Comparative study on Ni(2+)-affinity transport of nickel/cobalt permeases (NiCoTs) and the potential of recombinant Escherichia coli for Ni(2+) bioaccumulation.

Comparative evaluation on Ni(2+)-uptake of two nickel-affinity transmembrane proteins (NiCoTs) respectively from Helocobacter pylori (NixA) and Staphylococcus aureus (NisA) was performed. Expression of NiCoTs alone did not promote Ni(2+) uptake of the recombinant strains and made the growth susceptible to Ni(2+). However, recombinant strains expressing both NiCoTs and Metallothionein (MT) showed enhanced tolerance to Ni(2+) and Ni(2+) uptake. The maximum Ni(2+)-uptake capacity of recombinant strain N1c expressing NixA+MT reached 83.33mgg(-1), higher than 45.45mgg(-1) of recombinant strain N1d expressing NisA+MT. N1c exhibited more effective Ni(2+) accumulation than N1d in the presence of Na(+), Co(2+) and Cd(2+). NiCoTs promoted intracellular Ni(2+) uptake of the recombinant strains. Phosphate groups dominated Ni(2+) binding of wild type Escherichia coli, but carboxyl groups contributed more for N1c and N1d. The result suggested that NixA has a higher specificity in Ni(2+) binding than NisA, and both NiCoTs and MT are important for Ni(2+) bioaccumulation.