This study was performed in order to understand the differences in bacterial communities and physicochemical indicators between bottom and wall pit mud for nongxiangxing baijiu. Five physicochemical indicators of pit mud were analyzed. High-throughput sequencing technology was used to investigate the bacterial communities, and correlation analysis was carried out between bacterial communities and physicochemical indicators. The results showed that the pH and catalase activity in bottom pit mud were significantly higher than those in wall pit mud (P < 0.05), while the opposite was true for ammonium nitrogen content (P < 0.05). The dominant bacterial phyla in pit mud were Firmicutes, Bacteroidetes, and Synergistetes. The dominant genera in bottom pit mud were Hydrogenispora, Caproiciproduces, Aminobacterium, and Proteiniphilum, the relative abundance of Hydrogenispora being significantly higher than that in wall pit mud (P < 0.05). The dominant genera in wall pit mud were Capriocipiroducens, Lactobacillus, Syntrophaceticus, and Aminobacterium, the relative abundance of Capriocipiroducens, Lactobacillus and Syntrophaceticus being significantly higher than that in bottom pit mud (P < 0.05). The physicochemical indicators and bacterial communities in bottom and wall pit mud were different. Among the physicochemical indicators, pH had the greatest impact on the bacterial community in bottom pit mud, and Hydrogenispora was the iconic genus of bacteria in pit bottom mud. The relative abundance of enzymes involved in acid metabolism was higher in pit wall mud. In conclusion, there were spatial differences in the bacterial communities between bottom and wall pit mud, which could have an important impact on the fermentation of baijiu.

In order to clarify the succession pattern and potential functions of the microbial communities in fermented grains for Nongxiangxing baijiu, high-throughput sequencing was used to investigate the dynamic change of microbial community structure, and the correlations between microbial community structure and physicochemical indicators were analyzed at different fermentation stages. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) was used to predict the potential functions of microbial communities in fermented grains. The results showed that Firmicutes, Proteobacteria, Actinobacteriota, Ascomycota, and Basidiomycota were the dominant phyla in fermented grains. The dominant genera were Lactobacillus, Bacillus, Staphylococcus, Thermoactinomyces, Kazachstania, Wickerhamomyces, Penicillium, Candida, Aspergillus, Meyerozyma, Debaryomyces, with Lactobacillus, Kazachstania and Wickerhamomyces being the absolutely dominant ones. The contents of reducing sugar and starch showed a significantly positive correlation with 8 bacterial genera (P < 0.05). Acidity and moisture content showed a significantly negative correlation with 10 bacterial genera. Some fungi were significantly correlated with physicochemical indicators. PICRUSt analysis showed that the relative abundance of functional enzymes was significantly different at different fermentation stages, and the dominant microorganisms in fermented grains participated in glycolysis, acid metabolism and ethanol synthesis to form a complete metabolic chain, indicating that the microbial community succession of fermented grains could be the major reason for the differences in metabolism at different fermentation stages. The findings of this study would provide a theoretical basis for the study of the metabolic mechanisms of microorganisms used for baijiu brewing.