Helicobacter pylori (H. pylori) infection has been considered as the main causal factor in gastric carcinogenesis, but other bacterial species may also play an important role in pathophysiology of gastric cancer. The aim of the study was to explore the link between gastric cancer prognosis and the mucosal microbial community in tumorous and adjacent gastric tissue. The bacterial profile was analysed using 16S sequencing (V1–V2 region). Microbial differences were mostly characterized by lower relative abundances of H. pylori in tumorous gastric tissues. Bacterial community and outcome data analysis revealed the genus Fusobacterium and Prevotella significantly associated with worse overall survival in gastric cancer patients. In particular, Fusobacterium was associated with significant increase in hazard ratio in both univariable and multivariable analysis and independently validated using TCMA data. Phylogenetic biodiversity of Fusobacterium species in the stomach revealed F. periodonticum as the most prevalent in healthy subjects, while F. nucleatum was most abundant in patients with gastric cancer. Bacterial community network analysis in gastric cancer suggests substantial complexity and a strong interplay between F. nucleatum and Prevotella. In summary, mucosal microbial community in the stomach was associated with worse overall survival in gastric cancer patients. Strongest negative impact on prognosis was linked to the abundance of F. nucleatum in tumorous specimens, suggesting its translational relevance in management of gastric cancer patients.

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The cellular heterogeneity within a variety of solid tumors is influenced by several type of tumor-associated bacteria through yet poorly understood mechanisms. Unbiased genomic analysis revealed that right-sided colorectal tumors with poorer prognosis are preferentially populated with species related to Escherichia coli, including strains that are producing colibactin. By applying metabolomic profiling in situ, the presence of colibactin-producing Escherichia coli (CoPEC) was identified to establish a high-glycerophospholipid microenvironment within right-sided colorectal tumors that are bearing mutations in either APC or KRAS. Using spatial approaches, we revealed that bacterial microniches are poorly infiltrated with CD8+ T cells. The aforementioned alterations in lipid metabolism negatively correlated with immunomodulatory and neurotrophic factors among which the human regenerating family member 3 alpha gene (REG3A). Accordingly, the loss of its ortholog enhances growth at the proximal colon of tumors with a microenvironment that impedes immune surveillance and shares similarities to human right-sided colorectal tumors. This work clarifies how the presence of colibactin-producing bacteria may locally establish tumor heterogeneity for lipid metabolism to promote cancer progression and provide unique insights both for therapeutic intervention and enabling basic research into the mechanisms of microbiota-host interaction.

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