A HigB-like toxin promotes non-replicating Salmonella inside macrophages by inhibiting ribonuclease III

SUMMARY Many bacteria are often resistant to antibiotic treatment because they can slow down their growth rate, thereby attenuating the drug’s effectiveness. A similar growth-rate control is observed in pathogens that infect and persist inside their hosts. The bacterial toxin-antitoxin (TA) system serves as a non-heritable phenotypic switch by slowing down growth through the expression of a toxin component. Here, we investigated a HigB-like type II toxin from the intracellular bacterial pathogen Salmonella Typhimurium. Unlike other HigB-like toxins that cleave ribosome-bound mRNAs, it does not exhibit endoribonuclease activity. Instead, it inhibits ribonuclease III, which mediates the initial cleavage for rRNA processing, by directly binding to the dsRNA-binding domain of RNase III, thereby decreasing ribosome assembly and bacterial growth. Given that the formation of HigB-like toxin-mediated non-replicating Salmonella within macrophages is RNase III-dependent, persister formation by inhibiting RNase III is a newly identified strategy for pathogens to survive within host cells.