Convergent dysbiosis of gastric mucosa and fluid microbiome during stomach carcinogenesis

A complex microbiota in the gastric mucosa (GM) has been unveiled recently and its dysbiosis is identified to be associated with gastric cancer (GC). However, the microbial composition in gastric fluid (GF) and its correlation with GM during gastric carcinogenesis are unclear.We obtained GM and GF samples from 180 patients, including 61 superficial gastritis (SG), 55 intestinal metaplasia (IM) and 64 GC and performed 16S rRNA gene sequencing analysis. The concentration of gastric acid and metabolite nitrite has been measured.Overall, the composition of microbiome in GM was distinct from GF with less diversity, and both were influenced by H. pylori infection. The structure of microbiota changed differentially in GM and GF across histological stages of GC, accompanied with decreased gastric acid and increased carcinogenic nitrite. The classifiers of GC based on microbial markers were identified in both GM and GF, including Lactobacillus, Veillonella, Gemella, and were further validated in an independent cohort with good performance. Interestingly, paired comparison between GM and GF showed that their compositional distinction remarkably dwindled from SG to GC, with some GF-enriched bacteria significantly increased in GM. Moreover, stronger interaction network between microbes of GM and GF was observed in GC compared to SG.Our results, for the first time, revealed a comprehensive profile of both GM and GF microbiomes during the development of GC. The convergent microbial characteristics between GM and GF in GC suggest that the colonization of carcinogenic microbes in GM might derive from GF.