Quorum sensing-associated acid adaptation in bacterial communities during pit fermentation of sauce-flavor Baijiu

Sauce-flavor Baijiu is produced by multi-round solid-state fermentation under progressively increasing acidity, yet how bacterial communities adapt to this extreme acid stress and whether quorum sensing (QS)-associated features are involved remain unclear. Here, fermented grains from eight pit-fermentation rounds under both traditional and mechanized processes were analyzed by metagenomic sequencing and physicochemical profiling. The traditional process showed higher moisture, stronger and faster acidification, greater lactic acid accumulation, and more rapid depletion of reducing sugars and starch than the mechanized process. These conditions coincided with a sharper decline in bacterial α-diversity and convergence toward a community overwhelmingly dominated by Acetilactobacillus jinshanensis (>90%) in the traditional process, whereas the mechanized process maintained higher diversity and a multi-species core dominated by A. jinshanensis, Lactobacillus acetotolerans, Bacillus, and actinomycetes. Canonical correspondence analysis identified acidity (lactic acid) as a major environmental factor associated with these divergent trajectories. QS gene profiling revealed process-specific signatures, with the LuxS/AI-2-associated module being the most abundant QS-related feature and significantly enriched in the traditional process. Functional annotation uncovered coordinated enrichment of acid-adaptation genes (ATPF1A, clpP, ATPF1B, dnaK, and groEL) during mid-to-late stages under high acidity. Network analysis further highlighted tighter co-associations among A. jinshanensis, QS modules, and acid-adaptation genes, supporting a community-level QS-associated functional framework for ecological convergence. Collectively, this study links LuxS/AI-2-associated features to acid-adaptation capacity and A. jinshanensis dominance in high-acidity environment. These findings provide ecological insight into microbial resilience in high-acidity solid-state fermentations and offer QS-informed perspectives for future targeted validation in Baijiu production.