Mutational signature in colorectal cancer caused by genotoxic pks + E. coli

Various species of the intestinal microbiota have been associated with the development of colorectal cancer 1 , 2 , but it has not been demonstrated that bacteria have a direct role in the occurrence of oncogenic mutations. Escherichia coli can carry the pathogenicity island pks , which encodes a set of enzymes that synthesize colibactin 3 . This compound is believed to alkylate DNA on adenine residues 4 , 5 and induces double-strand breaks in cultured cells 3 . Here we expose human intestinal organoids to genotoxic pks + E. coli by repeated luminal injection over five months. Whole-genome sequencing of clonal organoids before and after this exposure revealed a distinct mutational signature that was absent from organoids injected with isogenic pks -mutant bacteria. The same mutational signature was detected in a subset of 5,876 human cancer genomes from two independent cohorts, predominantly in colorectal cancer. Our study describes a distinct mutational signature in colorectal cancer and implies that the underlying mutational process results directly from past exposure to bacteria carrying the colibactin-producing pks pathogenicity island.