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

Various species of the intestinal microbiota have been associated with the development of colorectal cancer.sup.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.sup.3. This compound is believed to alkylate DNA on adenine residues.sup.4,5 and induces double-strand breaks in cultured cells.sup.3. Here we expose human intestinal organoids to genotoxic pks.sup.+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.