Escherichia coli mechanisms of copper homeostasis in a changing environment.

Escherichia coli is equipped with multiple systems to ensure safe copper handling under varying environmental conditions. The Cu(I)-translocating P-type ATPase CopA, the central component in copper homeostasis, is responsible for removing excess Cu(I) from the cytoplasm. The multi-copper oxidase CueO and the multi-component copper transport system CusCFBA appear to safeguard the periplasmic space from copper-induced toxicity. Some strains of E. coli can survive in copper-rich environments that would normally overwhelm the chromosomally encoded copper homeostatic systems. Such strains possess additional plasmid-encoded genes that confer copper resistance. The pco determinant encodes genes that detoxify copper in the periplasm, although the mechanism is still unknown. Genes involved in copper homeostasis are regulated by MerR-like activators responsive to cytoplasmic Cu(I) or two-component systems sensing periplasmic Cu(I). Pathways of copper uptake and intracellular copper handling are still not identified in E. coli.