The Assimilation of glucose by wine yeast under nitrogen limitation conditions

During fermentation of grape must, Saccharomyces cerevisiae growth arrest generally occurs when the medium still contains high sugar concentrations. At this stage of fermentation, a rapid inhibition of fermentative metabolism, is observed in some cases leading to sluggish or stuck fermentation. Nitrogen limitation has been identified as a contributing factor increasing the incidence of stuck fermentation. Nitrogen deficiency may have an impact on the ability to synthesize protective factors and lead to enhanced ethanol sensitivity. Furthermore, the absence of nitrogen may also weaken the yeast's ability to resynthesize ATPase which is lost during stationary phase. We used two different approaches to obtain mutants that efficiently utilize glucose under nitrogen limited conditions. 1) UV mutagenesis of wine yeast strains, VIN13 and K1 and 2) transposon mutagenesis of W303. By these approaches we obtained several wine yeast mutants which enhanced fermentation speed and we identified three genes which appear to enhance glucose utilization under nitrogen limiting conditions. We are currently further characterizing the mutant strains.