ABSTRACT
Below is a listing of the various yeast genera in alphabetical order, adapted from Lodder,22 including a brief discussion of those species thought to be of special interest. Where sufficient data are available, information on the range of base composition of nuclear deoxyribonucleic acid (expressed as mole % guanine + cytosine) is reported also. Data currently available indicate that for yeasts (in contrast to the higher fungi), organisms with a GC% greater than approximately 49% belong to the basidiomycetes, whereas those with less than about 49% are hemiascomycetes. Yeasts belonging to the imperfect fungi (Deuteromycetes) may represent either ascomycetous or basidiomycetous fungi and their range of %GC extends all the way from about 30 to 70%. In the borderline area (% GC ± 49%), when a sexual stage has not been demonstrated, decisions are not always possible with respect to a basidiomycetous or ascomycetous origin. Some support for one or the other may be gathered from the observation that basidiomycetous yeasts (as far as is known) usually produce urease when grown on urea and they have a laminated cell wall consisting of a number of layers, especially in older cells. Ascomycetous yeasts are normally urease negative and their cell wall consists of only two layers.21
