Plutonium(IV) Reduction by the Metal-Reducing BacteriaGeobacter metallireducensGS15 andShewanella oneidensisMR1

Abstract

ABSTRACTThe 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 bacteriaGeobacter metallireducensGS15 andShewanella oneidensisMR1 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 containingS. oneidensis, but little or no Pu(III) production was observed in cultures containingG. 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 bothS. oneidensisandG. metallireducens. When soluble Pu(IV)(EDTA) was provided as the terminal electron acceptor, cell suspensions of bothS. oneidensisandG. metallireducensrapidly 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.