Plutonium(V/VI) Reduction by the Metal-Reducing BacteriaGeobacter metallireducensGS-15 andShewanella oneidensisMR-1

Abstract

ABSTRACTWe examined the ability of the metal-reducing bacteriaGeobacter metallireducensGS-15 andShewanella oneidensisMR-1 to reduce Pu(VI) and Pu(V). Cell suspensions of both bacteria reduced oxidized Pu [a mixture of Pu(VI) and Pu(V)] to Pu(IV). The rate of plutonium reduction was similar to the rate of U(VI) reduction obtained under similar conditions for each bacteria. The rates of Pu(VI) and U(VI) reduction by cell suspensions ofS. oneidensiswere slightly higher than the rates observed withG. metallireducens. The reduced form of Pu was characterized as aggregates of nanoparticulates of Pu(IV). Transmission electron microscopy images of the solids obtained from the cultures after the reduction of Pu(VI) and Pu(V) byS. oneidensisshow that the Pu precipitates have a crystalline structure. The nanoparticulates of Pu(IV) were precipitated on the surface of or within the cell walls of the bacteria. The production of Pu(III) was not observed, which indicates that Pu(IV) was the stable form of reduced Pu under these experimental conditions. Experiments examining the ability of these bacteria to use Pu(VI) as a terminal electron acceptor for growth were inconclusive. A slight increase in cell density was observed for bothG. metallireducensandS. oneidensiswhen Pu(VI) was provided as the sole electron acceptor; however, Pu(VI) concentrations decreased similarly in both the experimental and control cultures.