The yeast TUM1 affects production of hydrogen sulfide from cysteine treatment during fermentation

The undesirable rotten-egg odour of hydrogen sulfide (H₂S) produced by yeast shortly after yeast inoculation of grape musts might be an important source of desirable varietal thiols, which contribute to tropical aromas in varieties such as Sauvign-on Blanc. In this study, we observed that Saccharomyces cerevisiae strains produce an early burst of H₂S from cysteine. Both Δmet2 and Δmet17 strains produce a larger burst, likely because they are unable to utilise the H₂S in the sulfate assimilation pathway. For the first time, we show that TUM1 is partly responsible for the early production of H₂S from cysteine. Overex-pressing TUM1 elevated production of H₂S, whilst its deletion yields only half of the H₂S. We further confirmed that yeast convert cysteine to H₂S by analysing growth of mutants lacking components of the transsulfuration pathway. High concent-rations of cysteine overcame this growth block, but required TUM1 Collectively, the data indicate that S. cerevisiae does not convert cysteine to sulfate or sulfite, but rather to sulfide via a novel pathway that requires the action of Tum1p. The findi-ngs of this study may allow the improvement of commercial yeasts through the manipulation of sulfur metabolism that are better suited towards production of fruit-driven styles.