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General Microbiology II

Fungal Diversity

General Characteristics of Fungi

• Structure
  • eukaryotic- individual cells are typically larger and more complex than bacterial cells
  • dimorphic - unicellular (yeasts) or multicellular (molds ... mycelium that is a mesh of elongated filamentous hyphae that are frequently branched, with perforated septa between cells to ensure unimpeded movement of nutrients from one region of the mycelium to another) ... some fungi are dimorphic (change back and forth from yeast to mold)
  • chitin in cell walls of most, but some contain cellulose instead; protect the cytoplasm from osmotic pressure changes and provides cell shape
  • Membranes- glycerol-based phospholipids with ester linkages which form typical bilayer membranes
  • Ribosomes - 80S RNA/protein particles which are required for protein synthesis
• Genetics
  • chromosome - multiple, non-identical DNA molecules complexed with histones; the DNA contains the "blueprint" for all cell structure and activity in regions called genes
  • introns and exons are present in fungi, as they are in the typical eukaryote
  • gene exchange - recombination during meiosis generates diversity
• Reproduction - generally via modified hyphae that form reproductive spores
  • sexual - fusion of haploid nuclei leading to formation of spores
  • asexual
    • binary fission
    • budding - unequal binary fission
    • fragmentation of hyphal elements
      • arthrospores formed directly from hyphal fragmentation
      • chlaymdospores formed from directly hyphal fragmentation, but surrounded by a thick wall
    • spores - thick walls help them withstand dry, cold, low-nutrient conditions
      • sporangiospores - produced inside a sporangium
      • conidiospores - produced "naked" in "rows" on conidiophores
      • blastospores - spores produced directly from "mother" cell by budding
• Physiology
  • aerobic (some facultatively anaerobic, but none are anaerobic) organotrophs
  • absorptive nutrient uptake - these cells secrete digestive enzymes to break down macromolecules to their subunits, then internalize the subunits to derive energy and structural building blocks
  • most are mesophilic (20-35C optima); some are psychrophilic, some are mildly thermophilic
  • pH optimum near 5.5, but some grow at extremes of the pH range 2-9
• Habitat - generally prefer dark, moist habitats containing organic material
  • terrestrial or aquatic (some live in freshwater, others in marine, habitats)
  • symbiotes with plants (mycorrhizae) or algae or cyanobacteria (lichens)
• Importance
  • most saprophytic (decomposers); some are pathogenic for plants or animals
  • some are symbiotic, especially those that are the fungal component of lichens
  • important commercially in food production and spoilage, as well as pharmaceutical and industrual chemical production

Groups of Fungi (~100,000 species)

• Chytridiomycota - Chytridiomycetes or Chytrids
  • morphology - globe-shaped cells with rhizoids
  • reproduction
    • sexual - at maturity, the globe-shaped cells become sporangia which release motile spores; diploid zygote develops into new globe-shaped cell
    • asexual - mitosis
  • habitat/importance
    • saprophytic decomposers which grow in on decaying plants or animals, mainly in freshwater habitats (including mud)
    • parasitic - some infect living plants, animals and other fungi
• Oomycota - Oomycetes or "egg" fungi or water molds (distantly related to red algae)
  • morphology - finely branched hyphal filaments, with cellulose (not chitin) cell walls
  • reproduction
    • sexual - egg cell fertilized by sperm cell (or antheridium), diploid zygote develops into hyphae
    • asexual - motile (flagellated), diploid zoospores which develop into new hyphae
  • habitat/importance
    • Saprolegna, Achyla - saprophytic aquatic decomposers which grow as cottony masses on dead algae or small animals, mainly in freshwater habitats
    • parasitic - tobacco "blue mold" (Peronospora hyoscyami); late blight of potatoes (Phytophthora infestans); grape downy mildew (Plasmopara viticola); fish gills
• Zygomycota - Zygomycetes, zygosporangium-forming fungi (~600 species)
  • morphology - mycelial
  • reproduction
    • sexual reproduction via zygospores - very resistant to harsh conditions
    • asexual spores (sporangiospores) formed in sporangia at tips of aerial hyphae
  • habitat/importance
    • generally saprophytic decomposers in soil, important in plant decay
    • Rhizopus stolonifer (common bread mold) is used commercially to produce tempeh (from tofu), pharmaceuticals including anaesthetics, contraceptives, industrial alcohols, meat tenderizer, yellow dye for margarine
• Ascomycota - Ascomycetes, sac fungi (~35,000 species)
  • morphology - dimorphic (yeast or mycelium with septate hyphae)
  • reproduction
    • sexual spores are ascospores - formed in ascus (= sac)
    • asexual spores are conidiospores
  • habitat/importance - generally saprophytic decomposers in soil, but some are used for food and some are parasitic
    • helpful - Morchella esculenta (morels) and Tuber brumale (truffles) are edible; Saccharomyces (cerevisiae, carlsbergensis, ellipsoideus) used to make bread, beer, wine; Neurospora crassa genetics research tool (spoilage-inducing bread mold)
    • damaging (parasites, etc.) - Claviceps purpurea produces LSD, causes ergot of rye; Ophiostoma ulmi causes Dutch elm disease; Cryphonectria parasitica causes chestnut blight; Monilinia fruticola causes brown rot of stone fruits
• Basidiomycota - Basidiomycetes, club fungi, aka mushrooms (~30,000 species)
  • morphology - dimorphic (yeast or mycelium with septate hyphae and fruiting bodies we recognize as mushrooms, shelf fungi, puffballs, etc.)
  • reproduction
    • sexual spores are basidiospores - formed by the basidium (club-shaped structure at tip of hyphae; may be inside a fruiting body called a basidiocarp)
    • asexual reproduction - budding, fragmentation of the mycelium, and by production of conidiospores, arthrospores, or oidia (Coprinus lagopus)
  • habitat/importance - generally saprophytic decomposers in soil, but some are used for food and some are parasitic
    • helpful - Agaricus campestris bisporus is an edible mushroom
    • damaging (parasites, etc.) - Amanita phalloides is poisonous (produces phalloidin and alpha-amanitin); Cryptococcus neoformans, human pathogen; Puccinia graminis causes black stem wheat rust; Ustilago maydis - causes corn smut
• Deuteromycota - Deuteromycetes or fungi imperfecti (~30,000 species)
  • morphology - mycelial with septate (perforated), branched hyphae
  • reproduction
    • sexual cycle not yet observed, hence fungi imperfecti; when sexual cycle is discovered, they are moved into one of the other three higher fungal divisions
    • asexual spores are conidiospores and are produced on conidiophores
  • habitat/importance - generally saprophytic decomposers in soil, but some are used for food and some are parasitic
    • helpful - Penicillium chrysogenum, penicillin; Penicillium, cheese production (Gorgonzola, Camembert, Roquefort); Aspergillus, industrial acids, soy sauce
    • damaging - Microsporium, Trichophyton, Epidermophyton causes tineas; Candida albicans causes opportunistic infections; Histoplasma capsulatum causes histoplasmosis; Aspergillus flavus produces aflatoxin; Verticillium, plant wilt