Sulfur Dioxide Treatment Alters Wine Microbial Diversity and Fermentation Progression in a Dose-Dependent Fashion

The use of sulfur dioxide (SO2) as an antimicrobial in winemaking is a well-established, common practice. Although much is known about the antimicrobial effects of SO2 at single concentrations, little is known about its effects on microbial growth dynamics across a range of concentrations or when used in conjunction with yeast inoculation. Using high-throughput marker-gene sequencing, we investigated the cumulative impacts of yeast inoculation and SO2 treatments across a broad concentration range (0 to 150 mg/L SO2) on the bacterial and fungal communities in wine fermentations. Our results indicated a dose-dependent effect of SO2, with lactic acid bacteria and Gluconobacter proliferating in fermentations with <25 mg/L SO2, but other bacteria and fungi were unaffected by the SO2 addition. Microbial profiles stabilized at concentrations >= 25 mg/L SO2, and fermentation performance decreased at higher concentrations (100 to 150 mg/L SO2). Yeast inoculation alone conferred a stabilizing effect, reducing the bacterial growth observed in unsulfited fermentations, but this effect was not additive with an increase in SO2 concentrations.