Effect of halo-tolerance gene Hal5 on ethanol tolerance of Saccharomyces cerevisiae.

Hal5 gene is involved in halo-tolerance of Saccharomyces cerevisiae during high salt stress. Ethanol stress and high salt stress have similarities, as both decrease the availability of water for cells and strain the osmotic homeostasis across the cell membrane. The Hal5 over-expression strain of yeast has more ethanol tolerance, but the Hal5 null mutant strain also has more ethanol tolerance than the wild-type strain. Hal5 over-expression in this yeast strain may help in adaptation to ethanol stress by way of directly stabilizing the proteins (trk1-trk2) that are responsible for maintaining osmotic homeostasis. Dysfunction of Hal5 in the null mutant may result in increased trehalose, which also stabilizes proteins and increases ethanol tolerance in comparison to wild type, although not as much as over-expression of Hal5. In biochemical assays and FTIR, we observed an increase in trehalose in Hal5 mutant in comparison to the wild-type, as well as a further increase in response to ethanol stress. The ethanol stress increases ROS, protein carbonylation, and lipid peroxidation in all strains, but the Hal5 over-expression and Hal5 null mutation mitigate these adverse effects of ethanol stress.