Comparative study of physiological adaptation to salt stress in the genome shuffled Candida versatilis and a wild-type salt-tolerant yeast strain

Candida versatilis is a yeast with a complex salt-tolerant system. It can maintain normal physiological activities and metabolic fermentation under a high-salt environment. The cellular mechanisms of adaptation to salt stress in strains of a wild type of C. versatilis (WT) and S3–5, genome shuffling strains of C. versatilis with improved tolerance to salt, were investigated. The content of intra- and extra-cellular glycerol, intra-cellular Na⁺, as well as membrane fluidity and permeability, were determined under salt-stressed yeast growth conditions. The results showed that Na⁺/H⁺-antiporter played a primary role in Na⁺ extrusion and H⁺-ATPase has been associated with yeast survival under salt stress. Considerable amounts of glycerol were produced and secreted by the yeast to outside the cell under this salt stress. Changes in the portion of membrane saturated and unsaturated fatty acid composition of C. versatilis in response to osmotic stress lead to membrane permeability and fluidity decreases. They could restrict the influx of Na⁺, enhance H⁺-ATPase activity, and prevent leakage of glycerol across the cell membrane under osmotic stress. The salt tolerance of genome shuffled strain S3–5 was higher than WT. It could be correlated with a higher level of intra-cellular accumulation of glycerol and sodium ions in cells of S3–5 than WT as well as a higher portion of oleic fatty acid (C18: 1) and a lower level of linoleic acid (C18: 2) in cell membranes of the studied yeast mutant. It can be concluded that S3–5 improved physiological regulatory mechanisms of response to salt stress, such as decreased membrane fluidity and a permeability that rapidly adjusted to osmotic stress.