Osmotic Shock Augments Ethanol Stress in Saccharomyces cerevisiae MTCC 2918

Yeast cells sense and respond to hypertonicity. Saccharomyces cerevisiae MTCC 2918 was tested for its metabolic status in 1 M NaCl by cell viability analysis, intracellular glycerol content and total antioxidant capacity. Yeast cell viability was maximum in 1 M NaCl and 24 h addition of 1 M NaCl was effective in induction of hyperosmolarity. Increased glycerol contents in cells treated with salt indicated adaptation to osmotic stress with a maximum of 240.87 ± 0.38 mg/g dry weight (DW) at 72 h. The total antioxidant status with 1 M NaCl was 9.29 ± 0.39 mM/g DW at 96 h reflecting free radical quenching to overcome stress with increasing growth period. Considering that pre-adaptation to one type of stress evoked a protective response to other stress factors, we have attempted the cross adaptation of osmotic shock to high ethanol concentrations. In effect, we observed that osmotic shock lowered the cell survival by augmentation of cell toxicity by ethanol due to stress induction during exponential phase. Glycerol accumulation to an order of 470.27 ± 0.53 mg/g DW at 48 h in 1 M NaCl and 12% ethanol indicated that both stresses culminated in membrane disruption further leading to cell burst and contributed to the stress overload.