Analysis of the Effects of Hyperosmotic Stress on the Derepression of Invertase Activities and the Growth of Different Baker's Yeast Strains

The growth of baker's yeast Saccharomyces cerevisiae in medium containing sucrose requires a high level of extracellular invertase enzyme activity. However, the expression of invertase is under the strict control of glucose repression in S. cerevisiae. In addition, invertase enzyme activity is also affected by physiological stress conditions that baker's yeast is exposed to during the various stages of industrial level production and downstream processing. We analyzed the effect of hyperosmotic stress on the derepression of invertase activities of a haploid laboratory yeast strain and three different industrial baker’s yeast strains. Our results indicated that hyperosmotic stress interferes with the derepression of invertase activity in the yeast. The invertase activities of the yeast strains remained essentially at a repressed level in the presence of 1M NaCl or 1M KCl in the growth medium. However, the presence of low amounts of NaCl in the growth medium (0.2M) increased the invertase activities of yeast strains up to 40-50%. We also found that industrial yeast strains are more sensitive to hyperosmotic stress than the laboratory strains of S. cerevisiae used in this study.