High quality and regional wines are characterized by the use of indigenous species of yeasts in co-fermentation with commercial strains, providing unique and robust flavors and aromas. Cultivation of indigenous species of yeasts of the grape berry may prove difficult with the diverse conditions required for growth, and the prevalence of commercial yeast species in the vineyard. Assessing yeast diversity on grapes in the absence of a commercial winery environment may prove useful in isolating indigenous yeasts. We hypothesized that yeasts isolated from greenhouse grapes would comprise of species not commonly associated with the vineyard environment, and would originate from outside the genus Saccharomyces. To test this hypothesis, 20 yeast isolates were collected from greenhouse and vineyard grapes. Qualitative growth response assays and rDNA genotyping were used to compare isolates at a phenotypic and genetic level, respectively. Among yeast isolates, vineyard isolates displayed more diversity at both a phenotypic and molecular level than the greenhouse isolates. In the vineyard, ethanol tolerant isolates belonged to the genus Metschnikowia, while the remaining belonged to the genus Hanseniaspora with few exceptions. The dominant greenhouse isolates were identified as the less ethanol tolerant species Debaromyces hanseneii. Through phylogenetic analysis, the Metschnikowia species isolated from the vineyard was found to be highly diverged from the commercial Saccharomyces cerevisiae strain EC1118. The species Hanseniaspora uvarum, D. hanseneii and S. cerevisiae EC1118 were most similar at the genetic level. Overall, we observed less yeast diversity than expected. We speculate that a liquid enrichment step may have selected for highly competitive species, and recommend exploring non-culture based methods to identify more species and to characterize diversity.
Yeasts from greenhouse grapes show less phenotypic and genetic diversity than yeasts from vineyard grapes when isolated from grape crush cultured in liquid media
Fall 2015 / Winter 2016