Understanding and Increasing Alcohol Tolerance in Wine Yeasts
The goal of our project is to measure the cell membrane composition of a wide range of wine yeasts and correlate this composition with strain characteristics such as growth and ethanol tolerance, thus developing a rational approach to strain modification. In this way, new strains can be constructed that are highly ethanol tolerant or ethanol tolerance can be introduced into existing strains with favorable flavor characteristics. To achieve these goals, we first identified a group of yeast strains representing a wide range of ethanol tolerances. We then took a 12-member subset of this group and did a preliminary examination of the growth characteristics and ethanol tolerance of these strains, confirming that we do, in fact, have a wide range of characteristics. We have nearly completed development of a new HPLC/mass spectrometer (LC/MS) assay for determining cell membrane composition, and are in the process of moving this assay over to a more sensitive instrument for quantification. The main classes of lipids in yeast membranes are well separated with this method. We used this assay, in its current state, to examine the membrane composition of two strains with fairly different ethanol tolerances at several points throughout small scale fermentations. We demonstrated that membrane composition does, in fact, change over the course of fermentation, and is also quite different for the different strains. In addition, our initial experiments have shown that ethanol tolerance may be a dual function of both membrane composition and nitrogen utilization efficiency.