The impact of CUP1 gene copy-number and XVI-VIII/XV-XVI translocations on copper and sulfite tolerance in vineyard Saccharomyces cerevisiae strain populations.

In wine production, sulfites are widely used as antimicrobials and antioxidants, whereas copper is associated with fungicides and wine fining treatments. Therefore, wine yeasts are constantly exposed to these agents. Copper tolerance is related to the copy number of the CUP1 gene, encoding for a metallothionein involved in copper detoxification. In wine yeasts, sulfite resistance mainly depends on the presence of the translocation t(XVI;VIII) in the promoter region of the SSU1 gene. This gene encodes for a plasma membrane sulfite pump involved in sulfite metabolism and detoxification. Recently, a new translocation, t(XVI;VIII), was identified. In this work, 253 Saccharomyces cerevisiae strains, representing three vineyard populations from two different continents, were analyzed, along with 20 industrial starters. Copper and sulfites tolerance as well as distribution of CUP1 gene copy-number, t(XVI;VIII)and t(XVI;XV) of SSU1 gene were studied to evaluate the impact of these genomic variations on population phenotypes. The CUP1 gene copy-number was found to be highly variable, ranging from zero to 79 per strain. Moreover it differently impacted the copper tolerance in the populations of the two continents. The diffusion of t(XVI;VIII) and, for the first time, t(XVI;XV) was determined in the three vineyard populations. The correlation between the presence of the translocation and strain sulfite tolerance levels was significant only for the t(XVI;VIII).

Genetic variability and physiological traits of Saccharomyces cerevisiae strains isolated from "Vale dos Vinhedos" vineyards reflect agricultural practices and history of this Brazilian wet subtropical area.

Vale dos Vinhedos appellation of origin has a very recent history as industrial wine making region. In this study we investigated the genetic and phenotypic variability of Saccharomyces cerevisiae strains isolated from South-Brazilian vineyards in order to evaluate strain fermentation aptitude and copper and sulphites tolerance. Merlot grape bunches were collected from three vineyards and yeast isolation was performed after single bunch fermentation. High genotypic variability was found and most of the genotypes revealed to be vine-specific. No industrial strain dissemination was present in the sampled vineyards, although it has been wildly reported in traditional winemaking countries. From the phenotypic traits analysis these Brazilian native strains showed good fermentation performances, good tolerance to sulphites and, in particular, a high copper tolerance level. Copper is the most important metal in the formulation of fungicides against downy mildew (Plasmopara viticola), one of the most harmful disease of the vines, and other fungal pests. The high tolerance to copper suggests an environmental adaptation to the strong use of copper-based fungicides, requested by the wet subtropical climate.

Corrigendum: Biocontrol Ability and Action Mechanism of Starmerella bacillaris (Synonym Candida zemplinina) Isolated from Wine Musts against Gray Mold Disease Agent Botrytis cinerea on Grape and Their Effects on Alcoholic Fermentation.

[This corrects the article on p. 1249 in vol. 7, PMID: 27574517.].

Biocontrol Ability and Action Mechanism of Starmerella bacillaris (Synonym Candida zemplinina) Isolated from Wine Musts against Gray Mold Disease Agent Botrytis cinerea on Grape and Their Effects on Alcoholic Fermentation.

Gray mold is one of the most important diseases of grapevine in temperate climates. This plant pathogen affects plant growth and reduces wine quality. The use of yeasts as biocontrol agents to apply in the vineyard have been investigated in recent years as an alternative to agrochemicals. In this work, fermenting musts obtained from overripe grape berries, therefore more susceptible to infection by fungal pathogens such as Botrytis cinerea, were considered for the selection of yeasts carrying antifungal activity. Thirty-six isolates were identified as Starmerella bacillaris, a species recently proven to be of enological interest. Among them 14 different strains were studied and antifungal activity against B. cinerea was demonstrated, for the first time, to be present in S. bacillaris species. The production of volatile organic compounds (VOCs), tested in vitro, was found to be the main responsible of S. bacillaris antifungal effects. All the strains were able to reduce B. cinerea decay on wounded grape berries artificially inoculated with gray mold. The colonization level of wound was very high reaching, after 5 days, a concentration of 10(6) cells per ml of grape juice obtained after berry crushing. At this cell concentration S. bacillaris strains were used to ferment synthetic and natural musts. The sequential yeast inoculation, performed by adding S. cerevisiae 48 h after S. bacillaris, was needed to complete sugar consumption and determined a significant increase in glicerol content and a reduction of ethanol and acetic acid concentrations. The high wound colonization ability, found in this work, together with the propensity to colonize grape berry and the interesting enological traits possessed by the selected S. bacillaris strains allow the use of this yeast as biocontrol agent on vine and grape berries with possible positive effects on must fermentation, although the presence of S. cerevisiae is needed to complete the fermentation process. This work introduces new possibilities in wine yeast selection programs in order to identify innovative wine yeasts that are simultaneously antifungal agents in vineyards and alternative wine starters for grape must fermentation and open new perspective to a more integrated strategy for increasing wine quality.