LARGE-SCALE PHENOTYPIC SCREENING OF THE SPOILAGE YEAST BRETTANOMYCES BRUXELLENSIS: UNTANGLING PATTERNS OF ADAPTATION AND SELECTION, AND CONSEQUENCES FOR INNOVATIVE WINE TREATMENTS

Abstract

Brettanomyces bruxellensis is considered as the main spoilage yeast in oenology. Its presence in red wine leads to off-flavour due to the production of volatile phenols such as 4-vinylphenol, 4-vinylguaiacol, 4-ethylphenol and 4-ethylguaiacol, whose aromatic notes are unpleasant (e.g. animal, leather, horse or pharmaceutical). Beside wine, B. bruxellensis is commonly isolated from beer, kombucha and bioethanol production, where its role can be described as negative or positive. Recent genomic studies unveiled the existence of various populations. These genetic groups differ from each other by their ploidy level (diploid or triploid), their hybridization status (auto or- allo-triploid) and their ecological fermentation niches (wine, beer, tequila/bioethanol, etc.). While the genomic landscape of B. bruxellensis is nowadays clearer, its phenotypic diversity is still insufficiently assessed in the light of its genetic diversity. In this work, on one hand, we designed an experiment where 151 B. bruxellensis strains representative of the genetic diversity of the species were phenotypically characterized in five natural beverages (grape must, wine, wort, beer, kombucha wort). Various phenotypic traits were monitored: parameters of growth and fermentation ability, metabolites of technological interest… Signatures of local adaptation were investigated and showed that at least one allotriploid population of B. bruxellensis is specifically adapted to wine environment. Moreover, such large screening allowed the identification of ancestral traits like maltose and maltotriose consumption or nitrate metabolization that were randomly lost in specific populations, an evolutionary phenomenon called relaxed selection. On a second hand, two innovative control methods, continuous UV-C light and pulsed light, were tested on a large collection of B. bruxellensis (>100 strains) and other wine yeast species (14 species). These two stabilization treatments were deemed as particularly efficient on wine yeast spoilers (B. bruxellensis including) using i- a drop-platted system to screen various strains and conditions, and ii- lab-made reactors to stabilize several litters of red wines. Altogether, our results contribute to a deeper understanding of the wine spoiler B. bruxellensis both at the fundamental and applied levels.