Abstract: To elucidate the regulatory effects of Zaosha fermentation on the pit mud microecosystem in Jiangxiangxing Baijiu production, this study integrated high-throughput sequencing and untargeted metabolomics to systematically investigate the microbial diversity, community assembly mechanisms and interaction networks, as well as their relationships with metabolites and physicochemical factors in pit mud before and after fermentation. The results showed that Zaosha fermentation significantly reduced bacterial abundance while increasing bacterial diversity, whereas fungal diversity remained relatively stable. Community structure analysis identified Trichoderma, Pichia, Wickerhamomyces, Penicillium, and Sinomonas as key taxa driving microbial succession during the fermentation process. Null model-based community assembly analysis showed that Zaosha fermentation enhanced the contribution of heterogeneous selection to the assembly of bacterial and fungal communities, shifting microbial community assembly from stochastic to deterministic processes; this transition was closely associated with enhanced environmental filtering. Co-occurrence network analysis indicated that Zaosha fermentation promoted the transition of microbial interactions from dispersed to more compact and highly modular structures, with the bacterial network exhibiting more stable metabolic division of labor. Metabolomic profiling demonstrated that Zaosha fermentation markedly reshaped the metabolite composition of pit mud, with lipids and lipid-like molecules being the predominant differential metabolites. Polyunsaturated fatty acids, eicosanoids, phospholipids, and carbohydrates were significantly enriched after fermentation. Microbe-metabolite correlation analysis suggested that dominant genera such as Lodderomyces, Trichosporon, Trichoderma, and Acinetobacter may cooperatively regulate fatty acid, nucleotide, and cell wall-related metabolism, contributing to the formation of flavor precursor compounds in Baijiu. Collectively, these findings demonstrate that Zaosha fermentation drives microbial community assembly and interaction network reorganization in pit mud, and shapes microbial metabolic function through environmental regulation. This provides new insights into the microecological mechanisms underlying the quality formation of Jiangxiangxing Baijiu.

Key words: Jiangxiangxing Baijiu; pit mud; microbial community assembly; co-occurrence network; metabolomics