Common gut bacteria can induce eukaryotic chromosomal instability in vivo, according to a study published in a recent issue of the Proceedings of the National Academy of Sciences USA.Up to 34% of commensal Escherichia coli strains isolated from human faeces in high-income countries contain pks, a genomic island encoding a cluster of non-ribosomal peptide synthetases and polyketide synthetases that are involved in the production of the genotoxin colibactin.