Cross-Tolerance to Sulfite (SO₃H⁻) and Selenite (SeO₃²⁻) in Saccharomyces cerevisiae Strains Carrying SSU1-Associated Chromosomal Rearrangements

Introduction: Exposure of Saccharomyces cerevisiae to sulfite (SO₃H⁻) in winemaking environments has driven the selection of tolerant strains, often carrying chromosomal rearrangements (CRs) that enhance the expression of a sulfite efflux pump encoded by the gene SSU1. Recent studies suggest that protein ssu1p may also contribute to selenite (SeO₃²⁻) tolerance.

Methods: We identified S. cerevisiae strains carrying SSU1-associated CR VIII-t-XVI and XV-t-XVI. Additional sulfite-tolerant strains were isolated following adaptive laboratory evolution (ALE) experiments. Strains were used to investigate the potential connection between tolerance to sulfite and selenite.

Results: Our results show that S. cerevisiae CR strains, which tolerate sulfite levels up to ∼150 mg/L, also grow in media supplemented with high concentrations of selenite (i.e., 1.5 mM), suggesting a shared underlying mechanism of tolerance. Isolated strains obtained after 100 generations of adaptive laboratory evolution (ALE) under sulfite pressure were able to grow in a YPD agar supplemented with either sulfite or selenite. Interestingly, these isolates failed to regrow under these selective conditions if previously grown in a YPD agar without selective pressure.

Conclusion: Our findings support the existence of a common mechanism of toxicity for sulfite and selenite and indicate that sulfite/selenite tolerance acquired through ALE may represent a transient adaptive trait.