Multi-omics insights into sulfur metabolism and methylthio alcohols formation during industrial radish paocai fermentation.

Sichuan paocai is a traditional Chinese fermented vegetable whose characteristic aroma is strongly influenced by volatile sulfur-containing compounds (VSCs). Among them, 3-(methylthio)-1-propanol and 2-(methylthio)ethanol are key odor-active components, yet their biosynthetic mechanisms and microbial drivers in paocai remain poorly understood. In this study, an integrated metatranscriptomic, metaproteomic, and metabolomic approach was employed to systematically elucidate the formation pathways of these two methylthio alcohols during industrial radish paocai fermentation. Dynamic changes in microbial community structure, functional gene and protein expression, and pathway-related metabolites were comprehensively analyzed across fermentation stages. The results revealed a clear microbial succession from yeast-dominated communities in early fermentation to lactic acid bacteria dominance in later stages, accompanied by pronounced shifts in sulfur metabolism activity. Reconstruction of methylthio alcohols biosynthetic pathways demonstrated that methionine metabolism, sulfur-containing amino acid conversion, and methionine salvage collectively supply key precursors and intermediates. Multiple enzymes involved in sulfur assimilation, transamination, decarboxylation, and reduction were actively expressed, particularly during mid-to-late fermentation. Correlation analyses further identified Debaryomyces hansenii, Zygosaccharomyces rouxii, and Lactobacillus ginsenosidimutans as core functional microorganisms, acting in a coordinated manner to regulate precursor supply and terminal conversion steps. Overall, this study provides a mechanistic framework linking active microorganisms, expressed enzymes, and metabolite dynamics in methylthio alcohols biosynthesis. The findings advance understanding of sulfur metabolism regulation in open, plant-based fermentations and offer a scientific basis for targeted modulation of sulfur-derived aroma compounds in industrial paocai production.