This study investigates how sugar-tolerant yeasts survive in environments with low water availability. Using Saccharomyces rouxii (sugar-tolerant) and Saccharomyces cerevisiae (non-tolerant) strains, researchers identified two key physiological differences: altered sucrose permeability and intracellular accumulation of polyols. Sugar-tolerant strains accumulated substantial amounts of polyols, primarily arabitol, making up approximately 18.5% of dry cell mass. These polyols were retained within cells even after washing, suggesting binding rather than passive osmotic accumulation. Notably, polyols were not detected in non-tolerant yeasts. Enzymatic assays showed that polyols function as compatible solutes—allowing enzymes to maintain activity under high solute concentrations—rather than serving merely osmotic purposes. This mechanism parallels how halophilic bacteria use potassium ions to tolerate high salt. The findings suggest polyols are synthesized and retained by sugar-tolerant yeasts as a physiological adaptation enabling survival at reduced water activity, representing a fundamentally different strategy from osmotic adjustment alone.

Key findings

• Sugar-tolerant yeasts accumulate intracellular polyols (primarily arabitol) constituting ~18.5% of dry cell mass, while non-tolerant yeasts do not contain detectable polyols
• Polyols function as compatible solutes maintaining enzyme activity under low water conditions, rather than serving purely osmotic roles
• Polyols are synthesized by sugar-tolerant yeasts and retained against concentration gradients, analogous to potassium accumulation in halophilic bacteria
• Sugar-tolerant and non-tolerant yeasts differ in sucrose permeability, with non-tolerant strains containing invertase that tolerant strains lack