Understanding Alcohol Tolerance in Wine Yeasts

Understanding alcohol tolerance in wine yeasts is important in order to develop tools to rectify sluggish and stuck wine fermentations and new commercial yeast strains with desirable sensory or process characteristics. In previous work, we have identified two potential mechanisms for alcohol tolerance including ones related to the composition of the yeast cell membrane and to the nutrient utilization efficiency of the strain. To understand these mechanisms, we further examined both potential effects. Specifically, we were able to find that the composition of the cell membrane changes significantly as fermentation temperature is raised or lowered. Using our high resolution methods for measuring membrane composition, we were also able to identify specific types of lipids in the cell membrane that are associated with lower ethanol tolerance (e.g. several phosphatidylinositol lipids) and higher ethanol tolerance (e.g. several phosphatidylcholine lipids). In this period, we also developed and used a method for measuring a wide range of metabolites inside and outside of yeast cells during fermentation. Our analysis shows that certain metabolic pathways like the pentose phosphate pathway and glycerol secretion are negatively correlated with cell growth and ethanol tolerance of these strains. These major results have allowed us to begin to identify targets for genetic manipulation of wine yeasts that should increase or decrease alcohol tolerance. We hope to actively initiate this part of the project prior to the completion of funding this year. The work completed as part of this grant has resulted in two papers (one published and the other in final revisions after review) with two more in preparation and a number of presentations at local and national meetings.