Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20.
This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 μm filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.
Department of Civil and Environmental Engineering, Southern Methodist University, Dallas, TX, 75275-0339, USA.
S Sevinç
SS
Şengör
Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, 501 East St. Joseph Street, Rapid City, SD, 57701-3995, USA.
Gursharan
G
Singh
WR Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
Alice
A
Dohnalkova
Lawrence Berkeley National Laboratory, Earth Sciences Division, 1 Cyclotron Rd, Berkeley, CA, 94720, USA.
Nicolas
N
Spycher
Department of Civil and Environmental Engineering, Washington State University, 405 Spokane Street, Pullman, WA, 99164, USA.
Timothy R
TR
Ginn
Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT, 59715, USA.
Brent M
BM
Peyton
Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, 501 East St. Joseph Street, Rapid City, SD, 57701-3995, USA. Rajesh.Sani@sdsmt.edu.
Rajesh K
RK
Sani
D001639:Bicarbonates / Q000737:chemistry; D002021:Buffers; D003901:Desulfovibrio / Q000254:growth & development / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D014501:Uranium / Q000737:chemistry*
D001639:Bicarbonates; D002021:Buffers; D014501:Uranium
Biogenic uranium; Mobile uraninite; Nanoparticles; Sulfate reducing bacteria; Uranium aggregates