Biocontrol of Brettanomyces/Dekkera bruxellensis in alcoholic fermentations using saccharomycin-overproducing Saccharomyces cerevisiae strains.

Microbial contamination of alcoholic fermentation processes (e.g. winemaking and fuel-ethanol production) is a serious problem for the industry since it may render the product unacceptable and/or reduce its productivity, leading to large economic losses. Brettanomyces/Dekkera bruxellensis is one of the most dangerous microbial contaminant of ethanol industrial fermentations. In the case of wine, this yeast species can produce phenolic compounds that confer off-flavours to the final product. In fuel-ethanol fermentations, D. bruxellensis is a persistent contaminant that affects ethanol yields and productivities. We recently found that Saccharomyces cerevisiae secretes a biocide, which we named saccharomycin, composed of antimicrobial peptides (AMPs) derived from the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Saccharomycin is active against several wine-related yeast species, namely D. bruxellensis. However, the levels of saccharomycin naturally secreted by S. cerevisiae during alcoholic fermentation are not sufficient to ensure the complete death of D. bruxellensis. Therefore, the aim of the present work was to construct genetically modified S. cerevisiae strains to overproduce these GAPDH-derived AMPs. The expression levels of the nucleotides sequences encoding the AMPs were evaluated in the modified S. cerevisiae strains by RT-qPCR, confirming the success of the recombinant approach. Furthermore, we confirmed by immunological tests that the modified S. cerevisiae strains secreted higher amounts of the AMPs by comparison with the non-modified strain, inducing total death of D. bruxellensis during alcoholic fermentations.