Characterizing the regulation mechanism of microbial community and metabolites in multi-layer vinegar starter (Cuqu) via Muqu fortification strategy

Improving the quality of Cuqu is one of the necessary strategies increasing the quality and yield of fresh vinegar. Enhancing the consistency and characteristics of Cuqu is currently a prominent area of research. Here, we investigated the impact of fortified Muqu (FM) consisting of Bacillus velezensis and Bacillus subtilis on enhancing the quality of Cuqu compared to conventional Muqu (CM). Our results demonstrated that FM significantly increased the abundance of Bacillus by 1.85 to 8.19 times, as well as substantially elevated Kroppenstedtia abundance in Cuqu. Source Tracker analysis revealed a higher proportion of bacteria originating from FM in Cuqu compared to those derived from CM, indicating superior environmental adaptability for bacteria in the FM. Additionally, upregulation in expression levels of pyrazine-related key enzymes within Cuqu microbial communities was observed due to FM, resulting in a remarkable 39.70-fold increase in pyrazine compounds production. Multiphase detection technology confirmed that FM improved similarity in microbial community structure and function at different spatial positions within Cuqu. These results elucidated the regulatory function of FM in forming microbial communities and metabolic mechanisms within Cuqu, providing valuable insights for optimizing and predicting traditional fermentation processes in industrial production.