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Applied and Environmental Microbiology, September 2007, p. 5897-5903, Vol. 73, No. 18
0099-2240/07/$08.00+0     doi:10.1128/AEM.00747-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Plutonium(IV) Reduction by the Metal-Reducing Bacteria Geobacter metallireducens GS15 and Shewanella oneidensis MR1

Hakim Boukhalfa,^* Gary A. Icopini, Sean D. Reilly, and Mary P. Neu^*

Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

Received 3 April 2007/ Accepted 10 July 2007

The bacterial reduction of actinides has been suggested as a possible remedial strategy for actinide-contaminated environments, and the bacterial reduction of Pu(VI/V) has the potential to produce highly insoluble Pu(IV) solid phases. However, the behavior of plutonium with regard to bacterial reduction is more complex than for other actinides because it is possible for Pu(IV) to be further reduced to Pu(III), which is relatively more soluble than Pu(IV). This work investigates the ability of the metal-reducing bacteria Geobacter metallireducens GS15 and Shewanella oneidensis MR1 to enzymatically reduce freshly precipitated amorphous Pu(IV) (OH)₄ [Pu(IV)(OH)_4(am)] and soluble Pu(IV)(EDTA). In cell suspensions without added complexing ligands, minor Pu(III) production was observed in cultures containing S. oneidensis, but little or no Pu(III) production was observed in cultures containing G. metallireducens. In the presence of EDTA, most of the Pu(IV)(OH)_4(am) present was reduced to Pu(III) and remained soluble in cell suspensions of both S. oneidensis and G. metallireducens. When soluble Pu(IV)(EDTA) was provided as the terminal electron acceptor, cell suspensions of both S. oneidensis and G. metallireducens rapidly reduced Pu(IV)(EDTA) to Pu(III)(EDTA) with nearly complete reduction within 20 to 40 min, depending on the initial concentration. Neither bacterium was able to use Pu(IV) (in any of the forms used) as a terminal electron acceptor to support growth. These results have significant implications for the potential remediation of plutonium and suggest that strongly reducing environments where complexing ligands are present may produce soluble forms of reduced Pu species.

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* Corresponding author. Mailing address: Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545. Phone: (505) 667-7219. Fax: (505) 606-2258. E-mail for Mary P. Neu: mneu{at}lanl.gov. E-mail for Hakim Boukhalfa: hakim{at}lanl.gov

Published ahead of print on 20 July 2007.

Present address: Montana Bureau of Mines and Geology, Butte, MT 59701.

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Applied and Environmental Microbiology, September 2007, p. 5897-5903, Vol. 73, No. 18
0099-2240/07/$08.00+0     doi:10.1128/AEM.00747-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Icopini, G. A., Lack, J. G., Hersman, L. E., Neu, M. P., Boukhalfa, H. (2009). Plutonium(V/VI) Reduction by the Metal-Reducing Bacteria Geobacter metallireducens GS-15 and Shewanella oneidensis MR-1. Appl. Environ. Microbiol. 75: 3641-3647 [Abstract] [Full Text]