Assimilation of Unusual Carbon Compounds

Abstract

Yeast taxa traditionally are distinguished by growth tests on several sugars and organic acids. During the last decades it became apparent that many yeast species assimilate a much greater variety of naturally occurring carbon compounds as sole source of carbon and energy. These abilities are indicative of a greater role of yeasts in the carbon cycle than previously assumed. Especially in acidic soils and other habitats, yeasts may play a role in the degradation of carbon compounds. Such compounds include purines like uric acid and adenine, aliphatic amines, diamines and hydroxyamines, phenolics and other benzene compounds and polysaccharides. Assimilation of purines and amines is a feature of many ascomycetes and basidiomycetes. However, benzene compounds are degraded by only a few ascomycetous yeasts (e.g. the Stephanoascus/ Blastobotrys clade and black yeastlike fungi) but by many basidiomycetes, e.g. Filobasidiales, Trichosporonales, red yeasts producing ballistoconidia and related species, but not by Tremellales. Assimilation of polysaccharides is wide-spread among basidiomycetes Growth tests on these compounds separate Trichosporon species that otherwise are hardly distinguishable. Yeasts able to degrade phenolics can be applied for cresol removal from polluted soil and styrene removal from air by biofilters containing black yeast. Yeasts growing on polysaccharides may be a valuable source of hydrolytic enzymes that can be applied in food technology. Biodegradative abilities of yeasts inhabiting aerial plant surfaces and the fate of these yeasts during anaerobiosis and lactic acid fermentation are also dealt with