Study of the genetic and physiological basis of nitrogen requirement of Saccharomyces cerevisiae yeasts in alcoholic fermentation.

Summary Oenological strains show a significant diversity in their nitrogen requirements, which translates into differences in fermentative capacity. At present, the mechanisms involved in the variability of fermentation profiles, following a nitrogen depletion in the environment, are not known. The identification of these mechanisms would be an asset in the understanding of the phenomena leading to problematic fermentations and in fermentation restarts. In order to identify these mechanisms, we coupled a classical physiological and genomic approach with a genetic approach involving the search for QTLs based on the fermentative efficiency under nitrogen deficiency conditions. We characterized this difference in nitrogen requirement between strains as a variability in the ability to perceive nitrogen deficiency and to develop a quiescence program that reduces energy flow and increases a stress state. These energy shifts then translate into differences in fermentative capacity. The QTL approach allowed us to detect 23 regions of the genome potentially involved in the maintenance of fermentative capacity. After analysis, we identified 4 genes whose allelic variations are responsible for phenotypic variations between strains. The use of these genes could allow the design of genetic markers, exploited for the selection of strains with good fermentative capacities. Data from this QTL approach suggest a close correlation between differences in stress response by strains and the involvement of nitrogen perception and signaling mechanisms. Finally, our work offers a new hypothesis, pointing to the TOR pathway as the mechanism responsible for the variation in fermentative capacities between strains.