Search

Vineyards and wineries are ecological habitats that house a diverse community of yeast and bacteria. Grapes and cellars are two sources of S. cerevisiae strains involved in the winemaking process, but the relationship between both S. cerevisiae populations is still poorly understood. Indeed strains in vineyards samples are rarely the same as those isolated from vats. In order to better apprehend this issue, 1374 S. cerevisiae isolates were collected from 193 samples of Merlot grapes obtained across 5 Bordeaux regions and from 11 spontaneously fermenting must of 7 cellars. We obtained 402 different genotypes using 17 microsatellite markers. A first analysis of genotypes indicated that approximately ¼thof isolates presented more than 75% of similarity with commercial yeast starters, suggesting that they escaped from the cellar environment, but presented variations higher that could be detected from the analysis of their industrial batch production. The resulting S. cerevisiae populations of 302 grapes-associated and 225 cellar-associated unique profiles revealed a global low differentiation (Fst=0.036), but with differences from sites to sites. To limit potential geographic or sampling effects, a subset of 72 individuals were selected among the vineyard and cellar isolates, representing 5 cellars and the vines located in their immediate environment. Again a low differentiation was noticed (Fst= 0.03 +/- 0.001). The geneflow between vines and cellars was inferred, using a likelihood approach implemented in the software MIGRATE. Inferences showed that cellar and grape metapopulations present similar theoretical sizes and are connected by asymmetric geneflow: almost 4 times higher in the direction "grapes-to-cellar" than for "cellar-to-grapes" (number of migrants per generation 191 [166 -226] versus 55 [25 - 83], respectively). This reveals that vines and cellars are two compartments of the same ecosystem, which has deep ecological significance.

International audience; Hanseniaspora uvarum is one of the most abundant yeast species found on grapes and in grape must, at least before the onset of alcoholic fermentation (AF) which is usually performed by Saccharomyces species. The aim of this study was to characterize the genetic and phenotypic variability within the H. uvarum species. One hundred and fifteen strains isolated from winemaking environments in different geographical origins were analyzed using 11 microsatellite markers and a subset of 47 strains were analyzed by AFLP. H. uvarum isolates clustered mainly on the basis of their geographical localization as revealed by microsatellites. In addition, a strong clustering based on year of isolation was evidenced, indicating that the genetic diversity of H. uvarum isolates was related to both spatial and temporal variations. Conversely, clustering analysis based on AFLP data provided a different picture with groups showing no particular characteristics, but provided higher strain discrimination. This result indicated that AFLP approaches are inadequate to establish the genetic relationship between individuals, but allowed good strain discrimination. At the phenotypic level, several extracellular enzymatic activities of enological relevance (pectinase, chitinase, protease, β-glucosidase) were measured but showed low diversity. The impact of environmental factors of enological interest (temperature, anaerobia, and copper addition) on growth was also assessed and showed poor variation. Altogether, this work provided both new analytical tool (microsatellites) and new insights into the genetic and phenotypic diversity of H. uvarum, a yeast species that has previously been identified as a potential candidate for co-inoculation in grape must, but whose intraspecific variability had never been fully assessed.

Saccharomyces cerevisiae is the main actor of wine fermentation but still little is known about the factors impacting its distribution in the vineyards. Bordeaux region, by its history and its appellations, is one of the regions of interest to study S. cerevisiae diversity. A total of 2422 isolates of S.cerevisiae sampled from grapes and spontaneous fermentation tanks during two consecutive years were analyzed by 15 to 17 microsatellite markers. A very high genetic diversity is demonstrated, greater in conventional farming system than in organic one. The type of farming system weakly influences the population structure of S.cerevisiae in the vineyard. The appellation and the wine estate significantly impact the population structure, without appearance of diversity gradients, but our analyses reveal important connections from the Pessac-Léognan to other Bordeaux appellations, especially to the Medoc. Bidirectional strong flows are highlight between the vineyard and the cellar compartments as illustrated by the presence of 25% of commercial related strains in the vineyard, due to the unexpected return of strains through cellar to the vineyard, while a flow of similar magnitude is observed between the vineyard and the cellar. The presence of common ancestral populations in old (over 20 years) and recent samples showed population stability over the long-term at an appellation scale. A temporal succession of cellar populations was highlighted that could be link with the implementation of the Pied de Cuve method through successive inoculations.; Saccharomyces cerevisiae est l’acteur principal de la fermentation du moût de raisin, mais l’influence de facteurs sur sa distribution dans les vignobles est peu connue. La région bordelaise, par son histoire et ses appellations, est une région d’intérêt pour étudier la diversité de S.cerevisiae. Au total, 2422 isolats de S.cerevisiae provenant de prélèvements de raisins et de cuves en fermentation spontanées sur deux années consécutives ont été analysés par 15 à 17 marqueurs microsatellites. Une très grande diversité génétique est mise en évidence, supérieure en mode de conduite conventionnel par rapport au mode biologique. Le mode de conduite influence faiblement la structure de la population de S.cerevisiae au vignoble. L’appellation et le domaine impactent significativement la structure de population, sans que des gradients de diversité n‘apparaissent, mais nos analyses révèlent des connections importantes dans le sens Pessac-Léognan vers les autres appellations du Bordelais, en particulier le Médoc. Des flux importants bidirectionnels sont mis en évidence entre les compartiments vigne et chai, illustrés par la présence de 25% de souches apparentées à des levures commerciales au vignoble, retour des souches du chai au vignoble jusqu’alors sous-estimé, alors qu’un flux d’importance similaire est observé entre le vignoble et le chai. La présence de populations ancestrales communes dans des prélèvements anciens (plus de 20 ans) et récents révèle la stabilité des populations sur le long terme à l’échelle d’une appellation. Une succession temporelle des populations du chai pourrait être favorisée par la mise en œuvre de pied de cuve avec repiquages successifs.