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A class of the subdivision Deuteromycotina comprising anamorphic (asexual or imperfect) yeast fungi that lack fruit bodies (conidiomata), have no dikaryophase, and are usually unicellular rather than filamentous. The thallus consists of individual cells. Approximately 80 genera comprising about 600 species are recognized.
The Blastomycetes, like other groups of deuteromycetes, are artificial, composed entirely of anamorphic fungi of ascomycete or basidiomycete affinity. Taxa are referred to as form genera and form species because the absence of sexual, perfect, or meiotic states forces classification and identification by artificial rather than phylogenetic means. Black yeasts are distinguished from anamorphic yeasts by the presence of melanin in the cell walls, abundant production of septate mycelium (filamentous), and aerial dispersal of conidia. Unlike other deuteromycetes, the number of morphological and developmental features for classification of Blastomycetes, although useful, is limited. The emphasis in yeast systematics has therefore been on physiological and biochemical tests, supplemented extensively by serological, electrophoretic, and molecular techniques.
Anamorphic yeasts can be recovered from most ecological niches—animals, plants and their surfaces, fresh and marine water, soils, and environments such as manufacturing plants, tanning fluids, and mineral oils. Blastomycetes are of great economic importance in two respects: the production of products and the spoilage of raw materials and products. Selected strains of Saccharomyces cerevisiae are used in the baking, brewing, distilling, and wine industries.
Blastomycetes are also recognized pathogens in medicine. Both Candida, causing candidiasis or candidosis, and Cryptococcus, causing cryptococcosis, are opportunistic pathogens that cause systemic infections only in individuals with lowered resistance. Esophageal candidiasis and cryptococcosis of the central nervous system are both regarded as being particularly strong indicators of AIDS. See Deuteromycotina, Eumycota, Fungi, Yeast