Non-uraninite products of microbial U(VI) reduction.
A promising remediation approach to mitigate subsurface uranium contamination is the stimulation of indigenous bacteria to reduce mobile U(VI) to sparingly soluble U(IV). The product of microbial uranium reduction is often reported as the mineral uraninite. Here, we show that the end products of uranium reduction by several environmentally relevant bacteria (Gram-positive and Gram-negative) and their spores include a variety of U(IV) species other than uraninite. U(IV) products were prepared in chemically variable media and characterized using transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) to elucidate the factors favoring/inhibiting uraninite formation and to constrain molecular structure/composition of the non-uraninite reduction products. Molecular complexes of U(IV) were found to be bound to biomass, most likely through P-containing ligands. Minor U(IV)-orthophosphates such as ningyoite [CaU(PO(4))(2)], U(2)O(PO(4))(2), and U(2)(PO(4))(P(3)O(10)) were observed in addition to uraninite. Although factors controlling the predominance of these species are complex, the presence of various solutes was found to generally inhibit uraninite formation. These results suggest a new paradigm for U(IV) in the subsurface, i.e., that non-uraninite U(IV) products may be found more commonly than anticipated. These findings are relevant for bioremediation strategies and underscore the need for characterizing the stability of non-uraninite U(IV) species in natural settings.
Environmental Microbiology Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH 1015, Switzerland. rizlan.bernier-latmani@epfl.ch
Rizlan
R
Bernier-Latmani
Harish
H
Veeramani
Elena Dalla
ED
Vecchia
Pilar
P
Junier
Juan S
JS
Lezama-Pacheco
Elena I
EI
Suvorova
Jonathan O
JO
Sharp
Nicholas S
NS
Wigginton
John R
JR
Bargar
D001673:Biodegradation, Environmental; D046969:Clostridium acetobutylicum / Q000254:growth & development / Q000378:metabolism*; D045859:Desulfotomaculum / Q000254:growth & development / Q000378:metabolism*; D053768:Metal Nanoparticles / Q000737:chemistry / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D020592:Shewanella / Q000254:growth & development / Q000378:metabolism*; D012990:Soil Pollutants, Radioactive / Q000737:chemistry / Q000378:metabolism*; D017974:Uranium Compounds / Q000737:chemistry / Q000378:metabolism*; D056928:X-Ray Absorption Spectroscopy
D012990:Soil Pollutants, Radioactive; D017974:Uranium Compounds; C012597:uranium dioxide