Directed regulation of high-temperature Daqu microbiota and metabolites using synthetic communities

High-temperature Daqu (HTD) plays a critical role in shaping the microbial communities and metabolic profiles during the production of Jiangxiang-flavor Baijiu (JXFB). However, directed regulation of HTD properties remains challenging due to complex interactions among biotic and abiotic factors throughout the process. This study investigated the impact of Bacillus strains, including individual strains and synthetic microbial communities (SynMCs) composed of multiple strains, when combined with Monascus floridanus or Muqu, on the microbiota and metabolite profiles of HTD. Our results demonstrated that both functional strains and their combinations significantly influenced the microbial community structure and key flavor compounds. Bacillus-based interventions significantly increased pyrazine content, particularly in SynMCs supplemented with Muqu. Samples treated with Monascus and Bacillus exhibited greater consistency in organic acids, non-volatiles, and volatiles compared to other treatments, indicating that interkingdom interactions between fungi and bacteria enhance flavor control. The similarity index among fungal communities reached 44.44 %, while bacterial community similarity was only 25.51 %, and cluster analysis revealed a directional pattern in fungal succession. Co-occurrence network analysis indicated that high-yielding metabolite communities exhibited elevated average degree, average path length, and clustering coefficient, suggesting a higher connection density and information transfer, thereby promoting metabolite production. Kroppenstedtia displayed varied functions across different treatments, indicating that specific microbial combinations modulate the ecological roles of key taxa, resulting in changes in community structure and metabolism. These findings provide a theoretical basis for more controlled HTD fermentation, potentially enhancing the quality of JXFB.