Brettanomyces bruxellensis SSU1 Haplotypes Confer Different Levels of Sulfite Tolerance When Expressed in a Saccharomyces cerevisiae SSU1 Null Mutant

Abstract

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 SO 2 , with relatively high concentrations of this antimicrobial needed for their control. Although SO 2 tolerance has been studied in several organisms and particularly in S. cerevisiae , little is known about the mechanisms that confer SO 2 tolerance in B. bruxellensis . Here, we confirmed the functionality of the sulfite efflux pump encoded by BbSSU1 and determined the efficiencies of four different BbSSU1 haplotypes. Gene expression analysis showed greater expression of the haplotype conferring greater SO 2 tolerance. Our results suggest that a combination of BbSSU1 haplotype efficiency, copy number, and haplotype expression levels likely contributes to the diverse SO 2 tolerances observed for different B. bruxellensis strains.