Chapter 5.3 Fungal Biology Overview

Fungal Characteristics

• Fungi lack chlorophyll and cannot perform photosynthesis, unlike plants, which are autotrophic.
• Fungi are heterotrophic, obtaining nutrients from other sources, unlike plants.
• Fungi have cell walls made of chitin, not cellulose like plants.
• Fungi are eukaryotic, having a true nucleus and membrane-bound organelles, distinguishing them from prokaryotic bacteria.
• Fungal cell membranes contain sterols, while bacterial membranes do not.
• Fungi cell walls do not contain peptidoglycans as bacterial cell walls do.

Fungal Forms

• Fungi can exist as molds (multicellular, aerobic, reproduce by spores) or yeasts (unicellular, facultative anaerobes, reproduce sexually and asexually. Asexual reproduction methods include budding and transverse division).

Fungal Structures

• Hyphae: Thread-like filaments that absorb nutrients for the fungus. Branching hyphae allow the fungus to expand its surface area.
• Mycelium: The interwoven network of hyphae that forms the visible fungal body.
• Septate hyphae: Have cross-walls (septa) separating individual cells.
• Non-septate hyphae: Lack cross-walls, forming a continuous tube of cytoplasm.

Fungal Nutrition

• Saprotrophs: Decompose dead organic matter.
• Parasites: Obtain nutrients from a living host.
• Symbionts: Live in a mutually beneficial relationship with another organism (e.g., algae in lichens, plants in mycorrhizae).

Fungal Symbiotic Relationships

• Mycorrhizae: A symbiotic association between fungi and plant roots, where the fungi provide minerals and water, and the plants provide carbohydrates.
• Lichens: A symbiotic association between fungi and algae or cyanobacteria.

Fungal Classification

• Fungi are classified based on their dimorphism (two forms). This changes depending on:
  • Location: Within animal tissue (yeast) vs. outside plant/animal (hyphae) vs. inside plant (hyphae).
  • Temperature: Room temperature (hyphae) vs. high temperatures (yeast)
• Key fungal phyla to study: Chytridiomycota, Glomeromycota, Zygomycota, Ascomycota, Basidiomycota, Microsporidia. Each phylum has specific characteristics including septation (cross walls), mode of nutrient gathering, and reproductive strategies.

Fungal Reproduction

• Asexual reproduction: Fungi form spores, which germinate and produce new organisms genetically identical to the parent. This is a faster process compared to sexual reproduction.
• Sexual reproduction: Fusion of nuclei from two mating strains of the same species.

Fungal Phyla Details

• (see detailed information on each phylum in the initial text)*

Fungal Diseases

• Ergotism: A medieval European condition, caused by fungus, and sometimes used to induce abortion.
• Histoplasmosis ("Summer Flu"): Lower respiratory infection caused by Histoplasma capsulatum, often found in bat guano or soil. Inhalation of spores is the source of infection.
• Dermatophytosis ("Ringworm"): Fungal infection affecting skin, hair, and nails, caused by Trichophyton (nails) and Microsporum (scalp/skin). Characterized by blister-like lesions.
• Tinea pedis, corporis, cruris: Different forms of ringworm, affecting specific body regions.
• Candidiasis (Thrush/Yeast Infection): Caused by Candida albicans, resulting in vulvovaginitis (STD), oral thrush (inflammation of the mouth or throat).
• Coccidioidomycosis ("Valley Fever"): Respiratory infection caused by Coccidioides immitis and C. posadasii spores in dust. Causes hacking cough, chest pain, high fever, and is opportunistic.