Differences in the management of intracellular redox state between wine yeast species dictate their fermentation performances and metabolite production.

The maintenance of the balance between oxidized and reduced redox cofactors is essential for the functioning of many cellular processes in all living organisms. During Saccharomyces cerevisiae fermentation, it is supported by metabolism and consequently, modulates the formation of a wide range of by-products. In this study, we investigated the question of variability between wine yeast species in their management of redox balance and its consequences on the fermentation performances and the formation of metabolites. To this aim, we quantified the changes in NAD() and NADP() concentrations and redox status throughout the fermentation of 6 wine yeast species. While the availability of NADP and NADPH remained balanced and stable throughout the process for all the strains, important differences between species were observed in the dynamics of NAD and NADH intracellular pools. A comparative analysis of these data with the fermentation capacity and metabolic profiles of the strains revealed that Saccharomyces cerevisiae, Torulaspora delbrueckii and Lachancea thermotolerans strains were able to reoxidize NADH to NAD throughout the fermentation, mainly by the formation of glycerol. These speciesexhibited good fermentation capacities. Conversely, Starmerella bacillaris and Metschnikowia pulcherrima species were unable to regenerate NAD as early as one third of sugars were consumed, explaining at least in part their poor growth and fermentation performances. The Kluyveromyces marxianus strain exhibited a specific behaviour, by maintaining similar levels of NAD and NADH throughout the process. This balance between oxidised and reduced redox cofactors ensured the consumption of a large part of sugars by this species, despite a low fermentation rate. In addition, the dynamics of redox cofactors affected the production of by-products by the various strains either directly or indirectly, through the formation of precursors. Major examples are the increased formation of glycerol by S. bacillaris and M. pulcherrima strains, as a ...