The Wonderful World of Fungi

Kingdom Protista (fungus-like protists--slime molds)

Phylum Plasmodiophoromycota
Phylum Dictyosteliomycota
Phylum Acrasiomycota
Phylum Myxomycota

********************** The Fungus Among us

Kingdom Fungi: the True Fungi

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

Phylum Chytridiomycota
These are the most primitive of fungal taxa (they're the only ones that still have a flagellated life cycle stage, the zoospore), and may provide clues as to the origins of fungi. Most are aquatic

Some are saprobes, others are parasites of protists, plants and aquatic invertebrates.

Molecular data (DNA and RNA comparisons) also support the link between "chytrids" and other fungal taxa.

Phylum Zygomycota (black bread molds)

Phylum Ascomycota (sac fungi)

Phylum Basidiomycota (club fungi)

(Form Phylum) Deuteromycota (Fungi Imperfecti)

Formerly included in Kingdom Fungi:

What is a fungus?

1. absorptive heterotroph (a saprobe)

2. chitin in cell walls; no cellulose present, anywhere

3. no true tissues: the "body" of the fungus (THE MYCELIUM) is composed of threadlike structures called hyphae. The body of a fungus is also called a THALLUS, and is often used to refer to the fruiting body of the fungus--what we know as a "mushroom".

4. The main storage carbohydrate is glycogen (as in animals), not starch (as in plants)

5. Some phyla are characteristically COENOCYTIC; others are SEPTATE. (And if you didn't come to class, you'll just have to look up those terms for yourself.)

Some interesting notes on fungi:

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.

Different forms of fungus:

MOLD - rapidly growing, asexually reproducing hyphal fungus.

YEAST - a unicellular fungus, usually found growing in liquid or moist environments.

The three main phyla of fungi are distinguished on the basis of their mode of sexual reproduction:

ZYGOMYCOTA - reproduces sexually by producing zygospores.

Let's have a look at the typical life cycle of black bread mold....

  • Two haploid mating types (+ and -) meet and hyphae fuse (plasmogamy)
  • later, the nuclei inside the hyphae fuse (this is called karyogamy)
  • this forms in a diploid nucleus
  • A tough, walled structure called a ZYGOSPORANGIUM forms around the new nuclei.
  • Inside the ZYGOSPORANGIUM, the diploid nuclei undergo meiosis to produce haploid, genetically unique ZYGOSPORES.
  • Once released from the ZYGOSPORANGIUM, each ZYGOSPORE has the capacity to grow into a new + or - mycelium
  • Each new mycelium is genetically different from the original haploid parents.

    ASCOMYCOTA - reproduce sexually via ascospores.

    Let's have a look at the typical life cycle of sac fungi....

  • Two haploid mating types (+ and -) meet
  • the "-" mating type forms a structure called an ANTHERIDIUM ("male")
  • the "+" mating type forms a structure called an ASCOGONIUM ("female")
  • these two structures fuse, and the haploid nuclei of the antheridium enter the ascogonium.
  • the ascogonium grows into a mushroom like structure called an ASCOCARP
  • On special surfaces of the ASCOCARP, little saclike structures called ASCI (literally, "sacs") form.
  • Inside the asci, karyogamy occurs, with + and - nuclei fusing into diploid nuclei.
  • The new, diploid nuclei then undergo meiosis to produce genetically unique, haploid ASCOSPORES.
  • Once released from the ASCUS, each ASCOSPORE has the capacity to grow into a new + or - mycelium
  • Each new mycelium is genetically different from the original haploid parents!

  • ASCOMYCETE FUNGI CAN ALSO REPRODUCE ASEXUALLY BY BUDDING OFF ASEXUAL (mitotically produced) SPORES CALLED CONIDIA.

    BASIDIOMYCOTA - reproduce sexually via basidiospores.

    Let's have a look at the typical life cycle of club fungi....

  • Two haploid mating types (+ and -) meet
  • "+" and "-" hyphae fuse, and the haploid nuclei mingle. (plasmogamy again!)
  • the dikaryotic hyphae grow into a "mushroom" technically known as a BASIDIOCARP
  • On special surfaces of the BASIDIOCARP (e.g, the surfaces of the "gills" on the mushroom cap), "+" and "-" nuclei fuse (karyogamy) and little clublike structures called BASIDIA (literally, "clubs") form around them.
  • As the basidium undergoes meiosis to once again form haploid nuclei, the basidium develops and forms four appendages, each bearing a haploid BASIDIOSPORE
  • Once released from the BASIDIUM, each BASIDIOSPORE has the capacity to grow into a new + or - mycelium
  • Each new mycelium is genetically different from the original haploid parents!

    Form Phylum DEUTEROMYCOTA - This is a non-monophyletic grouping, and most members are simply ascomycetes that have secondarily lost the ability to sexually reproduce.

    They reproduce asexually via spores called conidia borne on hyphal structures called conidiophores.

    *************

    SYMBIOTIC FUNGI

    There are predatory fungi! (Arthrobothrys sp.)

    There are prey fungi! (We eat many species--but be sure you know what you're doing!)

    There are parasitic fungi! (See the scary samples Dr. Krempels is passing around!)

  • athlete's foot
  • fungi that inhabit warm, moist places (ew)
  • histoplasmosis (infects the lungs)
  • Dutch Elm disease threatens native U.S. populations of elm trees (it's carried by a bark beetle) (This is NOT the same as citrus canker (bacterial) or lethal yellowing of palm trees (viral).)
  • some fungi which infect rotting food (such as grain crops) can be carcinogenic (e.g., some species of Aspergillis or highly toxic (ascomycete ergots - a smut disease which infects plants). Ergots are sclerotia (resting stage of the fungus) which replace the ovaries (archegonia--you'll hear about them next time!) in the grasses they infect. These are loaded with highly toxic alkaloids which can cause central nervous system damage, smooth muscle contraction, necrosis, hallucinations and temporary insanity!).

  • There are mutualistic fungi! (These are the most fun. Unless you like melting flesh.) Lichens - a symbiotic association between a fungus and a photoautotroph.

    Found everywhere, but most notably are successful in harsh climates (dry, cold) where other organisms find it difficult or impossible to survive.

    Relationship: fungus provides a habitat for the algae (in an area where they could not otherwise survive) and the algae provide photosynthates for the fungus.

    * absorb nutrients directly from the atmosphere, and for this reason are very sensitive to smog.

    * important primary producers in harsh environment such as tundra.

    * original source of the compound used to make litmus paper.

    Mycorrhizae - "fungus roots"
    (Click on the highlighted word to see the diagram!)

    symbiotic relationships (usually mutualistic, sometimes commensal(?) ) between a fungus and a plant root.

    Vesicular Arbuscular Mycorrhizae (V.A.M.)

    association between a zygomycete and a plant

    Ectomycorrhizae

    association between asco or basidiomycete and a conifer or flowering plant (usually large trees).


    CAUTION: Do not click on the link below if have delicate sensibilities. No, really. I mean it. Fungi can also be terrible pathogens of plants and animals, as these images illustrate.