In the process of medium-high temperature Daqu fermentation, the water mass transfer in the porous medium of Daqu block is conducive to the enhancement of the adaptability of microorganisms, among which the membrane-producing microorganisms have the functions of raw material decomposition, promoting metabolic coordination, and regulating the fermentation environment.As a typical membrane-producing microorganism, the regulatory mechanism of Bacillus on Daqu fermentation remains to be studied.In this study, the microbial structure during Daqu fermentation was investigated by amplicon-sequencing.It was found that Bacillus was dominant in the high-temperature fermentation stage, and the relative abundance was 10 times higher than that in the early stage of Daqu fermentation.Three Bacillus strains were isolated from Daqu under high-temperature conditions, their biomass changes were monitored by QPCR, and their biofilm formation ability was analyzed by crystal violet detection.Results showed that the biomass of Bacillus amyloliquefaciens GKT04 was stable and relatively higher under high temperature and co-culture conditions, and its biofilm formation ability was more than double that of the other two strains.Furthermore, the exopolysaccharide composition of Bacillus amyloliquefaciens GKT04 was detected by ion chromatography, and the results showed that Bacillus amyloliquefaciens GKT04 could produce mannose (98.5 mg/L) and rhamnose (76.4 mg/L) during the fermentation process, which enhanced the viscosity, stability, and water retention of the biofilm.In the simulated Daqu fermentation experiment, the moisture content of Daqu at the end of fermentation was relatively increased by 20% by Bacillus amyloliquefaciens GKT04.SEM observation showed that Bacillus amyloliquefaciens GKT04 could make the surface of Daqu substrate covered with more abundant biofilms, thereby enhancing the water retention of Daqu.This study provides a new understanding of the physiological mechanism of Bacillus regulating Daqu fermentation and provides a new perspective for strengthening Daqu fermentation to improve fermentation quality.
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