Small-molecule metabolites from the gut microbiota might contribute to the progression of colorectal cancer (CRC) via DNA damage. For example, some strains of Escherichia coli produce the genotoxin colibactin, which alkylates and crosslinks DNA, leading to double-strand DNA breaks; colibactin has been positively associated with progression of human CRC. However, the existence of genotoxins from other gut bacteria remains underexplored.