Quantitative microbiome analysis reveals the microbial community assembly along with its correlation with the flavor substances during the manufacturing process of Qingzhuan brick tea at an industrial scale

Several studies have shown that microorganisms are key factors in the transformation of dark tea chemicals. However, these studies have mainly used relative abundance to study the diversity of the microbial community during tea fermentation. The dynamics of microbial density and assembly of abundant and rare microbes remains poorly understood. In this study, the entire manufacturing process of Qingzhuan brick tea (QBT) was studied at an industrial scale. The succession of both bacterial and fungal communities was investigated using high-throughput sequencing along with quantitative PCR (qPCR) analysis. Changes in non-volatile flavor components, including soluble sugar (SS), total polyphenols (TP), nine tea catechins, caffeine, 21 free amino acids, and three tea pigments were detected. Mantel test showed that both bacterial and fungal community structures were significantly correlated with environmental variables during the microbial fermentation process but not during the aging process. The absolute microbial density was calculated based on qPCR gene copies and relative abundance. The quantitative microbiota network showed that dominant microbes constitute the basic skeleton of the network, while rare microbes have a stronger correlation with various flavor contents. These results help to understand the assembly of microbial communities and their role in the formation of tea flavor substances.