Dual regulation of <i>cueP</i> by the CueR and Cpx systems enables <i>Salmonella</i> adaptation to copper and <i>N</i> -chlorotaurine

Abstract Salmonella enterica is a facultative intracellular pathogen capable of surviving within host cells, where it faces a sophisticated immune arsenal. Within the phagosomal compartment, the bacterium encounters significant stress from copper and reactive chlorine species like N-chlorotaurine (N-ChT) generated during the oxidative burst. We investigated the regulatory mechanisms enabling Salmonella to adapt to this dual copper/oxidative stress, specifically focusing on the regulation and function of CueP. This periplasmic protein was previously proposed to bind copper ions and to transfer them to the superoxide dismutase SodCII. Here, we demonstrated that copper specifically triggered the CueR pathway and that N-ChT activated the Cpx pathway, simultaneous exposure to both stresses resulting in maximum cueP expression levels. Moreover, CueP was shown to be important for copper resistance in the absence of the multicopper oxidase CueO and exhibits high thermostability in the presence of copper. Additionally, in a ΔcueO background, copper is sufficient to activate the Cpx pathway, ensuring robust cueP induction even without external oxidative signals. These findings establish a direct molecular link between a host antimicrobial agent (N-ChT) and the activation of the Cpx-CueP axis, revealing a new layer of bacterial adaptation to innate immunity. Moreover, they highlight an integrated response strategy contributing to bacterial adaptation to the dual copper/oxidative stress.