Summary
Temperate phages are pervasive in bacterial genomes, existing as vertically-inherited islands called prophages. Prophages are vulnerable to the predation of their host bacterium by exogenous phages. Here we identify BstA, a novel family of prophage-encoded phage defence proteins found in diverse Gram-negative bacteria. BstA drives potent suppression of phage epidemics through abortive infection. The bstA-encoding prophage itself is not inhibited by BstA during lytic replication due to a self-immunity mechanism driven by the anti-BstA (aba) element, a short stretch of DNA within the bstA locus. Phage-targeting by distinct BstA proteins from Salmonella, Klebsiella and Escherichia prophages is functionally interchangeable, but each possesses a cognate aba element. The specificity of the aba element ensures that immunity is exclusive to the replicating prophage, and cannot be exploited by heterologous BstA-encoding phages. BstA allows prophages to defend their host cells against exogenous phage attack, without sacrificing their own lytic autonomy.
Competing Interest Statement
The authors have declared no competing interest.