title: U(VI) reduction to mononuclear U(IV) by Desulfitobacterium species.
abstract: The bioreduction of U(VI) to U(IV) affects uranium mobility and fate in contaminated subsurface environments and is best understood in Gram-negative model organisms such as Geobacter and Shewanella spp. This study demonstrates that U(VI) reduction is a common trait of Gram-positive Desulfitobacterium spp. Five different Desulfitobacterium isolates reduced 100 microM U(VI) to U(IV) in <10 days, whereas U(VI) remained soluble in abiotic and heat-killed controls. U(VI) reduction in live cultures was confirmed using X-ray absorption near-edge structure (XANES) analysis. Interestingly, although bioreduction of U(VI) is almost always reported to yield the uraninite mineral (UO(2)), extended X-ray absorption fine structure (EXAFS) analysis demonstrated that the U(IV) produced in the Desulfitobacterium cultures was not UO(2). The EXAFS data indicated that the U(IV) product was a phase or mineral composed of mononuclear U(IV) atoms closely surrounded by light element shells. This atomic arrangement likely results from inner-sphere bonds between U(IV) and C/N/O- or P/S-containing ligands, such as carbonate or phosphate. The formation of a distinct U(IV) phase warrants further study because the characteristics of the reduced material affect uranium stability and fate in the contaminated subsurface.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332, USA.
authors.forename: Kelly E
authors.initials: KE
authors.lastname: Fletcher
authors.forename: Maxim I
authors.initials: MI
authors.lastname: Boyanov
authors.forename: Sara H
authors.initials: SH
authors.lastname: Thomas
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Wu
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Kemner
authors.forename: Frank E
authors.initials: FE
authors.lastname: Löffler
mesh_terms: D001673:Biodegradation, Environmental; D045858:Desulfitobacterium / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D012995:Solubility; D014501:Uranium / Q000302:isolation & purification*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D014501:Uranium