The Wonderful World of Fungi

Before we wade in, let's see where we are, phylogenetically. Several groups of organisms known collectively as "slime molds" were once included in Kingdom Fungi, but since have been determined to be only distantly related to them. Some of these might end up in their own Kingdoms some day.

KINGDOM FUNGI What is a Fungus?

Along with bacteria, these are the most important DECOMPOSERS in the biosphere. They convert dead, organic matter into its inorganic components.

General Terminology

  • mycelium - the entire body of the fungus
  • hyphae - (singular, hypha) threadlike structures of which the mycelium is composed
  • thallus - another term for the mycelium; "body"
  • spore - haploid propagule produced via meiosis
  • sporangium - structure within which spores are produced (either sexually or asexually, depending on life cycle stage)

    General Facts

  • Fungi live as haploid hyphal masses for most of the life cycle
  • Classification is based upon the mode of sexual reproduction
  • Hyphae come in two complementary "mating types" generally called "+" and "-" (since they are not easily definable as male and female, to which "+" and "-" can be considered analogous.)
  • all species--whether free-living or parasitic--are absorptive heterotrophs: they secrete digestive enzymes onto their nutrient source (whether alive or dead) and absorb the digestive products of those enzymes' interactions with the nutrient source.
  • The main structural support in the cell walls is chitin. There is no cellulose present in Fungi except for one small, aberrant group (of chytrids)
  • Fungi lack true tissues, and are composed of threadlike hyphae.
  • Main storage carbohydrate is glycogen (as in animals), not plant starch
  • Some phyla are characteristically coenocytic (a mass of cytoplasm with multiple nuclei) without any physical separation of of the cytoplasm.
  • Other phyla are characteristically septate: the cytoplasm is divided into hyphal compartments by septa (walls). The cytoplasm within each compartment may still be multinucleate (coenocytic).

    Some interesting notes

  • Pathogenic/parasitc fungi have specialized hyphae called haustoria, which are used to invade the host's cells and create a nutrient pathway between fungus and host.

  • Fungi exist in different forms

    Major Fungal Taxa Fungal taxa have undergone a great deal of revision in recent years, and a currently accepted phylogeny can be seen here. We'll focus on only a few groups for now.

    These fungi retain primitive characters that may provide clues about fungal origins.

    A chytrid parasite, Batrachochytrium dendrobatidis, has been implicated in the recent large-scale extinctions of amphbians, worldwide. More on this later.

    Zygomycota - reproduce sexually via zygospores

    Ascomycota - reproduce sexually via ascospores

  • Each ascospore germinates and develops into a new, genetically unique + or - hypha.

    An old name you might hear: Deuteromycota (a.k.a., "Fungi Imperfecti")
    This form taxon was created to include fungi that have secondarily lost the ability to sexually reproduce. Molecular data have placed most of the former fungi imperfecti in Ascomycota.

    Like typical Ascomycetes, they reproduce asexually via spores called conidia borne on hyphal structures called conidiophores. Common examples are Penicillium and Aspergillis, which are now classified within the Ascomycota.

    Basidiomycota - reproduce sexually via basidiospores

    Glomeromycota - Vital to Ecosystems Mycorrhizae - "fungus roots"

    This is a symbiotic relationship between a fungus and a plant root. (What does each partner get out of the relationship?)

    Some of the most valuable edible organisms in the world are truffles, various species of mycorrhizal fungi.

    Symbiotic Fungi

    Be sure to review the different types of symbiosis.

  • There are predatory fungi

  • There are prey fungi

  • There are parasitic fungi

  • There are mutualistic fungi

    And don't forget the invaluable service fungi provide, along with bacteria, as the earth's major decomposers.

    And now, a moment of silence to fully appreciate the fungi.