EVOLUTION OF BLACK YEASTS - POSSIBLE ADAPTATION TO THE HUMAN HOST

Ascomycetous black yeasts show adaptations to a wide array of environm ental conditions. Dothideaceous black yeasts are mostly found on plant leaves, while among herpotrichiellaceous species there are numerous o pportunists on humans. Factors which are of ecological significance in clude the presence of melanin and carotene, formation of thick cell wa lls and meristematic growth, presence of yeast-like phases, presence o f additional forms of conidiogenesis, thermo- and osmotolerance, adhes ion, hydrophobicity, production of extracellular polysaccharides, side rophores and acidic or alkaline secondary metabolites. The potential p athogenicity of a species is partly determined by its natural ecologic al niche. Dothideaceous black yeasts are osmotolerant rather than path ogenic. Herpotrichiellaceous black yeasts probably have low competitiv e ability and are found in rather special niches as secondary saprophy tes, e.g., on bacterial mats, on other fungi or in poor environments. Some species possibly utilize animal vectors for dispersal.