Expression of a plasmid-encoded gene for cadmium resistance of Pseudomonas putida GAM-1 in Escherichia coli

A Cd²⁺-resistant Escherichia coli C600 transformant harboring pGU100, which was derived from Cd²⁺-resistant Pseudomonas putida GAM-1, was able to grow in concentrations of CdCl₂ as high as 3.5 mM, whereas E. coli C600 could not grow in the presence of 1.5 mM CdCl₂. E. coli C600 (pGU100) possesses a Cd²⁺ efflux system. This efflux system was inhibited by 100 μM dicyclohexylcarbodiimide, indicating that the system seems to be energy-dependent. Further studies revealed that the Cd²⁺ efflux system of E. coli C600 (pGU100) can operate under proliferous conditions, but not under nonproliferous conditions.