COMPARATIVE ANALYSIS OF CUEP AND CUS FOR SALMONELLA PERIPLASMIC COPPER HOMEOSTASIS AND VIRULENCE

LÓPEZ, CAROLINA; GIRI, GERMÁN F.; PEZZA, ALEJANDRO; PONTEL, LUCAS BLAS; SONCINI, FERNANDO C.

Potsdam

Conferencia; 5th ASM Conference on Salmonella; 2016

American Society for Microbiology

Copper is an essential ion that participates in enzymatic reactions carried out by bacterial periplasmic cuproproteins such as cytochrome oxidases, NADH dehydrogenases, Cu, Zn­ superoxide dismutases, laccases and multicopper oxidases, among others. It is, at the same time, extremely reactive causing damage to proteins, lipids and other cellular components. Most enterobacterial species harbor a copper­ responsive two­ component system, CusR/CusS, to control the ion levels in the cell envelope. CusR/CusS responds to the surplus of periplasmic copper inducing the expression of the CBA­type efflux complex CusC(F)BA that pumps out of the cell the excess of the metal ion. Most Salmonella serotypes lack both the genes coding for CusR/CusS and the operon encoding the CusC(F)BA efflux complex, and different lines of evidence suggest that envelope protection against copper overload depends on CueP, a major copper ­binding protein in the periplasm required for macrophage survival and virulence. The Salmonella ­specific CueP­ coding gene was originally identified as part of the Cue regulon under the transcriptional control of the cytoplasmic copper sensor CueR, but itsexpression differs from the rest of CueR­ regulated genes. We now show that cueP expression is controlled by the concerted action of CueR, which detects the presence of copper in the cytoplasm, and by CpxR/CpxA that monitors envelope stress. The integration of two ancestral sensory systems ­CueR, which provides a signal specificity, and CpxR/CpxA that detects stress in the bacterial envelope­ restricts the expression of this periplasmic copper resistance protein only to cells encountering surplus copper that disturbs envelope homeostasis, emulating the role of the CusR/CusS regulatory system present in other enteric bacteria.Furthermore, we show that coordinated regulation of cueP by CueR and CpxR/CpxA is required for optimal growth. CueP . expression from a CpxR­ independent promoter impairs growth during exponential phase. In addition, this strain shows a marked growth defect in presence of H2O2. Finally, a strain with the Escherichia coli cus locus in place of cueP showed displayed wild ­type resistance to the metal ion but showed a deficiency was unable to survive in macrophage survival, suggesting that cueP acquisition by Salmonella was necessary to establish its intracellular lifestyle