What are Fungi?

Fungi are eucaryotic organisms such as unicellular yeasts, multicellular molds, and macroscopic varieties such as mushrooms. The thallus or colony of mold consists of long filaments called hyphae through which dissolved organic matter is absorbed. When environmental conditions are suitable, the hyphae grow and intertwine and form a mass called mycelium. The portion of mycelium concerned with obtaining nutrients is called the vegetative mycelium; the portion concerned with reproduction is called reproductive or aerial mycelium. The aerial mycelium as the name implies, projects above the surface of the medium on which the fungus is growing and often bears the reproductive spores. Spores are of key importance in the fugal identification process.

Although classification of organisms has been and continues to be controversial, Fungi remain an identified kingdom agreed upon by most everyone. The kingdom Fungi includes the following 4 phyla.

Chytridiomycota
* Ecologically significant
* Contains 100 genera consisting of approximately 1000 species
* Most species are saprobes
* Some are plant pathogens (i.e. Synchytrium endobioticum, Olpidium brassicae, Urophlyctis alfalfae.)
* Present in both aquatic habitats and soils
* Most aquatic forms are found in fresh water
* Most species complete their life cycles in a few hours of days
* Easy to manipulate in pure culture
* Useful as experimental organisms
* Cause brown spot of corn, crown wart of alfalfa, and black wart of potatoes
* Parasitize mosquito larvae - may prove valuable as a biological control


Zygomycota
* Consists of 2 classes: Zygomycetes and Trichomycetes.

Zygomycetes:
* Zygomycetes can be isolated from soil, dung, fruits and flowers, stored grains, fleshy plant organs, mushrooms, invertebrates and vertebrates.
* Most grow and sporulate quickly in their natural habitats.
* Some are saprobes others cause considerable plant damage. (i.e. Some members of Rhizopus stolonifer may cause a soft rot condition in strawberries and sweet potatoes others.)
* Some species belonging to the Zygomycete class are human pathogens. (i.e. Absidia).

Ascomycota
* Occupy a broad range of habitats.
* Some are parasitic others are saprophytic.
* Some are plant pathogens that cause destruction of crop plants, timber and ornamental trees.
* Some genera are responsible for causing apple scab, brown rot of stone fruits, powdery mildews, foot rot of cereals, ear rot of corn, blue stain and many others.
* Some can be pathogenic to immunosupressed or immunocompromised individuals. (i.e. Coccidioides immitis)
* Some provide a huge array of metabolic processes and products. (i.e. Saccharomycetales used in baking, brewing and distilling industries, antibiotics.)

Basidiomycota
* Harmful as well as useful
* Some cause plant disease in various crops and forests.
* Destroys wood products including lumber, railroad ties, and landscape timbers.
* Some are human pathogens. (i.e. Filobasidiella neoformans)
* Some are cultivated for food. (i.e. Agaricus brunnescens, Lentinula edodes - the shiitake mushroom, Pleurotus spp. - oyster mushroom.)

For more detailed information on Fungi please refer to the following texts:
Introductory Mycology 4th edition by Alexopoulos, Mims and Blackwell
Diagnostic Microbiology 2nd edition by Konenman, Allen, Dowell and Sommers
Atlas of Clinical Fungi 2nd edition by deHoog, Gene and Figueras
© 2002 U.S. Micro Solutions, Inc.