Abstract Description

Saccharomyces cerevisiae is the main yeast starter culture used to drive alcoholic fermentation in the wine industry, because of its strong and reliable fermentation performances. Nevertheless, unconventional non-Saccharomyces yeasts have progressively gained interest over the past few decades to complement S. cerevisiae's properties and reduce chemical inputs. Furthermore, these yeasts are now being considered no longer only for their ability to produce aromas but also to address new challenges such as climate change. Indeed, global warming alters the chemical composition of grape berries. For instance, sugar concentration increases, which in turn leads to higher alcohol content in wine together with the accumulation of undesired metabolites such as acetic acid. Amongst non-Saccharomyces yeasts, Lachancea thermotolerans stands out for its ability to generate lower acetic acid yields under winemaking conditions, but the biochemical reasons behind this specific trait remain unknown. Acetic acid production is closely linked to the metabolism of coenzyme A (CoA), an essential cofactor produced from pantothenic acid (vitamin B5), which is naturally found in grape juice. In this context, this study aimed to investigate pantothenic acid (PA) requirements in L. thermotolerans. The ability of 20 Lachancea spp. strains to grow in synthetic grape must without PA was evaluated. The data revealed three main behaviours: no impact on the growth parameters, longer lag phase and lower biomass production but similar growth rate, or slower growth rate and lower biomass production. Six strains representative of the different behaviours were selected, and their ability to adapt to the lack of PA over several generations was assessed. Interestingly, despite the differences observed between strains in their response to PA deficiency, results suggest that CoA recycling is not the only mechanism used by all the strains to adapt to the stress generated by the lack of PA. Furthermore, exogenous PA deficiency induced various cellular and metabolic alterations. Indeed, Nile Red staining showed a reduced intracellular neutral lipid concentration. Moreover, microscopic observations coupled with flow cytometry revealed that PA deficiency also led to cell aggregation and greater variability in cell size and granularity in some strains, which suggests a remodelling of the cell membrane composition in the absence of PA. Taken together, the data show a great diversity between L. thermotolerans strains in their response to PA deficiency, which suggests different metabolic adaptations. The knowledge gained through this study contributes to our broader understanding of L. thermotolerans' nutrient requirements and metabolism. Ultimately it will help optimise their utilisation in winemaking.