Effects of nitrogen catabolite repression and di-ammonium phosphate addition during wine fermentation by a commercial strain of S. cerevisiae.

Two deletion mutants expected to be defective in nitrogen catabolite repression (NCR) were constructed in a commercial wine yeast background M2: a ure2 mutant and a dal80 gzf3 double mutant. Wild-type and both mutant strains were fermented in Sauvignon Blanc grape juice with and without addition of di-ammonium phosphate (DAP). The dal80 gzf3 double mutant exhibited a long fermentative lag phase, which was offset by DAP addition (corresponding to 300 mg/L of N). Neither the NCR mutations nor DAP addition affected the content of volatile thiols in the final wine. Microarray analyses of transcripts in the wild-type and dal80 gzf3 double-mutant strains were performed after 2% and 70% sugars were fermented. Of 80 genes previously identified as NCR-regulated, only 13 were upregulated during fermentation of the dal80 gzf3 double-mutant strain in grape juice. Following DAP addition, 34 of the known NCR genes were downregulated, including 17 that were downregulated even in the NCR mutant strain. The results demonstrate an unexpected complexity of the NCR response that may reflect differences between strains of yeast or differences in gene regulation during alcoholic fermentation compared with standard aerobic growth.