Abstract
In order to clarify the phylogenetic relationships among the yeast species classified in the genus Saccharomyces, partial base sequences of 18S and 26S ribosomal RNAs were determined for ten selected strains. The regions determined correspond to positions 1451 through 1618 of the 18S rRNA and positions 493 through 622 and 1611 through 1835 of the 26S rRNA in S. cerevisiae. Analyses of these partial base sequences suggested that the genus Saccharomyces is phylogenetically heterogeneous. Saccharomyces servazzii and S. unisporus showed identical or very similar sequences in all the three regions, and their phylogenetic distance from S. cerevisiae was large enough to introduce a genus independent of Saccharomyces. Saccharomyces kluyveri is also distant from all the other Saccharomyces species examined, and is likely to deserve a new genus. Estimated phylogenetic relationships between Saccharomyces and other genera characterized by the Q-6 system, such as species of Zygosaccharomyces, Torulaspora, Kluyveromyces, Arxiozyma, Pachytichospora, Nadsonia, Hanseniaspora, Kloeckeraspora, and Saccharomycodes, are also discussed.
