Rare taxa as the microbial taxa more sensitive to environmental changes drive alterations of daqu microbial community structure and function

Microbial interactions and environmental conditions determine the evolution of microbial communities and their functions during Nongxiangxing daqu (daqu) fermentation. In this study, the sensitivity of rare microbial taxa, conditionally rare-abundant microbial taxa and abundant microbial taxa, to environmental changes, as well as the impact of their presence on the microbial community structure and function during daqu fermentation were elucidated by using high-throughput sequencing technology combined with environmental and volatile metabolites analysis. The results indicated that rare taxa, which were the predominant microbial taxa, were more heterogeneous during the daqu fermentation process. It is necessary to note that rare taxa were more sensitive to changing environmental conditions. The microbial molecular ecological network and within-module connectivity and among-module connectivity analysis showed that most of the key nodes (∼63% of operational taxonomic units) located in the networks determining microbial interactions belong to rare taxa. Furthermore, rare taxa were significantly associated with more volatile metabolites, and rare taxa were particularly important for the synthesis of pyrazines and alcohols. The present study demonstrated that rare taxa, as the microbial taxa more susceptible to environmental variation, drive alterations in the structure of microbial communities and their functions.