Inorganic Polyphosphate Is Essential for Salmonella Typhimurium Virulence and Survival in Dictyostelium discoideum

Macarena A. Varas, Sebastián Riquelme-Barrios, Camila Valenzuela, Andrés E. Marcoleta, Camilo Berríos-Pastén, Carlos A. Santiviago, Francisco P. Chávez

Inorganic polyphosphate (polyP) deficiency in enteric bacterial pathogens reduces their ability to invade and establish systemic infections in different hosts. For instance, inactivation of the polyP kinase gene (ppk) encoding the enzyme responsible for polyP biosynthesis reduces invasiveness and intracellular survival ofSalmonella entericaserovar Typhimurium (S. Typhimurium) in epithelial cells and macrophagesin vitro. In addition, the virulencein vivoof aS. Typhimurium Δppkmutant is significantly reduced in a murine infection model. In spite of these observations, the role played by polyP during theSalmonella-host interaction is not well understood. The social amoebaDictyostelium discoideumhas proven to be a useful model for studying relevant aspects of the host-pathogen interaction. In fact, many intracellular pathogens can survive withinD. discoideumcells using molecular mechanisms also required to survive within macrophages. Recently, we established thatS. Typhimurium is able to survive intracellularly inD. discoideumand identified relevant genes linked to virulence that are crucial for this process. The aim of this study was to determine the effect of a polyP deficiency inS. Typhimurium during its interaction withD. discoideum. To do this, we evaluated the intracellular survival of wild-type and Δppkstrains ofS. Typhimurium inD. discoideumand the ability of these strains to delay the social development of the amoeba. In contrast to the wild-type strain, the Δppkmutant was unable to survive intracellularly inD. discoideumand enabled the social development of the amoeba. Both phenotypes were complemented using a plasmid carrying a copy of theppkgene. Next, we simultaneously evaluated the proteomic response of bothS. Typhimurium andD. discoideumduring host-pathogen interaction via global proteomic profiling. The analysis of our results allowed the identification of novel molecular signatures that give insight intoSalmonella-Dictyosteliuminteraction. Altogether, our results indicate that inorganic polyP is essential forS. Typhimurium virulence and survival inD. discoideum. In addition, we have validated the use of global proteomic analyses to simultaneously evaluate the host-pathogen interaction ofS. Typhimurium andD. discoideum. Furthermore, our infection assays using these organisms can be exploited to screen for novel anti-virulence molecules targeting inorganic polyP biosynthesis.