Large-scale microbiome analysis reveals bacterial community characteristics in typical Chinese herbal slices

Chinese herbal slices (CHSs) are closely associated to microorganisms, whether they are endophytic or epiphytic in plants, or introduced during processing. In this study, the structures and predicted functions of microbial communities in 150 batches of samples from five types of CHSs were investigated by combining pure culture and 16 S rDNA amplicon sequencing. Bile-salt-tolerant gram-negative bacteria were detected in 56.0% of samples, and Salmonella was detected in two batches of Glycyrrhiza slices and in one batch of Rheum slices. The main genera from the Enterobacteriaceae, Bacillaceae, Fibrobacteraceae, and Pseudomonadaceae families were assessed in typical colonies. Amplicon sequencing identified 1200 bacterial genera, including some pharmacopeial-controlled bacteria and many beneficial endophytes of medicinal plants. Around 65% of the genera co-occurred in all five CHSs. In clustering based on different algorithms, the samples from each CHS type were relatively clustered, with some overlap. Ranked from highest to lowest diversity, the CHSs were Rheum, Angelica, Astragalus, Codonopsis, and Glycyrrhiza. Each CHS had its indicator species. Functional annotations suggest that potential microbial transformation uses CHSs as substrates and microbial communities as transformants. Overall, it was demonstrated that, based on their complementary advantages, high-throughput sequencing technology and traditional pure-culture technology together can fully assess the microbial load of CHSs and reduce the misdetection rate. We observed large microbial communities in typical CHSs, demonstrating differences and similarities among different CHS types. These results provide a reference for establishing new microbial limit criteria for CHSs and highlight the importance of further correlating CHS microbial community structure and function.