Effect of lactic acid bacteria on the structure and potential function of the microbial community of Nongxiangxing   Daqu

Abstract OBJECTIVES: The microbial community structure of the saccharifying starter, Nongxiangxing Daqu（Daqu）, is a crucial factor that determines the quality of Baijiu. lactic acid bacteria (LAB), the dominant microorganisms in the Daqu. The present study investigated the effects of LAB on the microbial community structure and its contribution to microbial community function during the fermentation of Daqu. RESULTS: Box-line variance analysis shows that LAB showed a significant stage-specific succession pattern during Daqu fermentation. The LEfSe analysis and the random forest learning algorithm identified LAB as vital differential microorganisms during Daqu fermentation. The correlation co-occurrence network constructed based on Spearman's rank correlation coefficients showed aggregation of LAB and Daqumicroorganisms, indicating LAB’s significant position in influencing the microbial community structure. LAB showed negative correlations with Bacillus, Saccharopolyspora, and Thermoactinomycesbut positive correlations with Issatchenkia, Candida, Acetobacter, and Gluconobacter. The predicted genes of LAB enriched 20 functional pathways during Daqu fermentation, including Biosynthesis of amino acids, Alanine, aspartate and glutamate metabolism, Valine, leucine and isoleucine biosynthesis and Starch and sucrose metabolism, which suggested that LAB had the functions of polysaccharide metabolism and amino acid biosynthesis. CONCLUSION: Thus, the study indicates that LAB is important in determining the composition and function of Daqu microorganisms，and also suggests that LAB are closely related to the production of nitrogenous flavor substances in Daqu. The study provides a foundation for further exploring the function of LAB and the regulation of Daqu quality.