Wine Production
The winemaking process makes use of a lot of different microbes. The yeast, Saccharomyces cerevisiae, is involved in fermenting sugars into alcohol while lactic acid bacteria including Oenococcus oeni, are involved in malo-lactic fermentation which reduces the acidity of wine.
Another yeast, called Brettanomyces bruxellensis, can also appear during winemaking, but is not welcome. It releases volatile compounds, called phenols, that cause an unpleasant change in the aroma of the wine. This is called the ‘Brett character’ and people describe it as the smell of ‘wet dog‘, horse sweat or leather – not very nice.
Wine can be stored in wood or stainless-steel barrels, and B. bruxellensis can grow as biofilms on both these surfaces. Being able to grow as a biofilm helps it survive in what would otherwise be a very hostile and acidic environment.
Great advances in genome sequencing have enabled the study of more than 1500 isolates of the spoilage yeast, Brettanomyces bruxellensis, from different environments (wine, beer, tequila, kombucha, bioethanol and cider) and divided them into six genetic groups depending on their ploidy and the substrate from which they were isolated.
An article published in 2019 (Cibrario et al., 2019) showed there was high genetic diversity amongst B. bruxellensis isolates: 58 and 42% of triploid and diploid individuals, respectively, were distributed in five main genetic groups. Their distribution amongst these groups was dependent on the country and/or wine-producing region of origin.
In the same article the authors also observed diversity in the biological attributes (phenotype) of the isolates. For example, two different groups of triploid isolates (associated with wine) were either tolerant or resistant to sulphur dioxide, the most common preservative used in winemaking.
In combination, the ability of B. bruxellensis to survive in the wine environment by forming biofilms on surfaces, and its resistance to sulfur dioxide, make it a very challenging species to control.
Image: Scanning electron micrographs of 7-day-old microcolonies of two isolates of Brettanomyces bruxellensis grown as bioflms on stainless steel chips in wine. Genetic distribution of Brettanomyces bruxellensis wine isolates from different regions and countries.
Further reading on biofilms and wine
Cibrario, A., Avramova, M., Dimopoulou, M., Magani, M., Miot-Sertier, C., Mas, A., Portillo, M.C., Ballestra, P., Albertin, W., Masneuf-Pomarede, I., Dols-Lafargue, M. (2019) ‘Brettanomyces bruxellensis wine isolates show high geographical dispersal and long persistence in cellars’, PLOS ONE, vol. 14(2), e0222749, https://doi.org/10.1371/journal.pone.0222749