Deciphering the environmental response and assembly of rare and abundant taxa in zaopei employing daqu produced by different pressing patterns

Baijiu fermentation relies on complex microbial communities within zaopei, which are significantly shaped by the microbial starter daqu. This study investigated the rare and abundant taxa composition, and flavor characteristics of zaopei (fermented grains) employing Nongxiangxing daqu produced by different pressing patterns (mechanically pressed, artificially pressed) from microbial ecology perspective. Then, the origin, environmental response, assembly patterns and driving factors of rare and abundant taxa were revealed. The results indicated that both Lactobacillus and Acetobacter consistently dominated in rare bacteria and abundant bacteria of zaopei, the dominant abundant fungi were Thermoascus and Issatchenkia, while the dominant rare fungi were Aspergillus and Pichia. The microbial community of zaopei was significantly influenced by fungi originating from daqu, according to Fast expectation-maximization microbial source tracking (FEAST) analysis. Moreover, daqu significantly influenced the assembly process of abundant fungi taxa in zaopei, with the mechanically pressed daqu (MDQ) increased the proportion of heterogeneous selection. Moreover, water, starch and ethanol contents were important factors driving the rare bacteria assembly. Co-occurrence network analysis indicated that artificially pressed daqu (ADQ) enhanced microbial interactions in zaopei, which were closely related to rare bacteria. Meanwhile, Spearman's correlation between microorganisms and differential flavor compounds showed that fungal taxa (abundant Clavispora, rare Pichia and rare Issatchenkia) played a dominant role in flavor synthesis. These results contributed to a better understanding of the functional contributions of rare and abundant taxa in baijiu fermentation and provided theoretical support and technical guidance for regulating baijiu quality.