Abstract: This study explored the effect of Bacillus subtilis JP1, isolated from the fermentation process of nongxiangxing baijiu, on the assembly and succession of microbial communities in fermented grains (Jiupei). A mixed-culture fermentation system was constructed using Jiupei and yellow water from nongxiangxing baijiu production. A bio-perturbation experiment was conducted by adding B. subtilis JP1 to the system. Amplicon sequencing combined with null model analysis was used to investigate the structure, composition and assembly process of microbial communities. R language was employed to calculate the environmental niche breadth of microorganisms to analyze potential reasons for changes in microbial community assembly. The results showed that compared with the control group, B. subtilis JP1 reduced the microbial diversity during fermentation while increasing the relative abundance of ethanol-producing microorganisms. Additionally, B. subtilis JP1 decreased the environmental niche breadth of the microbial community, leading to a significant increase in the number of rare and conditionally rare taxa. The interactions among microorganisms were enhanced, and the complexity of the microbial network was increased. These changes collectively influenced the assembly process of the microbial community during fermentation. The addition of B. subtilis JP1 increased the contribution of heterogeneous selection for bacteria and homogeneous selection for fungi to the microbial community assembly process. Furthermore, it accelerated bacterial succession while slowing down fungal succession. This study elucidates the mechanism of the effect of B. subtilis on the establishment of microbial communities in fermented grains for nongxiangxing baijiu, providing a theoretical basis for the targeted regulation of Bacillus during the brewing process of nongxiangxing baijiu.

Key words: nongxiangxing baijiu, Bacillus subtilis, environmental niche breadth, community assembly