Abstract
Abortive infection, during which an infected bacterial cell commits altruistic suicide to destroy the replicating bacteriophage and protect the clonal population, can be mediated by toxin-antitoxin systems such as the Type III protein-RNA toxin-antitoxin system, ToxIN. A flagellum-dependent bacteriophage of the Myoviridae, Phi TE, evolved rare mutants that "escaped" ToxIN-mediated abortive infection within Pectobacterium atrosepticum. Wild-type Phi TE encoded a short sequence similar to the repetitive nucleotide sequence of the RNA antitoxin, ToxI, from ToxIN. The Phi TE escape mutants had expanded the number of these "pseudo-ToxI" genetic repeats and, in one case, an escape phage had "hijacked" ToxI from the plasmid-borne toxIN locus, through recombination. Expression of the pseudo-ToxI repeats during Phi TE infection allowed the phage to replicate, unaffected by ToxIN, through RNA-based molecular mimicry. This is the first example of a non-coding RNA encoded by a phage that evolves by selective expansion and recombination to enable viral suppression of a defensive bacterial suicide system. Furthermore, the Phi TE escape phages had evolved enhanced capacity to transduce replicons expressing ToxIN, demonstrating virus-mediated horizontal transfer of genetic altruism.