substrates
  • Sexual spore formation triggered by environmental conditions, forming fruit bodies (mushrooms and toadstools)
  • Diploid formation and meiosis occur in hyphal tip (basidium)
• Sexual spores


  • Chytridiomycota - zoospores
  • Zygomycota - zygospores
  • Ascomycota - ascospores
  • Basidiomycota - basidiospores
• Spore dispersal mechanisms


  • Passive liberation - stalked spore drop, rain splash
  • Active liberation - bursting of turgid cells, ballistospores
  • Climatic agents - wind, water
  • Animal dispersal
• Appendaged spores


  • Aid dispersal and attachment to substrates
• Active discharge


  Mechanism used by some fungi like Pilobolus to explosively discharge spores
• Motile spores


  Zoospores use flagella for locomotion, allowing them to move towards nutrients or oxygen