Reduction of U(VI) in goethite (α-FeOOH) suspensions by a dissimilatory metal-reducing bacterium

Abstract

Dissimilatory metal-reducing bacteria (DMRB) can utilize Fe(III) associated with aqueous complexes or solid phases, such as oxide and oxyhydroxide minerals, as a terminal electron acceptor coupled to the oxidation of H 2 or organic substrates. These bacteria are also capable of reducing other metal ions including Mn(IV), Cr(VI), and U(VI), a process that has a pronounced effect on their solubility and overall geochemical behavior. In spite of considerable study on an individual basis, the biogeochemical behavior of multiple metals subject to microbial reduction is poorly understood. To probe these complex processes, the reduction of U(VI) by the subsurface bacterium, Shewanella putrefaciens CN32, was investigated in the presence of goethite under conditions where the aqueous composition was controlled to vary U speciation and solubility. Uranium(VI), as the carbonate complexes UO 2 (CO 3) 3(aq) 4Ϫ and UO 2 (CO 3) 2(aq) 2Ϫ , was reduced by the bacteria to U(IV) with or without goethite [␣-FeOOH (s) ] present. Uranium(VI) in 1,4-piperazinediethhanesulfonic acid (PIPES) buffer that was estimated to be present predominantly as the U(VI) mineral metaschoepite [UO 3 ⅐ 2H 2 O (s) ], was also reduced by the bacteria with or without goethite. In contrast, only ϳ30% of the U(VI) associated with a synthetic metaschoepite was reduced by the organism in the presence of goethite with 1 mM lactate as the electron donor. This may have been due to the formation of a layer of UO 2(s) or Fe(OH) 3(s) on the surface of the metaschoepite that physically obstructed further bioreduction. Increasing the lactate to a non-limiting concentration (10 mM) increased the reduction of U(VI) from metaschoepite to greater than 80% indicating that the hypothesized surface-veneering effect was electron donor dependent. Uranium(VI) was also reduced by bacterially reduced anthraquinone-2,6-disulfonate (AQDS) in the absence of cells, and by Fe(II) sorbed to goethite in abiotic control experiments. In the absence of goethite, uraninite was a major product of direct microbial reduction and reduction by AH 2 DS. These results indicate that DMRB, via a combination of direct enzymatic or indirect mechanisms, can reduce U(VI) to insoluble U(IV) in the presence of solid Fe oxides.

Effect of biogeochemical redox processes on the fate and transport of As and U at an abandoned uranium mine site: an X-ray absorption spectroscopy study

“…Sediment sulfur concentrations (measured by Larson et al [4] ) and sediment Fe concentrations in the pond could allow for the precipitation of amorphous FeS, following microbial reduction of sulfate and Fe III oxy(hydr)oxides, which can abiotically reduce uranyl to uraninite or non-uraninite U IV . [4,13,15,27,65] Because of the low environmental sediment U concentrations, U XANES spectra were only obtained for the top of the tailings, toe of the tailings, pond and pond outlet (Figs S7, S8, Table S2 of the Supplementary material). Of the collected spectra, the U XANES spectrum from the pond outlet was fit with the greatest percentage of U IV (45.1 %).…”

Structural Similarities between Biogenic Uraninites Produced by Phylogenetically and Metabolically Diverse Bacteria

“…If these results are found to transcend delta-and gamma-proteobacteria, then field-relevant variables such as uranium concentration, groundwater composition, biologically enhanced adsorption-driven reactions, and the potential for redox cycling by iron oxide phases such as green rust, goethite, reduced quinones, or humics (13,22,37) could play a more important role.…”

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

“…Research thus far has demonstrated U(VI) reduction by Fe(II) sorbed onto a variety of iron oxides/oxyhydroxides (Charlet et al, 1998;Liger et al, 1999;Fredrickson et al, 2000;Jeon et al, 2004), Fe(II)-containing natural sediments (Behrends and Van Cappellen, 2005;Jeon et al, 2005), Fe(II)-containing carboxyl-functionalized microspheres (Boyanov et al, 2007), Fe(II) sorbed on corundum (Regenspurg et al, 2009) and Fe(II) sorbed on montmorillonite (Chakraborty et al, 2010). These studies primarily consider surface catalyzed processes that involved either concomitant or sequential adsorption of aqueous Fe(II) and U(VI) species onto a solid phase adsorbent or mineral to mediate abiotic U(VI) reduction.…”