Abstract: In this study, high-throughput sequencing technology was employed to analyze the differences in bacterial community structure among three grades (high, medium and low) of pit mud for nongxiangxing baijiu, differing in the quality of resulting liquor. Correlational analysis was conducted between microbial communities and physicochemical indicators to provide a scientific basis for pit mud quality assessment. The results showed that the high-grade pit mud exhibited greater bacterial community diversity, where the core functional bacteria (e.g., Brevefilum, Caproiciproducens) predominated and showed a significant positive correlation with key physicochemical indicators such as ammonia nitrogen and humus levels (P < 0.01). The pH of the pit mud was close to 7. It presented the metabolic characteristics of high hexanoic acid and low lactic acid contents. The low-grade pit mud was dominated by genera such as Pseudomonas and Stenotrophomonas, which were negatively correlated with ammonia nitrogen and humus levels and other key physiochemical indicators (P < 0.01). The microbial community in the low-grade mud was less diverse, and featuring a lower pH and reduced nutrient levels, suggesting that the pit mud micro-ecosystem was either in an initial stage of domestication or underwent significant microbial community degradation. This study reveals the correlation between the bacterial community structure in pit mud and its physicochemical indicators, clarifying the microbiological basis for quality variations among different grades of pit mud, thereby providing a theoretical basis for the scientific evaluation of pit mud quality and the optimization of pit management.

Key words: quality of pit mud; high-throughput sequencing; physicochemical factors; bacterial community; functional microorganisms