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Applied and Environmental Microbiology, November 2003, p. 6442-6446, Vol. 69, No. 11
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.11.6442-6446.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Bioaccumulation of Copper Ions by Escherichia coli Expressing Vanabin Genes from the Vanadium-Rich Ascidian Ascidia sydneiensis samea

Marine Biological Laboratory, Graduate School of Science, Hiroshima University, Hiroshima 722-0073, Japan

Received 23 June 2003/ Accepted 12 August 2003

The genes encoding two vanadium-binding proteins, vanabin1 and vanabin2, from a vanadium-rich ascidian, Ascidia sydneiensis samea, were recently identified and cloned (T. Ueki, T. Adachi, S. Kawano, M. Aoshima, N. Yamaguchi, K. Kanamori, and H. Michibata, Biochim. Biophys. Acta 1626:43-50, 2003). The vanabins were found to bind vanadium(IV), and an excess of copper(II) ions inhibited the binding of vanadium(IV) to the vanabins in vitro. In this study, we constructed Escherichia coli strains that expressed vanabin1 or vanabin2 fused to maltose-binding protein (MBP) in the periplasmic space. We found that both strains accumulated about twenty times more copper(II) ions than the control BL21 strain, while no significant accumulation of vanadium was observed. The strains expressing either MBP-vanabin1 or MBP-vanabin2 absorbed approximately 70% of the copper ions in the medium to which 10 µM copper (II) ions were initially added. The MBP-vanabin1 and MBP-vanabin2 protein expressed in the periplasm bound to copper ions at a copper:protein molar ratio of 8:1 and 5:1, respectively, but MBP did not bind to copper ions. These data showed that the metal-binding proteins vanabin1 and vanabin2 bound copper ions directly and enhanced the bioaccumulation of copper ions by E. coli.