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Wheat Qu plays the role of saccharification fermentation, providing microorganisms and flavor in the fermentation of huangjiu , and the use of functional microorganisms to fortify wheat Qu is becoming increasingly popular. Yet, the mechanisms promoting microbial successions of wheat Qu remain unclear. In this study, we first correlated microbial community succession with physicochemical factors (moisture, temperature, acidity, glucoamylase and amylase) in inoculated raw wheat Qu (IRWQ) with Saccharopolyspora rosea. The Mantel test was performed to investigate the significance and found that temperature (r = 0.759, P = 0.001), moisture (r = 0.732, P = 0.006), and acidity (r = 0.712, P = 0.017) correlated significantly with the bacterial community in phase 1 (0–40 h). Meanwhile, temperature correlated significantly with the fungal community in phases 1 and 2 (40–120 h). To confirm the effect of temperature on microbial communities, the artificial reduction of bio-heat (37°C) in IRWQ also reduced the relative abundance of heat-resistant microorganisms including Bacillus and Saccharopolyspora. A higher abundance of Saccharopolyspora (87%) in IRWQ was observed following biofortified inoculation of S. rosea , in which glucoamylase activity increased by 40% compared to non-inoculated raw wheat Qu (NIRWQ) (1086 U/g vs 776 U/g). Finally, the IRWQ was employed to mechanized huangjiu fermentation and it was found to reduce the bitter amino acid and higher alcohol content by 27% and 8%, respectively, improving the drinking comfort and quality of huangjiu. [ABSTRACT FROM AUTHOR]

[Display omitted] • P. pentosaceus , W. paramesenteroides , R. emersonii, B. spectabilis were dominant in Daqu. • Four Saccharopolyspora species were dominant in wheat Qu. • Flavor metabolic pathways in Qu microbiota were reconstructed. • The dominant microbes in Qu may not be the main functional microbes. Daqu and wheat Qu are saccharification and fermenting agents in Chinese huangjiu and baijiu production. This study aimed to investigate the difference between Daqu and wheat Qu in physicochemical indices, microbial communities, functional genes, and the metabolic network of key microbes responsible for flavor synthesis by whole-metagenome sequencing and metabolite analysis. Herein, physicochemical indices indicated that compared with wheat Qu , Daqu exhibited higher protease and cellulase activity and acidity, and lower glucoamylase and amylase enzyme activity. Metagenomic sequencing reveals that although Daqu and wheat Qu community composition have significant differences at species level, they have similar functional genes. Daqu were enriched in Pediococcus pentosaceus , Weissella paramesenteroides , Rasamsonia emersonii and Byssochlamys spectabilis (22.48% of the total abundance), while wheat Qu harbored greater abundances of Saccharopolyspora (54.78%, Saccharopolyspora rectivirgula , Saccharopolyspora shandongensis , Saccharopolyspora hirsuta , Saccharopolyspora spinose , and Saccharopolyspora erythraea). From a functional perspective, the important functions of Daqu and wheat Qu are both amino acid metabolism and carbohydrate metabolism. Meanwhile, a combined analysis among microbiota, functional genes, and dominant flavors indicated S. shandongensis , S. rectivirgula , and S. spinose might be the main contributor to the synthesis of flavor compounds in wheat Qu , while R. emersonii , W. paramesenteroides , Leuconostoc citreum , Leuconostoc mesenteroides , Weissella cibaria and P. pentosaceus may make the greatest contribution to flavor compounds synthesis in Daqu. This study reveals the microbial and functional dissimilarities of Daqu and wheat Qu , and helps elucidating different metabolic roles of microbes during flavor formation. [ABSTRACT FROM AUTHOR]