A set of nutrient limitations trigger yeast cell death in a nitrogen-dependent manner during wine alcoholic fermentation
Résumé
Yeast cell death can occur during wine alcoholic fermentation. It is generally considered to
result from ethanol stress that impacts membrane integrity. This cell death mainly occurs
when grape musts processing reduces lipid availability, resulting in weaker membrane resistance
to ethanol. However the mechanisms underlying cell death in these conditions remain
unclear. We examined cell death occurrence considering yeast cells ability to elicit an appropriate
response to a given nutrient limitation and thus survive starvation. We show here that
a set of micronutrients (oleic acid, ergosterol, pantothenic acid and nicotinic acid) in low,
growth-restricting concentrations trigger cell death in alcoholic fermentation when nitrogen
level is high. We provide evidence that nitrogen signaling is involved in cell death and that
either SCH9 deletion or Tor inhibition prevent cell death in several types of micronutrient limitation.
Under such limitations, yeast cells fail to acquire any stress resistance and are
unable to store glycogen. Unexpectedly, transcriptome analyses did not reveal any major
changes in stress genes expression, suggesting that post-transcriptional events critical for
stress response were not triggered by micronutrient starvation. Our data point to the fact
that yeast cell death results from yeast inability to trigger an appropriate stress response
under some conditions of nutrient limitations most likely not encountered by yeast in the
wild. Our conclusions provide a novel frame for considering both cell death and the management
of nutrients during alcoholic fermentation.
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