Vanderwaltozyma osmotolerans sp. nov., a novel ascomycetous yeast species isolated from rotting wood and soil in Japan

Three yeast strains closely related to the genus <i>Vanderwaltozyma</i> were isolated from rotting wood (<i>Zelkova serrata</i>) and soil in Japan. Based on sequence analyses of the internal transcribed spacer (ITS1-5.8S-ITS2) region, the D1/D2 domain of the LSU rRNA gene and the mitochondrial <i>COX II</i> gene, together with physiological characterization, these isolates were determined to represent a novel species. The ITS and D1/D2 sequences of the three strains were nearly identical, differing only by a single nucleotide, and their physiological profiles were indistinguishable, supporting their conspecificity. Notably, the strains actively fermented d-glucose and d-fructose. They exhibited tolerance to high osmotic stress, being capable of growth in media containing either 10% sodium chloride with 5% glucose or up to 50% (w/v) glucose. Furthermore, under V8 agar culture conditions, they consistently produced four ascospores per ascus. Phylogenetic analyses based on ITS and LSU D1/D2 sequences clearly placed these strains within the genus <i>Vanderwaltozyma</i> but distinct from other known species. In addition, comparison of <i>COX II</i> gene sequences further supported their separation from related species. Based on these phylogenetic and phenotypic characteristics, we propose <i>Vanderwaltozyma osmotolerans</i> sp. nov. to accommodate these isolates. The holotype of <i>V. osmotolerans</i> sp. nov. is designated as NBRC 117259^T.