Brettanomyces bruxellensis SSU1Haplotypes Confer Different Levels of Sulfite Tolerance When Expressed in aSaccharomyces cerevisiae SSU1Null Mutant

Brettanomyces bruxellensis is one of the most important wine spoilage microorganisms, with the use of sulfite being the major method to control spoilage. However, this species displays a wide intraspecies distribution in sulfite tolerance, with some strains capable of tolerating high concentrations of SO2 , with relatively high concentrations of this antimicrobial needed for their control. Although SO2 tolerance has been studied in several organisms and particularly inS. cerevisiae , little is known about the mechanisms that confer SO2 tolerance inB. bruxellensis . Here, we confirmed the functionality of the sulfite efflux pump encoded byBbSSU1 and determined the efficiencies of four differentBbSSU1 haplotypes. Gene expression analysis showed greater expression of the haplotype conferring greater SO2 tolerance. Our results suggest that a combination ofBbSSU1 haplotype efficiency, copy number, and haplotype expression levels likely contributes to the diverse SO2 tolerances observed for differentB. bruxellensis strains.