The phylogeny of species of the genus Issatchenkia Kudriavzev (Saccharomycetaceae) based on the partial sequences of 18S and 26S ribosomal RNAs

The ten strains of Issatchenkia species were examined for their partial base sequences of 18S and 26S rRNAs. In the 18S rRNA partial base sequences (positions 1451-1618, 168 bases), the strains of the species of the genus Issatchenkia were found to be not uniform phylogenetically. The calculated base differences numbered 5-0, The strains of Issatchenkia species examined had 3-1 base differences with the type strain of Pichia membranaefaciens. Especially, the type strain of Issatchenkia ovientalis, the type species of the genus Issatchenkia was found to be closely related phylogenetically to that of P. membranaefaciens. The calculated number of base differences was only one. The base sequences on the fingerprint segment were comprised of four bases (four kinds of AUAU, CCAU, AUAG, and ACAU), as found in P. membranaefaciens (ACAA). In the 26S rRNA partial base sequences, the calculated number of base differences was 8-0 (positions 1611-1835, 225 bases), and the calculated percent similarities were 61-80 (positions 493-622, 130 bases), within the genus Issatchenkia. Discussion was made phylogenetically and taxonomically, especially on the phylogenetic relationship between the type species of the genera Issatchenkia and Pichia and on a circumscription of the genus Issatchenkia.