Characterization of uraninite nanoparticles produced by Shewanella oneidensis MR-1
The reduction of uranium(VI) by Shewanella oneidensis MR-1 was studied to examine the effects of bioreduction kinetics and background electrolyte on the physical properties and reactivity to re-oxidation of the biogenic uraninite, UO2(s). Bioreduction experiments were conducted with uranyl acetate as the electron acceptor and sodium lactate as the electron donor under resting cell conditions in a 30 mM NaHCO3 buffer, and in a PIPES-buffered artificial groundwater (PBAGW). MR-1 was cultured in batch mode in a defined minimal medium with a specified air-to-medium volume ratio such that electron acceptor (O2) limiting conditions were reached just when cells were harvested for subsequent experiments. The rate of U(VI) bioreduction was manipulated by varying the cell density and the incubation temperature (1.0 _ 108 cell ml_1 at 20 _C or 2.0 _ 108 cell ml_1 at 37 _C) to generate U(IV) solids at ‘‘fast” and ‘‘slow” rates in the two different buffers. The presence of Ca in PBAGW buffer altered U(VI) speciation and solubility, and significantly decreased U(VI) bioreduction kinetics. High resolution transmission electron microscopy was used to measure uraninite particle size distributions produced under the four different conditions. The most common primary particle size was 2.9–3.0 nm regardless of U(VI) bioreduction rate or background electrolyte. Extended X-ray absorption fine-structure spectroscopy was also used to estimate uraninite particle size and was consistent with TEM results. The reactivity of the biogenic uraninite products with dissolved oxygen was tested, and neither U(VI) bioreduction rate nor background electrolyte had any statistical effect on oxidation rates. With MR-1, uraninite particle size was not controlled by the bioreduction rate of U(VI) or the background electrolyte. These results for MR-1, where U(VI) bioreduction rate had no discernible effect on uraninite particle size or oxidation rate, contrast with our recent research with Shewanella putrefaciens CN32, where U(VI) bioreduction rate strongly influenced both uraninite particle size and oxidation rate. These two studies with Shewanella species can be viewed as consistent if one assumes that particle size controls oxidation rates, so the similar uraninite particle sizes produced by MR-1 regardless of U(VI) bioreduction rate would result in similar oxidation rates. Factors that might explain why U(VI) bioreduction rate was an important control on uraninite particle size for CN32 but not for MR-1 are discussed.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 947032
- Report Number(s):
- PNNL-SA-63840; 25408; KP1704020
- Journal Information:
- Geochimica et Cosmochimica Acta, 72(20):4901-4915, Journal Name: Geochimica et Cosmochimica Acta, 72(20):4901-4915 Journal Issue: 20 Vol. 72; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABSORPTION
ACETATES
BINDING ENERGY
DISSOLVED GASES
ELECTROLYTES
ELECTRONS
Environmental Molecular Sciences Laboratory
FINE STRUCTURE
INCUBATION
KINETICS
LACTATES
OXIDATION
OXYGEN
PARTICLE SIZE
PHYSICAL PROPERTIES
SODIUM
SOLUBILITY
SPECTROSCOPY
TRANSMISSION ELECTRON MICROSCOPY
URANINITES
VALENCE