The phylogenetic relationships of the saturn-shaped ascospore-forming species of the genus Williopsis Zender and related genera based on the partial sequences of 18S and 26S ribosomal RNAs (Saccharomycetaceae): the proposal of Komagataea Gen. Nov.

The partial base sequences of 18S and 26S rRNAs of strains of Williopsis and Saturnospora species were analyzed. In the three regions partially sequenced, the higher base differences were observed in the strains examined of the three species, W. californica, W. mucosa, and W. pratensis, compared with those of W. saturnus var. saturnus (type species of genus Williopsis), W. beijerinckii, W. mrakii, W. saturnus var. subsufficiens, W. suaveolens, P. membranaefaciens (type species of genus Pichia), C. matritensis (type species of genus Citeromyces), and S'spora dispora (type species of genus Saturnospora): the percent similarities were 52-82 in positions 493-622, 130 bases, of 26S rRNA, and the number of base differences was 28-6 in positions 1611-1835, 225 bases, of 26S rRNA, and the number of base differences was 25-4 in positions 1451-1618, 168 bases, of 18S rRNA. In the 18S rRNA partial base sequencings, W. mucosa had an identical base sequence with P. anomala (identical to H. anomala, type species of genus Hansenula). Based on the sequence data obtained, the taxonomic positions of the three Williopsis species mentioned above are discussed. The genus Zygowilliopsis Kudriavzev was postulated to be retained and emended, and a new genus, Komagataea was proposed for W. pratensis with a new combination, Komagataea pratensis.