Ni2+-uptake in Pseudomonas putida strain S4: a possible role of Mg2+-uptake pump

Essential metal ion homeostasis is based on regulated uptake of metal ions, both during its scarcity and abundance. Pseudomonas putida strain S4, a multimetal resistant bacterium, was employed to investigate Ni(2+) entry into cells. It was observed that Mg(2+) regulates the entry of Ni(2+) and by this plays a protective role to minimize Ni(2+) toxicity in this strain. This protection was evident in both growth as well as viability. Intracellular accumulation of Ni(2+) varied in accordance with Mg(2+) concentrations in the medium. It was hypothesized that Ni(2+) enters the cell using a broad Mg(2+) pump, i.e. the CorA system, as the CorA inhibitor, i.e. Co(III) Hex, also inhibits Ni 2+ uptake. This led to the inference that Mg(2+)-based protection was basically due to competitive inhibition of Ni(2+) uptake. We also show that Zn(2+) can further regulate the entry of Ni(2+).