Effect of nitrogen status on competitive abilities between indigenous and commercial wine strains in alcoholic...

Nitrogen is the most limiting nutrient for yeast in alcoholic fermentation, but its roles in strain competitiveness during co-fermentation remains poorly explored. This study aimed to investigate the effects of nitrogen concentration and composition on the competitive fitness of indigenous and commercial S. cerevisiae strains in mixed fermentation from phenotypic to molecular levels. The indigenous strain G23 and the commercial strain RX60 were dominant under high‑nitrogen (HN) and low-nitrogen (LN) conditions, respectively, and single ammonium addition restored the competitiveness of G23 achieved in HN condition. Transcriptomic analysis indicated that the dominant strains at specific conditions exhibited overexpression of nitrogen permease genes (e.g., GAP1, DIP5, MEP1, MEP2, and MEP3) regulated by nitrogen catabolite repression (NCR), accompanied by activation of the positive transcriptional factor GAT1 and repression of the negative factor DAL80. Comparative genomics identified non-synonymous mutations in TOR1 between the two strains, and their differential TORC1 signaling activity (the main NCR regulator) was further verified by rapamycin tolerance assays. These findings suggested that the NCR-regulated nitrogen uptake capacity was a key determinant of the competition fitness between indigenous and commercial strains. This study sheds light on the critical function of nitrogen status on wine S. cerevisiae strain competitiveness in alcoholic fermentation, providing a new perspective for the rational selection and breeding of strains with superior colonization ability.