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Information

Candidial skin infection

Candida albicans

p. 556

Coccidioidomycosis

Coccidioides immitis

p. 591

Cryptococcal meningoencephalitis

Filbasidiella neoformans

p. 682

Histoplasmosis

Histoplasma capsulatum

p. 592

Pneumocytosis

Pneumocystis carinii

p. 754

Sporotrichosis

Sporothrix schenckii

p. 709

Vulvovaginal candidiasis

Candida albicans

p. 640

the protection and growing platform for the pair. In addition, the fungus absorbs water and minerals for the association. The photosynthetic member supplies the fungus with organic nutrients. It is possible to grow each partner of the lichen association separately. Usually the algal partner is able to grow well when separated, but the fungal partner does not. Because of this association, lichens can grow in extreme ecosystems where neither could survive on its own. Lichens are often a good indicator of air quality since they are very sensitive to sulfur dioxide, ozone, and toxic metals. You will not find very many lichens in cities with air pollution.

Mycorrhizae, fungal symbioses of particular importance, are formed by the intimate association between fungi and the roots of certain plants such as the Douglas fir. It is estimated that 80% of the vascular plants have some type of mycorrhizal association with their roots. There are more than 5,000 species of fungi that form mycorrhizal associations. By increasing the absorptive power of the root, they often allow their plant partners to grow in soils where these plants could not otherwise survive. With the world facing major shortages of food and forest products, a better understanding of these symbiotic relationships is urgently needed. Many trees, including the conifers, are able to live in sandy soil because of their extensive mycelial mycorrhizas. In Puerto Rico, for example, the pine tree industry almost perished before the proper fungi were introduced to form mycorrhizal relationships with the trees. Now the industry is flourishing. Similarly, orchids cannot grow without mycorrhizal association of a fungus that helps provide nutrients to the young plant.

Certain insects also depend on symbiotic relationships with fungi. For example, leaf cutter ants are estimated to bring about 15% of the tropical vegetation into their nests to use for food. The leaves are used as food by a fungus that the ants cultivate in their nests. The fungus removes the poison from the leaves of the plant, and then the ants use the fungus as their food source.

Economic Importance of Fungi

Many fungi are important commercially. The yeast Saccharomyces has long been used in the production of wine, beer, and bread.

Other fungal species are useful in making the large variety of cheeses that are found throughout the world. Penicillin, griseofulvin, and other antimicrobial medicines are synthesized by fungi.

Ironically, fungi are also among the greatest spoilers of food products, and large amounts of food are thrown away each year because they have been made inedible by species of Penicillium, Rhizopus, and others.

Fungi also cause many diseases of plants. Dutch elm disease caused by Ceratocystis ulmi is transmitted by beetles. It has destroyed the American elm trees that once shaded the streets in many cities. The wheat rust (Pucciniagraminis) destroys tons of wheat yearly. Rust-resistant varieties have been bred to reduce the losses, but mutations in the rusts have made these advantages short-lived.

Fungi have been very useful tools for genetic and biochemical studies. Neurospora crassa, a common mold, has been widely used for modern genetic studies as well as for investigating biochemical reactions. More recently, yeasts have been genetically engineered to produce human insulin and the human growth hormone somatostatin, as well as a vaccine against hepatitis B. ■ biotechnology, p. 219

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