Morphology and Modes of Reproduction
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.
Read more about this topic: Zygosaccharomyces Bailii
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