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 Vanderwaltozyma were isolated from rotting wood ( Zelkova serrata ) 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 COX II 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 Vanderwaltozyma but distinct from other known species. In addition, comparison of COX II gene sequences further supported their separation from related species. Based on these phylogenetic and phenotypic characteristics, we propose Vanderwaltozyma osmotolerans sp. nov. to accommodate these isolates. The holotype of V. osmotolerans sp. nov. is designated as NBRC 117259 T .