Grape berry bacterial microbiota: Impact of the ripening process and the farming system

Wine grapes are a primary source of microbial communities that play a prominent role in the quality of grapes prior to harvesting, as well as in the winemaking process. This study investigated the dynamics and diversity of the epiphytic bacteria on the grape berry surface during maturation. The quantitative and qualitative effects of conventional and organic farming systems on this microbial community were investigated, using both cultivation-dependent and independent approaches. Analyses of grape berry bacterial microbiota revealed changes in the size and structure of the population during the berry ripening process, with levels rising gradually and reaching their highest value when the berries were over ripe. As the season progressed to maturity, Gram-negative bacterial communities (mostly Pseudomonas spp.) declined whereas Gram-positive communities (mostly Micrococcus spp.) increased. The 16S rRNA gene sequences of cultured isolates were analysed and over 44 species were identified from 21 genera in the Proteobacteria, Actinobacteria, and Firmicutes phyla. Copper concentrations originating from phytosanitary treatments varied according to the vineyard and farming system. A negative correlation between copper concentrations and cell densities provided clear evidence that copper inhibited bacterial communities. The bacterial community structure was analysed by targeting the 16S rRNA genes, using PCR-DGGE on cultivable populations and T-RFLP on whole communities in cell suspension. The results suggest that the farming system has a clear impact on the bacterial community structure.