Abstract: In this study, high-throughput sequencing technology combined with network analysis and multivariate statistical analysis was used to analyze the prokaryotic microbial community diversity and microbial community networks, as well as the physicochemical factors affecting the microbial community in pit muds from the upper (PW-T), middle (PW-M) and lower (PW-U) layers of the wall, and from the bottom (PB) of a degraded fermentation pit used for the production of strong-flavor Baijiu. The results showed that the α and β diversity of the pit mud microbial community had obvious spatial heterogeneity in the degraded pit, and the process of degradation could proceed from top to bottom. As the depth of the pit was increased, the α diversity index of the pit mud microbial community showed a significant upward trend on the whole. Specifically, the Shannon index of microbial diversity followed the decreasing order of PW-U (3.38) > PB (2.51) > PW-M (1.09) > PW-T (0.33) (P < 0.05), and there was only one dominant phylum (Firmicutes, about 99%) in PW-T and PW-M, compared to six including Firmicutes, Bacteroidetes, and Euryarchaeota in PW-U and four in PB. All the pit muds had low water content (with an average of 32.7%), low pH (with an average of 4.42), and low available phosphorus content (with an average of 259.27 mg/kg), which had a great impact on the microbial community structure as determined by redundancy analysis (RDA). According to the co-occurrence network analysis, the genera in different classes (interclass) had a high co-occurrence incidence (accounting for 78.74% of the total correlation). The total content of the nine hubs in the co-occurrence network was very low (0%–2.84%), and it had a significantly positive correlation with the pH and water content of pit mud (P < 0.05 or P < 0.01); all hubs except Syntrophomonas showed a significantly negative correlation with Lactobacillus (P < 0.01). The pH of pit mud had a significantly positive or negative correlation with various physicochemical factors (P < 0.05) and a significantly positive correlation with Simpson index, which indicates that pH could be used as an indicator to evaluate pit mud quality. This study will provide theoretical support for further uncovering the degradation mechanism of pit mud, preventing the degradation of pit mud, and making high-quality artificial pit mud.

Key words: degradation of pit mud; spatial heterogeneity; microbial community diversity; microbial community network; Chinese strong-flavor Baijiu; high-throughput sequencing technology