Vanadium-binding protein excreted by vanadate-reducing bacteria

A vanadium-binding protein was isolated from the culture medium of the vana dium-reducing bacterium Pseudomonas isachenkovii by utilizing vanadate as t he terminal electron acceptor upon anaerobic respiration. The protein was a ssociated with vanadium at a molar ratio of similar to 1:20. It was purifie d to homogeneity and separated into three components by treatment with 1 M HCl followed by gel filtration: a protein, a vanadium-binding ligand, and i norganic vanadium, Electron paramagnetic resonance analysis showed that van adium was associated with the protein in the 4+ oxidation state, The distri bution of vanadium within the cell was studied by electron microscopy and x -ray microanalysis of P. isachenkovii cells. The results suggest that vanad ium, accumulated in special swells on the surface of the cell membranes, is reduced and excreted to the medium.