Phenotypic variations of primary metabolites yield during alcoholic fermentation in the Saccharomyces cerevisiae species

Abstract

Saccharomyces cerevisiae, as the workhorse of alcoholic fermentation, is a major actor of winemaking. In this context, this yeast species uses alcoholic fermentation to convert sugars from the grape must into ethanol and CO2 with an outstanding efficiency: it reaches on average 92% of the maximum theoretical yield of conversion. Moreover, S. cerevisiae is also known for its great genetic diversity and plasticity that is directly related to its living environment, natural or technological and therefore to domestication. This leads to a great phenotypic diversity of metabolites production. However, the metabolic diversity is variable and depends on the pathway considered. Primary metabolites produced during fermentation stand for a great importance in wine where they significantly impact wine characteristics. Ethanol indeed does, but others too, which are found in lower concentrations: glycerol, succinate, acetate, pyruvate, alpha-ketoglutarate… Their production, which can be characterised by a yield according to the amount of sugars consumed, is known to differ from one strain to another. In the aim to improve wine quality, the selection, development and use of strains with dedicated metabolites production without genetic modifications have to rely on the natural diversity that already exists. Here we detail a screening that aims to assess this diversity of primary metabolites production in a set of 51 S. cerevisiae strains from various genetic backgrounds (wine, flor, rum, West African, sake…). To approach winemaking conditions, we used a synthetic grape must as fermentation medium and measured by HPLC six main metabolites. Results obtained pointed out great yield differences between strains and that variability is dependent on the metabolite considered. Ethanol appears as the one with the smallest variation among our set of strains, despite it’s by far the most produced. However, as long as a small variability is measurable there is room for improvement. A clear negative correlation between ethanol and glycerol yields has been observed, confirming glycerol synthesis as a good lever to impact ethanol yield. Some genetic groups have been identified as linked to high production of specific metabolites, like succinate for rum strains or alpha-ketoglutarate for wine strains. This study thus helps to define the phenotypic diversity of S. cerevisiae in a wine-like context and supports the use of ways of development of new strains exploiting natural diversity. Finally, it provides a detailed data set usable to study diversity of primary metabolites production, including common commercial wine strains.