Unraveling the core microbial succession during the moromi fermentation of cantonese soy sauce: An amplicon sequencing approach.

Understanding the microbial successional dynamics and their functional contributions is crucial for optimizing the traditional brewing process of fermentation. In this study, an integrated bioinformatic approach, combining co-occurrence networks, machine learning, and PICRUSt2 functional prediction, was employed to systematically decipher the bacterial and fungal community assembly patterns during brine fermentation. High-throughput sequencing data were normalized using total sum scaling (TSS), and the relationships between microbial succession and physicochemical parameters were evaluated through redundancy analysis (RDA). Taxonomic analysis revealed a "double-stage" successional model: the bacterial community transitioned from Weissella (35.0%) and Enterobacter (24.0%) to a mature state dominated by Lactobacillus (24.8%) and Staphylococcus (17.6%), while the fungal community underwent a structural shift from the high dominance of Aspergillus (97.8%) to stress-tolerant yeasts, primarily Zygosaccharomyces (48.4%). Co-occurrence network analysis indicated that the bacterial network reached peak complexity and connectivity in the middle stage, whereas the fungal network followed a unique "collapse-reconstruction" trajectory. By utilizing the Random Forest algorithm, a parsimonious biomarker suite (36 bacterial and 9 fungal genera) was identified, achieving high predictive accuracy for bacterial (78.6%, 95% CI: 59%-92%, Kappa = 0.62) and fungal (85.7%, 95% CI: 55%-89%, Kappa = 0.51) models on internal batch-level validation datasets. Functional prediction further elucidated that early-stage bacterial Amplicon Sequence Variants (ASVs) are positively correlated with the degradation of macromolecules via enhanced amino acid and carbohydrate metabolism, suggesting a putative metabolic cooperation with Aspergillus, while late-stage microbiota suggested a potential contribution to survival and flavor enrichment through upregulated pyruvate metabolism and fatty acid biosynthesis. These findings quantify the successional dynamics of core taxa and biomarkers at the ASV level and provide a robust theoretical foundation for monitoring and modulating traditional fermentation processes to ensure quality consistency and safety.