Impact of Commercial Strain Use on Saccharomyces cerevisiae Population Structure and Dynamics in Pinot Noir Vineyards and Spontaneous Fermentations of a Canadian Winery

Wine is produced by one of two methods: inoculated fermentation, where a commercially-produced, single Saccharomyces cerevisiae ( S . cerevisiae ) yeast strain is used; or the traditional spontaneous fermentation, where yeast present on grape and winery surfaces carry out the fermentative process. Spontaneous fermentations are characterized by a diverse succession of yeast, ending with one or multiple strains of S . cerevisiae dominating the fermentation. In wineries using both fermentation methods, commercial strains may dominate spontaneous fermentations. We elucidate the impact of the winery environment and commercial strain use on S . cerevisiae population structure in spontaneous fermentations over two vintages by comparing S . cerevisiae populations in aseptically fermented grapes from a Canadian Pinot Noir vineyard to S . cerevisiae populations in winery-conducted fermentations of grapes from the same vineyard. We also characterize the vineyard-associated S . cerevisiae populations in two other geographically separate Pinot Noir vineyards farmed by the same winery. Winery fermentations were not dominated by commercial strains, but by a diverse number of strains with genotypes similar to commercial strains, suggesting that a population of S . cerevisiae derived from commercial strains is resident in the winery. Commercial and commercial-related yeast were also identified in the three vineyards examined, although at a lower frequency. There is low genetic differentiation and S . cerevisiae population structure between vineyards and between the vineyard and winery that persisted over both vintages, indicating commercial yeast are a driver of S . cerevisiae population structure. We also have evidence of distinct and persistent populations of winery and vineyard-associated S . cerevisiae populations unrelated to commercial strains. This study is the first to characterize S . cerevisiae populations in Canadian vineyards.