Background: Com ruou is a traditional Vietnamese fermented glutinous rice product prepared using artisanal starter cultures (banh men). The fermentation process is largely empirical and information on microbial succession using culture-independent methods remains limited. 
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Methods: Amplicon sequencing targeting the bacterial 16S rRNA (V3-V4) and fungal ITS regions was applied to evaluate microbial community dynamics during fermentation. Samples were collected at three stages: starter (0 h), 36 h and 72 h fermentation. Alpha and beta diversity analyses were conducted and taxonomic composition was assessed at multiple levels. 
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Result: Microbial diversity increased during fermentation, indicating community restructuring. Bacterial communities shifted from lactic acid bacteria-associated taxa in the starter to Proteobacteria- and Bacillus-enriched populations at later stages. Genera such as Pantoea, Acinetobacter and Bacillus increased in relative abundance during fermentation. The fungal community was initially dominated by R. arrhizus and declined over time, while fermentative yeasts including Kodamaea and Wickerhamomyces increased during early fermentation. Ethanol concentration reached 4.595% (v/v) at 72 h, accompanied by pH reduction, reflecting active fermentation.

Metabarcoding Insights into Microbial Community Dynamics during Traditional Vietnamese Rice Fermentation (Com Ruou)