Isolation of a metabolite from the pks island provides insights into colibactin biosynthesis and activity.

Colibactin is a structurally uncharacterized, genotoxic natural product produced by commensal and pathogenic strains of E. coli that harbor the pks island. A new metabolite has been isolated from a pks(+) E. coli mutant missing an essential biosynthetic enzyme. The unusual azaspiro[2.4] bicyclic ring system of this molecule provides new insights into colibactin biosynthesis and suggests a mechanism through which colibactin and other pks-derived metabolites may exert genotoxicity.