Discovery of a Pseudomonas aeruginosa Type VI secretion system toxin targeting bacterial protein synthesis using a global genomics approach

The Type VI secretion system (T6SS) is a bacterial weapon which delivers toxic effectors to kill competitors or subvert some of their key functions. Here we use transposon directed insertion-site sequencing (TraDIS) to identify T6SS toxins associated with the H1-T6SS, one of the three T6SS machines found in Pseudomonas aeruginosa. This approach identified several putative toxin-immunity pairs, including Tse8-Tsi8. Full characterization of this protein pair demonstrated that Tse8 is delivered by the VgrG1a spike complex into prey cells where it targets the transamidosome, a multiprotein complex involved in protein synthesis in bacteria lacking either one or both of the asparagine or glutamine tRNA synthases. Our data suggests that Tse8 combines as a non-cognate component of the transamidosome complex, reducing fitness by limiting the ability of the cell to synthesize proteins. This is the first demonstration of a T6SS toxin affecting protein synthesis, expanding the range of cellular components targeted by this bacterial weapon. The success of the current study validates the use of our TraDIS approach as a tool to drastically expand the repertoire of T6SS toxins in any T6SS-encoding bacterium.