Résumé
In the context of yeast improvement, UV mutagenesis has been broadly used as a tool to generatenew genetic diversity, with great success for numerous phenotypes, including winemaking properties. In this study, we generated a library of 502 UV mutants of a commercial wine strain with the objective of ethanol yield modulation. The phenotypic characterisation of this library in wine-like laboratory fermentation, revealed a clear bimodal distribution for metabolites production and especially for succinate production. A selection of mutants from the two subpopulations was studied in depth. We observed strong differences between the two groups for almost all primary metabolites (ethanol, glycerol, acetate, pyruvate, α-ketoglutarate, malate and citrate). The observed patterns indicated that both TCA branches are impacted and suggested a succession of pathways ofproduction of intermediate metabolites such as pyruvate, α-ketoglutarate and succinate. Genomic analysis revealed that all mutants belonging to the low producer group completely lacked the mitochondrial genome, implying an absence of the respiratory chain. Although yeast in fermentation largely use glycolysis followed by alcoholic fermentation to assure its supply in ATP and to maintain its intracellular redox balance, our results highlighted a high importance of the mitochondria in fermentation metabolism, deeply affecting the production of compounds of great relevance in winemaking. Presently, the main hypothesis is a perturbation of the redox balance due to a lower fumarase activity that jeopardised cofactors re-oxidation. This study sheds unexpected light on the role of the respiratory chain in fermentation and opens up new perspectives of exploitation ofmutants with modified central carbon metabolism.