Increased diversity in the genus Debaryomyces from Arctic glacier samples

Ice from Arctic glaciers contains large populations of yeasts. We studied 38 isolates from this environment, which were initially identified as Debaryomyces sp. related to Debaryomyces hansenii by sequence analysis of the D1/D2 domains of 26S rDNA. An analysis of the distribution of mitochondrial DNA insertions in the nuclear genome showed that 25 of these isolates were related to, but distinct from, D. hansenii. Sequence analysis of the ACT1 gene of these 25 isolates revealed that they formed three different types of putative hybrids. In particular, 23 putative hybrids carried an ACT1 sequence identical to that of three Debaryomyces strains, CBS 790, CLIB 660, CLIB 949, previously classified as associated with D. hansenii and an ACT1 sequence of an undescribed taxon. The latter sequence displayed between 22 and 27 bp divergence (2.6-3.2 %) over 841 bp from sequences of closely related Debaryomyces sp., suggesting that this new taxon very likely represents a novel species for which no pure strain is available. Sequence comparisons of CBS 790, CLIB 660, and CLIB 949 with related Debaryomyces type strains also revealed an important sequence divergence. The putative hybrids described in this study could be differentiated from non-hybrid isolates and other Debaryomyces species on the basis of their use of a number of carbon sources.