Characterization of microorganisms in fermented douchi in China

Abstract

ObjectiveThe aim of this study was to elucidate the microbial characteristics of fermented soybean paste （douchi） in China and explore the microbial interactions in douchi.MethodsThirty-seven representative douchi samples were collected from a Chinese market， and microbial information was obtained by metagenomic sequencing. Douchi samples were clustered and illustrated using non-metric multidimensional scaling. Permutational multivariate analysis of variance was used to evaluate microbial community differences among regions. Mantel tests were performed to analyze the relation between geographic distance and microbiome dissimilarity. Linear discriminant analysis effect size was used to determine the microbial features that most likely explained the differences between the regions. A network was constructed to analyze the interactions between microorganisms.ResultsThe results revealed a nearly significant difference in douchi microbial diversity across different regions， with higher microbial diversity observed in Central China. The Mantel test analysis demonstrated a strong correlation between microbial community distances in douchi and geographical distances. Among the bacteria present in douchi， the predominant phylum was Firmicutes （average abundance： 80.9%）， the most abundant order was Bacillales （average abundance： 66%）， and the most abundant genus was Bacillus （50.3%）. This study also found that beneficial bacteria and foodborne pathogens coexist in douchi. The main beneficial bacteria included Bacillus and various lactic-acid-producing bacteria. Foodborne pathogenic bacteria included Salmonella enterica， Bacillus cereus， Staphylococcus aureus， and Cronobacter sakazakiit. Within the species network， a potential synergistic relation was observed among Bacillales species， whereas competitive interactions were observed between Bacillales and other microbial orders， including Lactobacillales.ConclusionDouchi in China harbors a diverse array of microorganisms and exhibits significant regional variations and distinct features. Most products contain both beneficial and foodborne pathogenic bacteria.

Keywords

• douchi
• microorganism
• metagenomic sequencing