A bacterial toxin-antitoxin system as a native defence element against RNA phages

Bacteria have evolved a wide range of defence strategies to protect
themselves against bacterial viruses (phages). Most known bacterial
antiphage defence systems target phages with DNA genomes, which raises the
question of how bacteria defend against phages with RNA genomes. Bacterial
toxin-antitoxin systems that cleave intracellular RNA under stress could
potentially protect bacteria against RNA phages, but this has not been
explored experimentally. In this study, we investigated the role of a
model toxin-antitoxin system, MazEF, in protecting Escherichia coli
against two RNA phage species. When challenged with these phages, native
presence of mazEF moderately reduced population susceptibility and
increased survival of individual E. coli cells. Genomic analysis further
revealed an underrepresentation of the MazF cleavage site in genomes of
RNA phages infecting E. coli, indicating selection against cleavage. These
results show that, in addition to other physiological roles, RNA-degrading
toxin-antitoxin systems may serve as a native defence system against RNA
phages.