Alternative periplasmic copper resistance mechanisms in Gram negative bacteria

LUCAS B. PONTEL; FERNANDO C. SONCINI

MOLECULAR MICROBIOLOGY

Blackwell Publishing Ltd.

Año: 2009 vol. 79 p. 212 - 225

0950-382X

Bacteria have evolved different systems to tightly control both cytosolic and envelope copper concentration to fulfil their requirements and at the same time, avoid copper toxicity. We have previously demonstrated that, as in E. coli, the Salmonella cue system protects the cytosol from copper excess. On the other hand, and even though Salmonella lacks the CusCFBA periplasmic copper efflux system, it can support higher copper concentrations than E. coli under anaerobic conditions. Here we show that the Salmonella cue regulon is also responsible for the control of copper toxicity in anaerobiosis. We establish that resistance in this condition requires a novel CueR-controlled gene named cueP. A ÄcueP mutant is highly susceptible to copper in the absence of oxygen, but shows a faint phenotype in aerobic conditions unless other copper-resistance genes are also deleted, resembling the E. coli CusCFBA behavior. Species that contain a cueP-homolog under CueR-regulation have no functional CusR/CusS-dependent Cus coding operon. Conversely, species that carry a CusR/CusS-regulated cus operon have no cueP-homologues. Even more, we show that the CueR-controlled cueP expression increases copper resistance of a Äcus E. coli. We posit that CueP can functionally replace the Cus complex for periplasmic copper resistance, in particular under anaerobic conditions.