title: Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms.
abstract: The prevalent formation of noncrystalline U(IV) species in the subsurface and their enhanced susceptibility to reoxidation and remobilization, as compared to crystalline uraninite, raise concerns about the long-term sustainability of the bioremediation of U-contaminated sites. The main goal of this study was to resolve the remaining uncertainty concerning the formation mechanism of noncrystalline U(IV) in the environment. Controlled laboratory biofilm systems (biotic, abiotic, and mixed biotic-abiotic) were probed using a combination of U isotope fractionation and X-ray absorption spectroscopy (XAS). Regardless of the mechanism of U reduction, the presence of a biofilm resulted in the formation of noncrystalline U(IV). Our results also show that biotic U reduction is the most effective way to immobilize and reduce U. However, the mixed biotic-abiotic system resembled more closely an abiotic system: (i) the U(IV) solid phase lacked a typically biotic isotope signature and (ii) elemental sulfur was detected, which indicates the oxidation of sulfide coupled to U(VI) reduction. The predominance of abiotic U reduction in our systems is due to the lack of available aqueous U(VI) species for direct enzymatic reduction. In contrast, in cases where bicarbonate is present at a higher concentration, aqueous U(VI) species dominate, allowing biotic U reduction to outcompete the abiotic processes.
authors.affiliation: Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Stylo
authors.affiliation: Institut für Mineralogie, Leibniz Universitat Hannover , D-30167 Hannover, Germany.
authors.forename: Nadja
authors.initials: N
authors.lastname: Neubert
authors.affiliation: Institut für Mineralogie, Leibniz Universitat Hannover , D-30167 Hannover, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Roebbert
authors.affiliation: Institut für Mineralogie, Leibniz Universitat Hannover , D-30167 Hannover, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weyer
authors.affiliation: Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmani
mesh_terms: D001673:Biodegradation, Environmental; D018441:Biofilms; D016969:Desulfovibrio vulgaris / Q000378:metabolism*; D007501:Iron / Q000032:analysis; D010084:Oxidation-Reduction; D013440:Sulfides / Q000032:analysis; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D013440:Sulfides; D014501:Uranium; D007501:Iron