Metagenomic sequencing combined with physicochemical properties determination reveals microbial community and function different of low-temperature Daqu

Complex microorganisms of different types of low-temperature Daqu (LTD) play an important roles in the formation of flavors and qualities of light-flavor Baijiu (LFB) during fermentation. However, understanding the similarities and differences of taxonomic and functional diversity of the whole microorganisms among the three types of LTD still remains a major challenge. Here, metagenomic sequencing combined with culture-based methods and physicochemical indicators determination were used to study the three types of LTD used in the brewing of LFB. Our results revealed that the diversity of microorganisms in LTD was very high, and 1286 genera and 4157 species could be detected in all samples. Bacteria and fungi together constitute the main microbial in LTD, and the relative abundance ratio of bacteria to fungi in LTD was above 4:1. Houhuo and Hongxin have the highest relative abundance of bacteria and fungi in the three kinds of LTD, respectively. Bacillus (21.18%) and Bacillus licheniformis (17.45%) were the most abundant microorganisms in LTD at the level of genus and species, respectively. The different production temperatures of LTD have little effect on the microbial composition, but would lead to significant changes in the relative abundance of microorganisms in LTD. Among the three types of LTD, HH has the highest abundance of bacteria, fungi and lactic acid bacteria (LAB). The representative dominant species among each type of LTD showed high consistency in microbial functions. The microbes with higher relative abundance in Qingcha and Hongxin not only could produce specific flavor substances, but also had strong ability to degrade macromolecular substances in raw materials, and the representative dominant microorganisms in HH are more involved in metabolic pathways related to the production of flavor substances in liquor, which are highly complementary to the microbial functions of Qingcha. This study will significantly improve our understanding the effect of temperature on LTD quality and help guide the future exploration of microbial resources for the improvement of LTD products.