Associations between the intratumoral microbiome and the host transcriptome in bladder cancer and their implications for prognostic prediction.

Intratumoral microbes significantly influence tumor progression, yet their specific roles and host interactions in bladder cancer (BLCA) remain elusive. Integrating 16 S rRNA sequencing from an in-house cohort with TCGA data, we identified Methylobacterium as prominently enriched in adjacent non-tumor tissues and tightly correlated with host transcriptomic alterations. Through LASSO regression, we constructed and externally validated a Methylobacterium-associated four-gene prognostic signature (SLC1A6, BCHE, TXNRD1, CFL2). The model robustly stratified patient outcomes; high-risk patients exhibited significantly worse survival, characterized by an immunosuppressive microenvironment with elevated M2 macrophages, regulatory T cells, and higher TIDE scores indicating immune evasion. Crucially, in vitro experiments suggested that Methylobacterium supernatant exerted tumor-suppressive effects, profoundly inhibiting BLCA cell proliferation and colony formation while modulating host gene expression (downregulating BCHE and CFL2). Collectively, this study unveils the protective potential of intratumoral Methylobacterium and proposes a novel microbe-derived signature for predicting BLCA prognosis and immune status, providing new insights into microbiota-host crosstalk for future therapeutic strategies.