General Facts

Some interesting notes

• MOLD - rapidly growing, asexually reproducing hyphal fungus.
• YEAST - a unicellular fungus, usually found growing in liquid or moist environments.

Tiptoe through the Taxa Several major groups of fungi are generally recognized...

• Phylum Chytridiomycota (the "chytrids")
• Phylum Zygomycota (the black bread molds)
• Phylum Ascomycota (the sac fungi)
• Phylum Basidiomycota (the club fungi)

In addition, a FORM Phylum is sometimes used for convenience:

• "Phylum" Deuteromycota (the asexual fungi)
  These are probably all ascomycota which have secondarily lost the ability to reproduce sexually. Included are such economically important forms as Penicillium (the original source of penicillin and its derivatives) and Aspergillis (the original source of ascorbic acid, an agent widely used commercially to give tangy flavor to a wide variety of foods.

Let's meet the Fungi!

Phylum Chytridiomycota
These are the most primitive of fungi, and may provide clues as to the origins of fungi.

• Most are aquatic, suggesting an aquatic origin of Kingdom Fungi.
• Some are saprobes, others are parasites of protists, plants and aquatic invertebrates.
• Like all fungi, they have chitin in the cell walls
• one aberrant group or Chytrids has cellulose in the cell walls--UNIQUE among fungi
• They have flagellated gametes (zoospores)--a PRIMITIVE character not shared by any other true fungi
• Molecular data support the link between chytrids and other fungal taxa.

Phylum Zygomycota - reproduce sexually via zygospores

• reproduction is via fusion (plasmogamy) of + and - hyphae
• at the junction of the hyphae, a ZYGOSPORE is formed
• fusion of the + and - haploid nuclei (karyogamy) results in formation of diploid zygotes inside the zygospore
• still inside the zygospore, the zygotes undergo meiosis to produce genetically new, haploid spores.
• these are released, and will germinate to become genetically new + and - hyphae.

Phylum Ascomycota - reproduce sexually via ascospores.

• The + and - hyphae fuse to produce a DIKARYOTIC region of cytoplasm.
• This dikaryotic cytoplasm proliferates, with each haploid nucleus dividing and multiplying independently until...
• The dikaryotic hyphae develop into a fruiting body known as an ASCOCARP.
• The ascocarp bears specialized cells (called asci, because they resemble little sacs) in which karyogamy occurs.
• The diploid asci then divide meiotically to produce genetically unique ASCOSPORES.

Phylum Basidiomycota - reproduce sexually via basidiospores.

• The + and - hyphae fuse to produce a dikaryotic region, which proliferates and grows, with each haploid nucleus dividing and multiplying independently until...

• The dikaryotic hyphae grow into a fruiting body known as an BASIDIOCARP.
• The basidiocarp bears specialized cells (basidia) in which karyogamy occurs.
• The basidia then divide meiotically to produce genetically unique basidiospores.
  
• Each spore germinates to develop into a genetically unique + or - hypha.

Form Phylum DEUTEROMYCOTA ("Fungi Imperfecti") - This artificial taxon is not monophyletic. Most members are simply ascomycetes that have secondarily lost the ability to sexually reproduce.

Like Ascomycetes, they reproduce asexually via spores called CONIDIA borne on hyphal structures called conidiophores.

SYMBIOTIC FUNGI

• Arthrobothrys (a Deuteromycete) nabs nematodes

We eat many species--but be sure you know what you're doing!

• 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 or lethal yellowing of palm trees, both of which are 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 of infected grasses. These are loaded with highly toxic alkaloids which can cause central nervous system damage, smooth muscle contraction, necrosis, hallucinations and temporary insanity!).
• If you are not of delicate sensibility, click HERE to show what fungus can do to an immunosuppressed person.

• There are mutualistic fungi
  • Lichens - a symbiotic association between a fungus and a photoautotroph.
    • Lichens are found almost 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 (or cyanobacteria) (in an area where they could not otherwise survive) and the algae provide photosynthates for the fungus.
    • Lichens are very effective at absorbing nutrients directly from the atmosphere, and for this reason are very sensitive to smog.
    • Lichens are important primary producers in harsh environments such as tundra.
    • Lichens are the original source of the compound used to make litmus paper (an old-fashioned way to tell if a solution is acidic or basic).

  Mycorrhizae - "fungus roots"

  • This is a symbiotic relationship 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).