The spatio-temporal diversity and succession of microbial community and its environment driving factors during stacking fermentation of Maotai-flavor baijiu

Stacking fermentation is an important stage of microbial expansion and enrichment in the brewing process of Maotai-flavor baijiu and has an important impact on quality. However, the structure and succession of microbial communities at different spatial points of fermented grains, as well as the key environmental factors driving community assembly, remain unclear. Here, we analyzed spatio-temporal similarities and differences in the microbial community structure and succession during 1-6 rounds of stacking fermentation of Maotai-flavor baijiu. The microbial diversity and richness in the pile center were higher than those at the pile surface. The dominant bacterial genus changed from Lactobacillus to Acetobacter, while the dominant fungal genus Pichia was gradually replaced by Candida, however, some microorganisms (Acetobacter, Thermoascus) could not occupy community dominance in both the pile surface and the pile center of fermented grains. Most of the biomarkers (Kroppenstedtia, Thermomyces, etc.) of the pile surface showed thermostable or thermophilic characteristics, while most biomarkers (Aspergillus, Hyphopicia, etc.) of the pile center were functional microorganisms. Furthermore, pH and moisture were the main environmental driving factors of community construction at the pile surface and the pile center, respectively, with starch and reducing sugars having a greater impact on the microbial community assembly of the pile center than that of the pile surface. The main differences in the metabolic pathways of the dominant bacterial genera of the pile surface and the pile center were concentrated around cell growth and death, amino acids, leading to enrichment and growth of microbial communities at the pile surface and nitrogen utilization at the pile center, respectively. This study reveals the spatio-temporal differences in microbial community structure, succession and corresponding environmental driving factors during stacking fermentation, which will provide guidance for regulating the microbial community diversity to produce high-quality Maotai-flavor baijiu.