Abstract
The PhoPQ two-component regulatory system coordinates the response of Salmonella enterica serovar Typhimurium to diverse environmental challenges encountered during infection of hosts, including changes in Mg2+ concentrations, pH, and antimicrobial peptides. Moreover, PhoPQ-dependent regulation of gene expression promotes intracellular survival of Salmonella in macrophages, and contributes to the resistance of this pathogen to reactive nitrogen species (RNS) generated from the nitric oxide produced by the inducible nitric oxide (NO) synthase of macrophages. We report here that Salmonella strains with mutations of phoPQ are hypersensitive to killing by RNS generated in vitro. The increased susceptibility of ∆phoQ Salmonella to RNS requires molecular O2 and coincides with the nitrotyrosine formation, the oxidation of [4Fe-4S] clusters of dehydratases, and DNA damage. Mutations of respiratory NADH dehydrogenases prevent nitrotyrosine formation and abrogate the cytotoxicity of RNS against ∆phoQ Salmonella, presumably by limiting the formation of peroxynitrite (ONOO−) arising from the diffusion-limited reaction of exogenous NO and endogenous superoxide (O2•−) produced in the electron transport chain. The mechanism underlying PhoPQ-mediated resistance to RNS is linked to the coordination of Mg2+ homeostasis through the PhoPQ-regulated MgtA transporter. Collectively, our investigations are consistent with a model in which PhoPQ-dependent Mg2+ homeostasis protects Salmonella against nitrooxidative stress.
Highlights
Mutations in phoPQ attenuate Salmonella virulence by at least 10,000-fold[1,2,3]
To learn more about the role of PhoPQ in resistance of Salmonella to reactive nitrogen species (RNS), we investigated the survival of a ∆phoQ mutant exposed to the nitric oxide (NO) generator spermine NONOate
A dose-dependent inhibition of growth by spermine NONOate (sperNO) was observed for both ∆phoP or ∆phoQ strains when inoculated in LB broth or minimal E salts medium supplemented with malic acid (Fig. 1C and Fig. S1), which is consistent with the notion that the PhoP response regulator boosts the antinitrosative potential of Salmonella in conjunction with its cognate PhoQ sensor kinase
Summary
The attenuated phenotype of phoPQ mutants has been associated with poor intracellular survival in macrophages, defective activation of Salmonella pathogenicity island 2 (SPI2) transcription, and hypersensitivity to defensins, antimicrobial peptides, divalent cations, iron, acid and bile salts[1,4,5,6,7,8,9,10]. The low NO fluxes generated in the innate response dramatically limit the synthesis of autooxidative products such as dinitrogen trioxide (N2O3), which has been associated with sustained anti-Salmonella activity of IFNγ-primed macrophages[17]. We have recently shown that PhoPQ signaling enhances the intracellular fitness of Salmonella by antagonizing the innate host response associated with NO13. System enhances the resistance of Salmonella against the nitrooxidative stress generated in the interaction of exogenous NO with endogenously produced O2− through its regulation of intracellular Mg2+ concentrations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
