Genetic causes of SO₂ consumption in Saccharomyces cerevisiae

Abstract

SO2 is used during winemaking for its anti-oxidative and anti-microbial properties. A high SO2 concentration in the wine has negative impacts by hiding wine aromas and delaying malolactic fermentation. SO2 concentration is also a source of health concerns and is therefore legally regulated. During the alcoholic fermentation SO2 can be produced or consumed by the yeast Saccharomyces cerevisiae with a high variability depending on the strain that accomplish the fermentation. The selection of industrial strains leaving less SO2 at the end of fermentation is therefore of great interest. 

In this study we implemented a QTL (Quantitative Trait Loci) mapping program to identify genetic factors that impact SO2 production by yeast during fermentation. This approach requires the study of a large progeny in segregation that must be characterized genetically and phenotypically. The establishment of a statistical link between genotype and phenotype allows the localization of QTLs that have an impact on the characters. 

Small-scale fermentations in 10 ml screw cap vessels coupled with robotized enzymatic allowed us to measure SO2 profile of several hundred individuals from two progenies. These two progenies were also genotyped by whole genome sequencing providing saturated genetic maps of thousands of markers. This experimental design led us to the identification of nine QTLs controlling SO2. Four of them present in MCH1, STR2 and SSU1 genes were molecularly validated. These alleles also show a pleiotropic effect with link between the production of SO2 and acetic acid. In the future, these new alleles can be used in cross breeding programs for the improvement of industrial strains.