Illuminating Anaerobic Microbial Community and Cooccurrence Patterns across a Quality Gradient in Chinese Liquor Fermentation Pit Muds

Fermentation pit mud, an important reservoir of diverse anaerobic microorganisms, is essential for Chinese strong-aroma liquor production. Pit mud quality, according to its sensory characteristics, can be divided into three grades: degraded, normal, and high quality. However, the relationship between pit mud microbial community and pit mud quality is poorly understood, as are microbial associations within the pit mud ecosystem. Here, microbial communities at these grades were compared using Illumina MiSeq sequencing of the variable region V4 of the 16S rRNA gene. Our results revealed that the pit mud microbial community was correlated with its quality and environmental factors. Species richness, biodiversity, and relative and/or absolute abundances ofClostridia ,Clostridium kluyveri ,Bacteroidia , andMethanobacteria significantly increased, with corresponding increases in levels of pH, NH4 + , and available phosphorus, from degraded to high-quality pit muds, while levels ofLactobacillus , dissolved organic carbon, and lactate significantly decreased, with normal samples in between. Furthermore, 271 pairs of significant and robust correlations (cooccurrence and negative) were identified from 76 genera using network analysis. Thirteen hubs of cooccurrence patterns, mainly under theClostridia ,Bacteroidia ,Methanobacteria , andMethanomicrobia , may play important roles in pit mud ecosystem stability, which may be destroyed with rapidly increased levels of lactic acid bacteria (Lactobacillus ,Pediococcus , andStreptococcus ). This study may help clarify the relationships among microbial community, environmental conditions, and pit mud quality, allow the improvement of pit mud quality by using bioaugmentation and controlling environmental factors, and shed more light on the ecological rules guiding community assembly in pit mud.