Compost is decomposed plant debris prepared by gathering refuse material in a heap to hasten the decay of the material and reduce its bulk. The heat produced in the heaped mass of garbage, plant residues, herbivore dung and kitchen and municipal waste kills pests, mesophilic microorganisms and drives off toxic ammonia. The process of production of organic manure by composting is an unwitting exploitation of thermophilic microorganisms. A similar exploitation of thermophilic fungi is in the preparation of substrate for the cultivation of the edible mushroom Agaricus bisporus. A mixture of herbivore dung and straw is composted to give the material a physical texture that favors the growth of mushroom mycelium. Thermophilic fungi, in particular Scytalidium thermophilum (syn. Torula thermophila, Humicola grisea var. thermoidea, Humicola insolens), play a dominant role in the preparation of mushroom compost (Straatsma and Samson, 1993). The majority of the about 30 currently known species of thermophilic fungi were originally isolated from composts of various types.
Since composts are man-made environments, it is arguable whether they can be considered as natural habitats where thermophilic fungi evolved. Cooney and Emerson (1964) suggested that the nests of the incubator birds (mallee fowl), a species existing for 50 to 60 million years, as a possible natural habitat of thermophilic fungi. These are large-sized birds found in Australia and islands of the southwestern Pacific that gather forest litter and soil and construct large mounds inside which eggs are laid for incubation (http://www.abc.net.au/science/scribblygum/0ctober2000/default.htm). The interior temperature ranges from 33 to 50°C for several months. Perhaps such warm, humid and aerobic environments were sites where thermophilic fungi evolved from the mesophilic forms. The limited species diversity of thermophilic fungi suggests they are of relatively recent origin.
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