Metatranscriptomics Analysis of Changes in the Structure and Function of Active Microbial Community in Fermented Grains of Chinese Strong-flavor Baijiu

In this study, metatranscriptomics was used to analyze the diversity, succession and differentially transcribed genes of the active microbial community in fermented grains during the main fermentation period of Chinese strong-flavor baijiu (at days 3, 7 and 25). The results showed that the active microbial community was composed of 6 kingdoms, 124 phyla, 195 classes, 2824 genera, and some unknown or unidentifiable species. The identifiable organisms were mainly composed of bacteria and fungi. As fermentation proceeded, the relative content of fungi decreased from 42.8% to 0.01%, and the content of bacteria increased from 17.7% to 56.3%. Firmicutes and Ascomycota were the major phyla that drove changes in the composition of bacterial and fungal communities, respectively. The numbers of differentially expressed genes among three fermentation times were 6895 (3 d vs 7 d), 2640 (7 d vs 25 d) and 6124 (3 d vs 25 d), respectively. During the fermentation process, the number of down-regulated differential genes was significantly greater than that of up-regulated differential genes. From days 3 to 7 of fermentation, the up-regulated differential genes were significantly enriched in the metabolism of sugars and alcohols. During the whole major fermentation period, the down-regulated differential genes were mainly enriched in cell parts or related biological processes. The results of this study will provide basic data and theoretical support for in-depth understanding of the solid-state brewing mechanism of Chinese strong-flavor baijiu.