Abstract
Yeast cell death can occur during wine alcoholic fermentation, leading to stuck fermentations, which are a major issue for winemakers. Cell death is generally considered to result from ethanol stress that negatively affects membrane integrity. However, it has been recently found that yeast cell death is also related to nitrogen metabolism. Indeed, nitrogen starvation is one of the most frequently encountered starvations in oenological conditions, and yeast is able to cope with such deficiencies. However, cell death can also result from the inability of yeast to implement an appropriate stress response under some conditions of nutrient limitations which the yeast is unlikely to encounter in the wild. More specifically, a set of micronutrients (oleic acid, ergosterol, pantothenic acid and nicotinic acid) which was linked to cell death when present in low, growth-restricting concentrations was identified. Upon examination of gene expression under conditions of imbalance between nitrogen and these nontraditional micronutrients, it appeared that, in addition to already identified mechanisms of gene regulation in relation to nitrogen metabolism, some genes had specific deficiency regulations. This can also explain some of the observed cell mortality. Our data include specific regulations of certain key genes of lipid metabolism, as well as others related to DNA stability under unusual deficiency conditions. Our work allows us to propose a model for the mechanisms involved in controlling yeast mortality under oenological fermentation conditions.