A Pseudomonas aeruginosa Type VI Secretion Phospholipase D Effector Targets Both Prokaryotic and Eukaryotic Cells

Widely found in animal and plant-associated proteobacteria, type VI secretion systems (T6SSs) are potentially capable of facilitating diverse interactions with eukaryotes and/ or other bacteria. Pseudomonas aeruginosa encodes three distinct T6SS haemolysin coregulated protein (Hcp) secretion islands (H1, H2, and H3-T6SS), each involved in different aspects of the bacterium's interaction with other organisms. Here we describe the characterization of a P. aeruginosa H3-T6SS-dependent phospholipase D effector, PldB, and its three tightly linked cognate immunity proteins. PldB targets the periplasmof prokaryotic cells and exerts an antibacterial activity. Surprisingly, PldB also facilitates intracellular invasion of host eukaryotic cells by activation of the PI3K/ Akt pathway, revealing it to be a transkingdom effector. Our findings imply a potentially widespread T6SS-mediated mechanism, which deploys a single phospholipase effector to influence both prokaryotic cells and eukaryotic hosts.