Metabolic Analysis of Saccharomyces Cerevisiae to Evaluate the Relationship Between Nitrogen Utilization Efficiency and Ethanol Tolerance During Alcoholic Fermentation

During alcoholic fermentation, the sugar utilization activity of yeast cells decreases in the presence of alcohol, followed eventually by a loss in cell viability. Understanding ethanol tolerance should allow its modulation in yeast strains with other desirable characteristics.  Commercial yeast strains, given an identical initial nitrogen concentration and composition, will form different concentrations of biomass. Theoretically, strains that use nitrogen more efficiently to create more biomass will be able to tolerate higher levels of ethanol produced. The goal of this project is to understand the relationship between nutrient environment, nitrogen metabolism, and specific growth rate in Saccharomyces cerevisiae on a fundamental level, in order to develop a rational approach to strain modification for increasing ethanol tolerance. This will be achieved by determining the extracellular and intracellular concentrations of key metabolites in yeast collected during the exponential and stationary phases. Thirty-two commercial yeast strains were compiled with a wide range of growth and ethanol tolerance attributes. Nitrogen utilization efficiency and fermentation kinetic parameters were studied in each strain. Maximum optical densities for these yeast ranged from 2.68 to 6.17. A complete metabolic analysis will be performed to investigate the differences in carbon and nitrogen metabolism using supernatant and cell samples saved from fermentations using GC-MS.