Endospore formation in Hanseniaspora pseudoguilliermondii: a key characteristics of the species

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In the course of a study on yeast diversity in Japan and Thailand, we isolated two yeast strains with bipolar budding patterns. Physiological and phylogenetic analysis suggested that these two strains were identical to Hanseniaspora pseudoguilliermondii. However, these strains produced hat-shaped ascospores and endospores, the latter of which was an unknown characteristic of the species. Endospores were produced on yeast extract–malt extract (YM) plates, though ascospores were produced on cornmeal agar of H. pseudoguilliermondii cultures. Endospores were formed in a twin-cell structure composed of a mother cell and a daughter cell, which did not separate after budding. Unlike the cell wall of the endospores, that of ascospore was stained with a chitin-specific stain. This was a feature distinguishing endospores and ascospores. Cell morphology of H. pseudoguilliermondii was compared with other species of the genus by observing their type strains. Other Hanseniaspora species did not show endospore formation under the same condition in which H. pseudoguilliermondii did. Therefore, the formation of endospores was considered to be a species-delimiting character of H. pseudoguilliermondii.