Functional characterization of genes required for yeast fitness during fermentation

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The unicellular yeast Saccharomyces cerevisiae (S. cerevisiae) is a model organism for understanding conserved cellular processes and is also a key microorganism for industrial food production. The modern S. cerevisiae genome has evolved to withstand the harsh environmental conditions of wine fermentation. However, most studies of S. cerevisiae gene function are performed in relatively benign laboratory conditions and as a result, 15% of yeast genes still have no known function. The changes to cellular metabolism that enable survival of yeast during fermentation are also poorly understood. My lab has assessed the growth of all nonessential S. cerevisiae genes during grape juice fermentation. We have discovered that autophagy (literally, "self-eating"), a process whereby cells engulf their own cytoplasm and recycle unwanted organelles for reuse of essential nutrients, is important for cellular fitness during fermentation. A number of other genes either positively or negatively affect cell survival under fermentation conditions, including over fifty genes with no previously known cellular function. This study provides a framework for understanding how yeast are adapted to fermentation and suggests possible means to improve the ability of commercial yeast strains to withstand the fermentation process. My NSERC Discovery Grant proposes to understand the mechanistic details of how autophagy is induced during fermentation and to provide a function for uncharacterized genes that have altered fitness during fermentation. Future implications of this proposal include developing stress resistant wine yeast strains with improved fermentation capability. Understanding stress resistance pathways in yeast creates potential to increase stress resistance in wine yeast, improve industrial performance and reduce the cost to Canadian wineries of incomplete (sluggish or stuck) fermentations.