The YjfJ protein is the effector of a second PspA/VIPP1 system that is widespread in the Gammaproteobacteria

Maintaining the integrity of the cytoplasmic membrane is essential for bacterial cell survival. Unsurprisingly, prokaryotes have evolved conserved mechanisms by which they sense, maintain, and repair membrane integrity in response to stress. The phage shock protein (Psp) is one such system, understood primarily through work undertaken in the Gammaproteobacterial species Escherichia coli and Yersinia enterocolitica. The system utilises an effector, PspA, alongside accessory proteins that sense stress and recruit PspA to damaged membranes. Homologues of PspA - part of the PspA/VIPP1 family - are found in a variety of bacterial phyla. Although most work in the Gammaproteobacteria has concerned the canonical Psp response, there have been descriptions of non-canonical PspA/VIPP1-containing systems that warrant further genomic analysis. By analysing the PspA/VIPP1 content of a diverse selection of Gammaproteobacterial genomes, we reveal the existence of two phylogenetically distinct subtypes of PspA/VIPP1 proteins, PspA- and YjfJ-like, which are found at similar frequencies. The YjfJ-like proteins are not only a novel subtype of PspA/VIPP1, having their own unique set of accessory proteins, but in some species, such as the ESKAPE pathogen Pseudomonas aeruginosa, comprise the only PspA/VIPP1-containing system. Our study positions the YjfJ-like containing systems on equal footing with the PspA system in terms of their conservation and distribution in the Gammaproteobacteria. This suggests that studies into the biological functions of YjfJ-like proteins would be well-justified from their unique presence in some important human pathogens.