Bacterial warfare is associated with virulence and antimicrobial resistance

Abstract Bacteria have evolved a diverse array of mechanisms to inhibit and kill competitors, commonly known as bacterial weapons. However, why some bacteria carry weapons while others do not remains poorly understood. Here we explore this question using the bacteriocins of E. coli as a model system, which are both well studied and have large well-annotated genomic resources. While bacteriocins are found widely across E. coli strains, we find that carriage is particularly associated with pathogenic extra-intestinal (ExPEC) strains, including many clinically-important pandemic strains. These pathogenic strains commonly carry large plasmids that encode the bacteriocins but also virulence factors, including siderophores, and antimicrobial resistance mechanisms. Across all E. coli strains, we find many orphan immunity proteins, which protect against bacteriocins and suggest that bacterial warfare is important in nature. We also present evidence that bacteriocin toxins readily move between strains via plasmid transfer and even between plasmids via transposons. Finally, we show that several E. coli bacteriocins are widely shared with the pathogen Salmonella enterica , further cementing the link to virulence. Our work suggests that the bacteriocins of E. coli are important antibacterial weapons for dangerous antimicrobial-resistant strains.