Differential Regulation of Microbial Community Succession by Bacillus velezensis and Its Impact on Flavor Compound Synthesis During Xiaoqu Baijiu Fermentation Stage

To address the demand for quality improvement in Xiaoqu Baijiu, this study evaluated bioaugmented fermentation using previously screened saccharification-promoting strains, Bacillus velezensis FUBL1 (B1) and FUBL3 (B3), to elucidate their impacts on physicochemical dynamics, microbial succession, and volatile flavor metabolism. High-throughput sequencing, Spearman correlation analysis, and flavor profiling were employed to track fermentation dynamics and cross-kingdom microbial interactions. The results demonstrated that bioaugmentation significantly enhanced sugar utilization efficiency. By the end of fermentation, total ester contents in fermented grains (jiupei) increased by 16.80% (B1) and 11.64% (B3) compared with the control. Upregulated long-chain fatty acid ethyl esters (e.g., ethyl laurate and ethyl palmitate) potentially contribute to enhancing floral/fruity aromatic qualities. From the perspective of microbial dynamics, Bacillus dominated the initial fermentation stage (up to 86.24%) and co-established a dominant niche with Pediococcus in mid-to-late stages. Exogenous inoculation accelerated the ecological dominance of Saccharomyces cerevisiae without competitive inhibition and increased the relative abundance of flavor-associated fungi like Candida. Spearman correlation analysis indicated that the succession of Bacillus was positively correlated with the enrichment of multiple core esters. Overall, this study demonstrates that targeted Bacillus bioaugmentation regulates microecological dynamics and flavor biosynthesis, providing a theoretical foundation for Xiaoqu Baijiu quality enhancement.