Nickel resistance in Escherichia coli V38 is dependent on the concentration used for induction

Strain Escherichia coli V38 resistant to 4 mM NiCl2 was isolated from the city sewage sludge. It showed low nickel accumulation by cells and nickel ion efflux. Cells were pregrown (induced) overnight in the presence of Ni2+, then the culture was kept on ice for 20-30 min and transferred to 37 degrees C for further incubation. When the Ni2+ concentration during growth was the same as during incubation, there was no noticeable accumulation of Ni2+. When the Ni2+ concentration during incubation was higher than that used for induction, uptake of 63Ni2+ and delayed efflux were seen. The uptake and delay of both efflux and growth were directly proportional to the difference between the concentrations used for induction and incubation. Active nickel ion uptake was seen in cells taken from cultures in the delayed efflux period.