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 did an in-depth examination of the growth characteristics and ethanol tolerance of these strains, and confirmed that we do, in fact, have a wide range of characteristics. We have completed development of a new HPLC-mass spectrometer (LC-MS) assay for determining cell membrane lipid composition. The main classes of lipids in yeast membranes are well separated with this method, and we are able to quantify over 80 species of fatty acids making this significantly higher resolution than the traditional methods for lipid analysis that have been used previously in studies on Saccharomyces. We are nearly finished with the associated assay for sterols. We used this assay, in its current state, to examine the membrane composition of six of the strains with fairly different ethanol tolerances from a point during small scale fermentations. These data were used, along with multivariate statistical approaches (e.g. Principal Component Analysis), to begin to examine how membrane composition varies with fermentation properties and ethanol tolerance levels. Studies to examine yield of cells from nitrogen were also initiated.