Effect of Bacillus subtilis fortified inoculation on the microbial communities in different niches of Daqu.

Daqu is the fermentation starter of Baijiu, which is one of the six most renowned distilled spirits. Studies have found that Bacillus is one of the dominant microbial genera in Daqu, and Bacillus subtilis is known to produce amylase, an important enzyme that influences the quality of Daqu. This study aims to explore the influence of B. subtilis inoculation on the microbial community structure in different niches of Daqu. We studied the microbial community structure of the natural inoculated Daqu (i.e., control Daqu) and the fortified Daqu (i.e., B. subtilis-inoculated Daqu) by amplicon sequencing. Our results showed that compared with the control Daqu rind microbial community, the relative abundance of Bacillus, Aspergillus, Thermomyces, and Rasamsonia in the fortified Daqu rind microbial community increased, and the relative abundance of Weissella, Lactobacillus, Leuconostoc, and Pichia decreased. Compared with the control Daqu core microbial community, the relative abundance of Bacillus in the fortified Daqu core microbial community also increased, but the relative abundance of Pseudomonas and Paecilomyces decreased. The effect of B. subtilis inoculation on the rind microbial community of Daqu was more significant. In addition, the bacterial community of Daqu was more susceptible to the effect of the B. subtilis inoculation than was the fungal community of Daqu. The correlation between the bacterial community of Daqu and the fungal community of Daqu increased significantly after the B. subtilis inoculation. These results provide an important theoretical basis for the production of fortified Daqu.