Abstract
The yeast species Brettanomyces bruxellensis is associated with important economic losses due to red wine spoilage. The most common method to prevent and/or control B. bruxellensis spoilage in winemaking is the addition of sulfur dioxide into must and wine. However, recently, it was reported that some B. bruxellensis strains could be tolerant to commonly used doses of SO2. In this work, B. bruxellensis response to SO2 was assessed in order to explore the relationship between SO2 tolerance and genotype. We selected 145 isolates representative of the genetic diversity of the species, and from different fermentation niches (roughly 70% from grape wine fermentation environment, and 30% from beer, ethanol, tequila, kombucha, etc.). These isolates were grown in media harboring increasing sulfite concentrations, from 0 to 0.6 mg.L-1 of molecular SO2. Three behaviors were defined: sensitive strains showed longer lag phase and slower growth rate and/or lower maximum population size in presence of increasing concentrations of SO2. Tolerant strains displayed increased lag phase, but maximal growth rate and maximal population size remained unchanged. Finally, resistant strains showed no growth variation whatever the SO2 concentrations. 36% (52/145) of B. bruxellensis isolates were resistant or tolerant to sulfite, and up to 43% (46/107) when considering only wine isolates. Moreover, most of the resistant/tolerant strains belonged to two specific genetic groups, allowing the use of microsatellite genotyping to predict the risk of sulfur dioxide resistance/tolerance with high reliability (>90%). Such molecular diagnosis could help the winemakers to adjust antimicrobial techniques and efficient spoilage prevention with minimal intervention.
Highlights
Winemakers manage the transformation of must into wine through various processes, aiming to obtain high quality product according to their wishes and the expectations of their customers
The most common method to prevent and/or control B. bruxellensis spoilage remains the addition of sulfur dioxide into must and wine, with regular adjustments if needed
Sulfur dioxide is usually used by winemakers as preventive or curative treatment for spoilage microorganisms including B. bruxellensis contamination
Summary
Winemakers manage the transformation of must into wine through various processes, aiming to obtain high quality product according to their wishes and the expectations of their customers. Over the last years, some B. bruxellensis strains were reported to be tolerant to commonly used doses of SO2, with a high variability amongst isolates (Barata et al, 2008; Curtin et al, 2012; Agnolucci et al, 2014) This variability makes the prediction of B. bruxellensis spoilage potential and the choice of adequate antimicrobial agent a challenge for winemakers. The aims of this study were (i) to extend the screening of SO2 sensitivity to 106 additional isolates and confirm/infirm the correlation between genetic clusters and SO2 sensitivity to a larger collection representative of the global B. bruxellensis population and (ii) to validate the applicability of a method allowing the prediction of B. bruxellensis SO2 sensitivity through genetic markers analysis
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