Antonie van Leeuwenhoek 73: 331–371, 1998. 331 © 1998 Kluwer Academic Publishers. Printed in the Netherlands. Identification and phylogeny of ascomycetous yeasts from analysis of nuclear large subunit (26S) ribosomal DNA partial sequences Cletus P. Kurtzman∗ & Christie J. Robnett Microbial Properties Research, National Center for Agricultural Utilization Research, Agricultural Research Ser- vice, U.S. Department of Agriculture, Peoria, Illinois 61604, USA (∗ author for correspondence) E-mail:
[email protected] Received 19 June 1998; accepted 19 June 1998 Key words: Ascomycetous yeasts, phylogeny, ribosomal DNA, systematics Abstract Approximately 500 species of ascomycetous yeasts, including members of Candida and other anamorphic genera, were analyzed for extent of divergence in the variable D1/D2 domain of large subunit (26S) ribosomal DNA. Divergence in this domain is generally sufficient to resolve individual species, resulting in the prediction that 55 currently recognized taxa are synonyms of earlier described species. Phylogenetic relationships among the ascomycetous yeasts were analyzed from D1/D2 sequence divergence. For comparison, the phylogeny of selected members of the Saccharomyces clade was determined from 18S rDNA sequences. Species relationships were highly concordant between the D1/D2 and 18S trees when branches were statistically well supported. Introduction lesser ranges of nDNA relatedness than those found among heterothallic species. Disadvantages of nDNA reassociation studies in- Procedures commonly used for yeast identification clude the need for pairwise comparisons of all isolates rely on the appearance of cellular morphology and dis- under study and that resolution is limited to the ge- tinctive reactions on a standardized set of fermentation netic distance of sister species, i.e., closely related and assimilation tests.