Thresholded acidity-oxygen stress activates Acetilactobacillus jinshanensis and drives a shift toward deterministic...

Multi-round stacking fermentation links successive production rounds with pit fermentation in Moutai-flavor Baijiu, but quantitative indicators of microbial restructuring remain unclear. This study combined physicochemical monitoring, metagenomics, metatranscriptomics and quantitative polymerase chain reaction across 207 samples from three successive stages. Increasing acidity and lactic acid, starch consumption and late-stage community convergence characterized the stage sequence. Fitted community-displacement relationships showed acidity turning points near 1.0-1.2, whereas no universal oxygen threshold was supported. A composite stress index integrating acidity, acetic acid, lactic acid and inverse oxygen showed a pooled Acetilactobacillus jinshanensis abundance turning point near 0.27. This relationship differed among stages and heaps and did not establish a universal activation threshold. Adding the index did not improve between-team abundance prediction under the evaluated models. Community-level transcripts showed selective redistribution of acid-homeostasis, proton-transport, chaperone, organic-acid-metabolism and redox-related functions. Assembly analyses indicated stronger homogeneous-selection signals, whereas network associations varied by stage without demonstrating a universal hub or experimentally verified ecological role. These observations identify candidate transition windows in the studied stacking system and require process-specific validation before operational application.