An ADP-ribosyltransferase toxin kills bacterial cells by modifying structured non-coding RNAs

ADP-ribosyltransferases (ARTs) were among the first identified bacterial virulence factors. Canonical ART toxins are delivered into host cells where they modify essential proteins, thereby inactivating cellular pro-cesses and promoting pathogenesis. Our understanding of ARTs has since expanded beyond protein -target-ing toxins to include antibiotic inactivation and DNA damage repair. Here, we report the discovery of RhsP2 as an ART toxin delivered between competing bacteria by a type VI secretion system of Pseudomonas aer-uginosa. A structure of RhsP2 reveals that it resembles protein-targeting ARTs such as diphtheria toxin. Remarkably, however, RhsP2 ADP-ribosylates 20-hydroxyl groups of double-stranded RNA, and thus, its ac-tivity is highly promiscuous with identified cellular targets including the tRNA pool and the RNA-processing ribozyme, ribonuclease P. Consequently, cell death arises from the inhibition of translation and disruption of tRNA processing. Overall, our data demonstrate a previously undescribed mechanism of bacterial antago-nism and uncover an unprecedented activity catalyzed by ART enzymes.

Automated summary

ADP-ribosyltransferases (ARTs) are bacterial virulence factors that modify essential proteins to promote pathogenesis. This study reports the discovery of RhsP2 as an ART toxin delivered by a type VI secretion system. RhsP2 can ADP-ribosylate double-stranded RNA, leading to inhibition of translation and disruption of tRNA processing, ultimately causing cell death. This finding uncovers a previously unknown mechanism of bacterial antagonism and highlights the unprecedented activity of ART enzymes.