Molecular taxonomy and systematics of yeasts.

Complete 18S rDNA sequence data of 30 ascomycetous and basidiomycetous yeasts and dimorphic fungi were included in the phylogenetic tree of the Asco- and Basidiomycota. Based on cell wall sugar data, urease activity and complete sequences of the 18S r-DNA three classes were suggested within the Ascomycota: Euascomycetes, Protomycetes and Hemiascomycetes. The genera Coniochaeta and Lecythophora are homogeneous and closely related with the Sordariales. In contrast the genus Hyphozyma appeared heterogeneous. Within the Stephanoascus clade three new Candida species isolated from the hindgut of termites or fruiting bodies of mushrooms were detected. Based on cell wall sugars (presence of galactose) this Candida species are candidates for a new genus. Similarly cell wall sugars (presence of fucose) and ribosomal DNA sequences suggest a new genus for Taphrina vestergrenii. Within the Basidiomycota three classes can be separated based on cell wall sugars and complete sequences of the 18S rDNA (Urediniomycetes, Ustilaginomycetes, Hymenomycetes). Representatives of the genus Rhodotorula can be found in two different classes (Urediniomycetes and Ustilaginomycetes). The yeast isolates of the agarics Asterophora lycoperdoides and A. parasitica are closely related with the genus Trichosporon, different from the genus Trichosporon they lack arthrospores. Based on ribosomal DNA sequences the yeast isolates from Asterophora can be excluded from the genus Cryptococcus. We have suggested the new genus Asterotremella.