Fungal Biology Summary

Overview of Fungi

  • Domain: Eukarya
  • Kingdom: Fungi
    • Diverse and widespread
    • Essential for terrestrial ecosystems; they decompose organic material and recycle vital nutrients

Key Characteristics of Fungi

  • Heterotrophic Nature:
    • Absorb nutrients (organic molecules) from their environment
    • Use exoenzymes to break down complex molecules into smaller organic compounds
    • Fungal lifestyles include:
    • Decomposers
    • Parasites
    • Mutualistic Symbionts

Fungal Morphology

  • Common structures include:
    • Multicellular Filaments
    • Single Cells (Yeasts)
  • Mycelium: Network of branched hyphae adapted for nutrient absorption
  • Fruiting Body: Reproductive structure where spores are contained for dispersal (e.g., mushrooms)
  • Cell Walls: Composed of chitin
Hyphal Structures
  • Septate Hypha: Divided into cells by cross-walls (septa), allowing organelles to move between cells
  • Coenocytic Hypha: Continuous cells with multiple nuclei
Modified Hyphae
  • Adaptations for special functions:
    • Trapping and Killing Prey
    • Haustoria: Extract nutrients from plants
    • Arbuscules: Facilitate nutrient exchange with plants (mycorrhizae - root-fungus association)

Fungal Reproduction

General Overview
  • Fungi reproduce via spores (in large quantities) through both sexual and asexual means
  • Most fungi are predominantly haploid with a short diploid stage during the sexual life cycle
    • Main steps include:
    • Meiosis → Production of haploid spores
    • No alternation of multicellular generations
Key Terminology
  • Plasmogamy: Fusion of cytoplasm from two parents
  • Heterokaryotic Mycelium: Nuclei from two parents present
  • Dikaryotic Mycelium: Each cell contains paired nuclei
  • Karyogamy: Fusion of nuclei from two parents
Asexual Reproduction
  • Yeasts reproduce by budding; molds produce haploid spores via mitosis

Fungal Diversity

  • Categories of Fungi:
    • Cryptomycetes: Over 30 species, diverse habitats
    • Microsporidians: 1300 species, unicellular parasites
    • Chytrids: Unicellular, aquatic, flagellated zoospores
    • Zoopagomycetes: 900 species, parasites or mutualists
    • Mucoromycetes: Fast-growing food molds, includes Rhizopus
    • Ascomycetes: Over 90,000 species; sac fungi, includes yeasts and molds
    • Basidiomycetes: Around 50,000 species; club fungi including mushrooms and shelf fungi
Ascomycetes and Their Importance
  • Produce spores in saclike asci
  • Fruiting bodies known as ascocarps
  • Examples include:
    • Neurospora crassa: Pink bread mold
    • Penicillium notatum: Source of penicillin
    • Saccharomyces: Brewer’s yeast
    • Pathogenic species such as Trichophyton (athlete’s foot)
Basidiomycetes Characteristics
  • Key features:
    • Club-like basidia and fruting body (basidiocarp)
    • Important for decomposing wood and plant material
Lichens
  • Symbiotic association between a photosynthetic organism (typically green algae or cyanobacteria) and a fungus (usually an ascomycete)
  • Photosynthetic cells embedded within a mass of fungal hyphae

Fungal Reproductive Life Cycle

  1. Two haploid mycelia from different mating types undergo plasmogamy.
  2. Formation of a dikaryotic mycelium that grows faster than parental mycelia.
  3. Environmental cues induce sporulation and fruiting body formation (e.g. basidiocarps).
  4. Basidia produce basidiospores through karyogamy and meiosis.
  5. Dispersal of basidiospores via wind, followed by germination into new mycelia.