Zygosaccharomyces bailii
| Zygosaccharomyces bailii | |
|---|---|
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| Z. bailii cells in Sabouraud medium (100x) | |
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Saccharomycetes |
| Order: | Saccharomycetales |
| Family: | Saccharomycetaceae |
| Genus: | Zygosaccharomyces |
| Species: | Z. bailii |
| Binomial name | |
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Zygosaccharomyces bailii Barnett et al., 1983 |
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| Synonyms | |
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Saccharomyces bailii (Lindner, 1895) |
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Saccharomyces bailii (Lindner, 1895)
Torulaspora bailii (Lindner) Kock.-Krat.
Saccharomyces acidifaciens (Thomas and Davenport, 1985)
Saccharomyces elegans (Thomas and Davenport, 1985)
Zygosaccharomyces bailii is a species in the genus Zygosaccharomyces. It was initially described as Saccharomyces bailii by Lindner in 1895, but in 1983 it was reclassified as Zygosaccharomyces bailii in the work by Barnett et al.
Spoilage resulting from growth of the yeast Zygosaccharomyces is widespread, which has caused significant economic losses to the food industry. Within this genus, Z. bailii is one of the most troublesome species due to its exceptional tolerance to various stressful conditions. A wide range of acidic and/or high-sugar products such as fruit concentrates, wine, soft drinks, syrups, ketchup, mayonnaise, pickles, salad dressing, etc., are normally considered to be shelf-stable, i.e. they readily inactivate a broad range of food-borne microorganisms. However, these products are still susceptible to spoilage by Z. bailii.
Z. bailii vegetative cells are usually ellipsoid, non-motile and reproduced asexually by multilateral budding, i.e. the buds can arise from various sites on the cells. During the budding process, a parent cell produces a bud on its outer surface. As the bud elongates, the parent cell’s nucleus divides and one nucleus migrates into the bud. Cell wall material is filled in the gap between the bud and the parent cell; eventually the bud is separated to form a daughter cell of unequal size.Z. bailii cell size varies within a range of (3.5 - 6.5) x (4.5 - 11.5) µm and the cells exist singly or in pair, rarely in short chain. It has been observed that the doubling time of this yeast is approximately 3 hours at 23 °C in yeast nitrogen base broth containing 20% (w/v) fructose (pH 4.0). In more stressful conditions, this generation time is significantly extended.
Besides the asexual reproduction mode, under certain conditions (e.g. nutritional stress) Z. bailii produces sexual spores (ascospores) in a sac called ascus (plural: asci). Normally, each ascus contains one to four ascospores, which are generally smooth, thin-walled, spherical or ellipsoidal. It should be mentioned that the ascospores are rarely observed as it is difficult and may take a long time to induce their formation; besides many yeast strains lose the ability to produce ascospores on repeated sub-cultures in the laboratory. On various nutrient agars, Z. bailii colonies are smooth, round, convex and white to cream coloured, with a diameter of 2 – 3 mm at 3 – 7 days. As the morphology properties of Zygosaccharomyces are identical to other yeast genera such as Saccharomyces, Candida and Pichia, it is impossible to differentiate Zygosaccharomyces from other yeasts or individual species within the genus based on macroscopic and microscopic morphology observations. Therefore, the yeast identification to species level is more dependent on physiological and genetic characteristics than on morphological criteria.
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