Characterization of a novel two-partner secretion system implicated in the virulence of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen implicated in nosocomial infection and infecting people with compromised immune systems such as cystic fibrosis patients. Although multiple genes involved in P. aeruginosa pathogenesis have been characterized, the overall mechanism of virulence is not fully understood. In this study, we identified a functional two-partner secretion (TPS) system, composed of the PdtA exoprotein and its cognate pore-forming β-barrel PdtB transporter, which is implicated in the virulence of P. aeruginosa. We found that the predicted PdtA exoprotein is related to the HMW-like adhesins subfamily TPS systems. We demonstrate here that limitation of inorganic phosphate (Pi) allows the production of PdtA protein. We show that PdtA is processed during its outer-membrane translocation, with an N-terminal domain released into the extracellular environment and a C-terminal domain associated with the outer membrane of the cell. We also obtained evidence that the transport of PdtA is strictly dependent on the production of PdtB, a result confirming that these proteins constitute a functional TPS system. Furthermore, using the Caenorhabditis elegans model of infection, we show that a pdtA mutant is less virulent than the wild-type strain.