Transcriptional control of copper-resistance in Salmonella

PEZZA, A.; PONTEL, L. B.; SONCINI, F. C.

4th ASM Conference on Salmonella: The Bacterium, the Host and the Environment

Conferencia; 4th ASM Conference on Salmonella: The Bacterium, the Host and the Environment; 2013

American Society for Microbiology

Copper (Cu) is an essential metal required as cofactor in numerous essential biochemical reactions and at the same time highly toxic. Cu toxicity is handled by the cue regulon in most Gram(-) bacteria that includes the Cu-sensor/regulator CueR responsible for the transcriptional control of genes coding for the Cu-efflux pump CopA and the periplasmic multicopper oxidase CueO. Under anaerobic conditions most species also require the Cus system to cope with Cu excess. This includes CusR/CusS, a two-component system that senses periplasmic Cu and induces the expression of CusCFBA, an RND-based Cu-efflux pump that eliminates the excess of the metal ion from the periplasm. In Salmonella as well as in other species that do not harbor the cus locus there is a periplasmic protein encoded by a CueR-regulated gene, cueP. We have previously demonstrated that the homeostasis of Cu in the periplasm relies on CueP and that CueP can functionally substitute the Cus complex, in particular under anaerobic conditions. Recent observations suggest that under Cu limitation CueP is required for the supply of the metal ion to SodCII, one of the periplasmic Cu/Zn-SODs. However, these observations do not explain the induction of CueP in the presence of excess of the metal ion, and its role in Cu-resistance. In this work, we examined the transcriptional regulation of the Salmonella cue regulon in different environments. We observed a differential expression within its constituents that affect in particular the expression of cueP. By the combination of bioinformatics and site-directed mutagenesis we detected a putative cis-acting sequence within the promoter of cueP responsible for this differential expression. In vivo transcription as well as DNA-footprinting experiments allowed us to confirm the existence of this regulatory element, sensitive to the periplasmic stress caused by Cu excess. Phenotypic analysis allowed us to demonstrate that this periplasmic-stress sensory element acts in concert with CueR to ensure the correct supply of this component of the cue regulon when the environment becomes unfavorable for survival.