Hanseniaspora guilliermondii

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Hanseniaspora guilliermondii is a yeast in the family Saccharomycodaceae. In its active, asexual form it is called Kloeckera apis. The first sample was taken from an infected nail of a patient by Adrianus Pijper in 1928. For a while, scientists lumped it with Hanseniaspora valbyensis, but later work showed they are distinct. Other names that were tied to this species over time include H. melligeri, H. apuliensis, and Kloeckera apis, which were ultimately recognized as the same species.

Cells are small (about 2.2–5.8 μm by 4.5–10.2 μm), almond- to ovoid-shaped, and reproduce by budding from both ends. In broth, the cells settle and, after a month, a very thin ring can form. On malt agar at 25°C for a month, colonies are white to cream, glossy and smooth, with a slightly raised center. Pseudohyphae are weak or absent. It can produce one to four hat-shaped ascospores after at least a week on malt extract or potato dextrose agar; the ascospores tend to clump together.

Biologically, it ferments glucose but not galactose, sucrose, maltose, lactose, raffinose, or trehalose. It grows at 37°C but not at 40°C. It can grow in the presence of 0.1% cycloheximide and can use 2-keto-D-gluconate as its sole carbon source.

Ecologically, although the original sample came from a clinical setting, this yeast is mainly associated with fruits, plants, fermenting musts, and insects. Some strains produce acetoin, a compound found in many foods and fragrances.