Fungi and Yeast Notes

Kingdom Fungi Characteristics

  • General characteristics:
    • Eukaryotic organisms.
    • Non-vascular organisms.
    • Reproduce by spores (sexual and asexual).
    • Typically non-motile.
    • Exhibit alteration of generation.
    • Vegetative body: unicellular or composed of hyphae (microscopic threads).
    • Cell wall: similar to plants, composed of chitin.
    • Digest food first (exoenzymes), then ingest.
    • Store food as starch.
    • Chitin biosynthesis occurs in fungi.
    • Small nuclei.
    • Nuclear envelope does not dissolve during mitosis.
    • Nutrition: saprophytes, parasites, or symbionts.
    • Reproduction: sexual (teleomorph) and asexual (anamorph).

Division Ascomycota: Sac Fungi

  • Produce spores in cup-shaped sacs called asci.
  • Mature spores are ascospores, released when ascus breaks open.
  • Yeast: common unicellular fungi, reproduce asexually through budding.
  • Buds form at the side of the parent cell, pinch off, and grow into new yeast cells identical to the parent cell.
  • Examples: morels, truffles, cup fungi, powdery mildews, Aspergillus, Claviceps, Neurospora.

Yeast - Major Characteristics

  • Unicellular.
  • Eukaryotic.
  • Facultative anaerobes.
  • Capable of forming colonies on solid culture media.
  • Occur worldwide.
  • Over 1,500 species described.

Yeast - Reproduction

  • Asexual (most common) or sexual.
  • Asexual: budding or binary fission.
  • Sexual (if any): formation of spore structure.
  • Examples:
    • Saccharomyces cerevisiae
    • Schizosaccharomyces octosporus

Yeast Significance

  • Food Industry
    • Fermentation of bread, beer, and wine.
    • Saccharomyces cerevisiae (baker's yeast or sugar yeast).
  • Medical
    • Candida albicans: common in the human mouth but can cause candidiasis (oral/genital infection).
  • Biofuel Industry
    • Production of ethanol for car fuel.

Yeast - Taxonomy

  • Identified primarily by biochemical properties.
  • Found in 3 groups of fungi:
    • Ascomycotina
      • Examples: Saccharomyces cerevisiae and Schizosaccharomyces octosporus
    • Deuteromycotina
      • Examples: Trigonopsis, Rhodotorula, and Candida.
    • Basidiomycotina (no examples available in lab)

The three Deuteromycotina

  • Trigonopsis
    • Triangular cell morphology.
    • Budding yeast with buds arising at the apices.
      Rhodotorula
    • Orange/red pigmented colony morphology.
    • Budding yeast.
    • Rhodotorula glutinis
      Candida
    • Pseudohyphae formation (repeated budding where buds do not separate).
    • Opportunistic pathogen causing human infections.

Division Basidiomycota: Club Fungi

  • Includes mushrooms, puff-balls, smuts, rusts, and toadstools.
  • Spores borne on a club-shaped spore case called basidium.
  • In mushrooms, basidia are lined at the gills under the cap.
  • Huge numbers of spores produced (e.g., average mushroom produces over 16 billion spores).
  • Spores rarely germinate or mature.
  • Examples: Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).

Division Zygomycota: Zygote forming Fungi

  • Found on cheese, bread, and other decaying food.
  • Zygote forming fungi.
  • Spores produced in round-shaped case called sporangium.
  • Grayish fuzz on bread is mass of mature sporangia mold.
  • Under microscope, seen as pinheads.
  • When sporangium breaks open, hundreds of spores are released.
  • Example: Mucor, Rhizopus (the bread mold), and Albugo.

REPRODUCTION

  • Illustrations of yeast cell reproduction via developing bud, new bud, chain of buds.
  • Illustrations of zygomycota reproduction via sporangium, spores, germinating spore, stolon, rhizoids.

Economic Importance of Fungi

  • Recycling: Major role in recycling dead and decayed matter along with bacteria.
  • Food: Many mushrooms are used as food; edible species are cultured for sale.
  • Medicines: Penicillin antibiotic derived from Penicillium; many other fungi produce antibiotics.

Economic Roles of Fungi

  • Bio-control Agents: Fungi parasitize insects to control pests; sprayed on crops (cheaper, environmentally friendly).
  • Plant and Animal Diseases: Many fungi live on and in plants/animals causing diseases; can also co-exist harmoniously.
  • Food spoilage: Fungi play a major role in recycling organic material; fungal damage causes large losses of stored food (especially with moisture).
  • Production of beer and bread.