chapter 24

Fungill Lecture 24 - Chapter 31: Fly Agaric (Amanita muscaria) - Thunder Bird Falls, Alaska, 5 July 2014

Opening Quote

  • Joshua 9:12 NIV
    • "This bread of ours was warm when we packed it at home on the day we left to come to you. But now see how dry and moldy it is."

Taxonomic Groups

Chytrids (Phylum Chytridiomycota)

  • Characteristics:
    • Most are unicellular.
Structure:
  • Hyphae and Mycelia:
    • Lack hyphae and mycelia but can form a body-like thallus and root-like rhizoids.

Zoospore

  • Definition:
    • A motile, asexual spore that is capable of swimming in an aquatic environment using flagella.
Characteristics of Zoospores:
  • Typically have one flagellum, though some may possess multiple flagella.
  • Function: Used to disperse and find hosts.

General Characteristics of Chytrids

  • Ecology:
    • Most are decomposers, but many are parasites or mutualists (none infect humans).
    • Ubiquitous in aquatic and terrestrial environments, including deep-sea hydrothermal vents.
    • Anaerobic species aid in digestion in sheep and cattle.

Chytridiomycosis

  • Definition:
    • A fungal infection in the skin of amphibians.
Causes of Chytridiomycosis:
  • Specifically caused by two species of Batrachochytrium.
  • Notable Impact: Caused a decline of 7% of amphibian species since the 1980s.

Zygote Fungi (Zygomycetes - Phylum Zygomycota)

  • Characteristics:
    • Most are multicellular.
    • Have hyphae; spores lack a flagellum.
Zygosporangium
  • Definition:
    • A thick-walled, diploid structure (2n) formed sexually from a zygote by the fusion of two haploid hyphal extensions (1n).
    • Zygosporangium and diploid zygospores (2n) are produced during harsh environmental conditions and can resist these conditions for years.
Zygospores
  • Diploid zygospores (2n) later germinate and release haploid spores (1n).
  • Process: Neighboring mycelia can fuse, leading to the fusion of haploid nuclei of opposite mating types.

Subphyla of Zygote Fungi

  • Zoopagomycetes:
    • Most are parasites or symbionts of animals.
  • Mucoromycetes:
    • Most are parasites or symbionts of other fungi or plants.
    • Examples include Fly Death Fungi (Entomophthora muscae) and Bonnet Mold (Spinellus fusiger).

Sac Fungi (Ascomycetes - Phylum Ascomycota)

  • Characteristics:
    • Most are multicellular and have hyphae.
    • Spores lack a flagellum; can reproduce asexually or sexually.
Conidiophore
  • Definition:
    • The tip of a hypha that produces asexual spores called conidia.
Asexual Reproduction in Sac Fungi
  • Reproduces via conidiospores including structures like the Penicillium phialide and Aspergillus vesicle.
Conidia
  • Singular form: conidium; can occur in clusters or long chains.
  • Can also play a role in sexual reproduction, as seen in Aspergillus fumigatus.
Ascocarp
  • Definition:
    • A diploid "sac" (2n) with reproductive structures, formed sexually by hyphae.
Types of Ascocarps
  • Shaped like a cup, flask, or sphere.
  • Examples include Cleistothecium, Perithecium, and Apothecium.
  • Asci: Each ascocarp contains millions of asci, with each ascus containing 4 or 8 ascospores (1n).

Mutualistic Associations

  • Approximately 40% of species of sac fungi form mutualistic associations with a green alga or cyanobacterium in lichens.
    • Examples include Brown-eyed Wolf Lichen (Letharia columbiana), Common Sunburst Lichen (Xanthoria parietina), Tree Lungwort (Lobaria pulmonaria), Oakmoss (Evernia prunastri), and Lace Lichen (Ramalina menziesii).

Club Fungi (Basidiomycetes - Phylum Basidiomycota)

  • Characteristics:
    • Most are multicellular and have hyphae.
    • Spores lack a flagellum and are the most conspicuous group of fungi.
Basidiocarp
  • Definition:
    • A large, haploid reproductive structure (1n), formed sexually, consisting of club-shaped diploid basidia (2n) that produce haploid basidiospores (1n).
Structure of Basidiocarp
  • Components include gills, cap, gill, and stipe (stalk), as well as basidia and basidium along with the spores.
Biodiversity in Club Fungi
  • Basidia typically located in gills on the ventral surface of the basidiocarp in many species, although not all species produce a basidiocarp.
Ecological Role of Club Fungi
  • Most are decomposers; some act as parasites or mutualists, as seen in figures like Tricholomopsis aurea.

Ecological Roles: Decomposition

  • Role of fungi in breaking down organic compounds, which releases nutrients into the environment.
  • Crucial in both Carbon (C) and Nitrogen (N) cycles that sustain life.

Ecological Roles: Mutualism

  • Many plants and insects host symbiotic fungi, which absorb nutrients from the host and provide benefits to them.
Benefits of Fungi to Plants
  1. Enhanced water and nutrient absorption.
  2. Enhanced stress tolerance to heat, drought, salt, or heavy metals.
  3. Enhanced resistance against herbivores or pathogens by producing toxins.
Benefits of Fungi to Animals
  • Serve as a protective shield from predators and pathogens, as in the example of stinkbug eggs.
  • Break down plant matter in intestines of mammals, including humans.
Leafcutter Ants and Fungi
  • Leafcutter ants farm a club fungus, which feeds on the leaves they provide.
  • Fungus provides the ants with nutrients at the tips of their hyphae.

Lichens

  • Definition:
    • A mutualistic partnership between a fungus and a photosynthetic green alga or cyanobacterium.
Components of Lichens
  • The fungal component drives structure and provides shelter for the photosymbiont (mostly sac fungi).
  • The photosymbiont component typically resides under the surface of the fungal body, supplying carbon and nitrogen compounds to the fungus, constituted by 90% green algae and 10% cyanobacteria.
Anatomy of a Lichen
  • Components include ascocarp of fungus, soredia, fungal hyphae, algal layer, and algal cells.

Mycorrhizae

  • Definition:
    • Fungi associating with the roots of plants, which facilitate nutrient absorption.
Associations
  • Hyphae at tips of plant roots greatly assist in water and nutrient uptake.
  • Overall prevalence: Mycorrhizae are found in 95% of plant species.

Parasitism in Fungi

  • Approximately 5% of fungal species are parasitic towards plants, destroying a significant proportion of agricultural crops.
Animal Parasitism
  • Less than 1% of fungal species parasitize animals.
  • Notable example: specific chytrids are significantly harming amphibian populations.
Human Pathogenic Examples
  1. Ringworm, jock itch, and athlete’s foot - caused by several species of sac fungi that feed on moist, dead skin.
  2. Oral thrush and vaginal candidiasis - caused by Candida spp. which may overgrow when the immune system is weakened.
  3. Valley fever - caused by Coccidioides spp., fungi from inhaled soil spores.

Human Uses of Fungi

  • Food Sources:
    • Mushrooms (club fungi), morels and truffles (sac fungi) are commonly consumed.
    • Yeast (sac fungi) utilized in bread production and alcoholic beverages.
Medicinal Applications
  • Fungi like Penicillium spp. are vital for antibiotics, such as penicillin.

Quiz Preparation

  • Study for a quiz over lectures 23-24 (Chapter 31).