Bio-precipitation of uranium by two bacterial isolates recovered from extreme environments as estimated by potentiometric titration, TEM and X-ray absorption spectroscopic analyses

• Published in: Journal of hazardous materials Vol. 197; pp. 1 - 10
• Main Authors: Merroun, Mohamed L., Nedelkova, Marta, Ojeda, Jesus J., Reitz, Thomas, Fernández, Margarita López, Arias, José M., Romero-González, María, Selenska-Pobell, Sonja
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-12-2011; Elsevier
• Subjects: absorption; Acid phosphatase; Applied sciences; Bacillus - classification; Bacillus - metabolism; Bacillus sphaericus; Bacteria; Biodegradation, Environmental; Biomineralization; cell walls; Exact sciences and technology; ions; Microscopy, Electron, Transmission - methods; Phosphates; Phylogeny; Pollution; Potentiometric titration; Potentiometry - methods; Precipitates; Precipitation; Sphingomonas; Sphingomonas - classification; Sphingomonas - metabolism; TEM/EDX; titration; Transmission electron microscopy; Uranium; Uranium - metabolism; Uranium biomineralization; X-radiation; X-ray absorption spectroscopy; X-Ray Absorption Spectroscopy - methods; XAS; XAS; TEM/EDX; Acid phosphatase; Uranium biomineralization; Potentiometric titration; Radioactive pollution; Pollutant behavior; Ligand; Radioisotope; Cell wall; X ray absorption spectrometry; Transmission electron microscopy; Uranium; Organic phosphate; pH; Speciation; X ray absorption
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.09.049

► Precipitation of uranium as U phosphates by natural bacterial isolates. ► The uranium biomineralization involves the activity of acidic phosphatase. ► Uranium bioremediation could be achieved via the biomineralization of U(VI) in phosphate minerals.
This work describes the mechanisms of uranium biomineralization at acidic conditions by Bacillus sphaericus JG-7B and Sphingomonas sp. S15-S1 both recovered from extreme environments. The U–bacterial interaction experiments were performed at low pH values (2.0–4.5) where the uranium aqueous speciation is dominated by highly mobile uranyl ions. X-ray absorption spectroscopy (XAS) showed that the cells of the studied strains precipitated uranium at pH 3.0 and 4.5 as a uranium phosphate mineral phase belonging to the meta-autunite group. Transmission electron microscopic (TEM) analyses showed strain-specific localization of the uranium precipitates. In the case of B. sphaericus JG-7B, the U(VI) precipitate was bound to the cell wall. Whereas for Sphingomonas sp. S15-S1, the U(VI) precipitates were observed both on the cell surface and intracellularly. The observed U(VI) biomineralization was associated with the activity of indigenous acid phosphatase detected at these pH values in the absence of an organic phosphate substrate. The biomineralization of uranium was not observed at pH 2.0, and U(VI) formed complexes with organophosphate ligands from the cells. This study increases the number of bacterial strains that have been demonstrated to precipitate uranium phosphates at acidic conditions via the activity of acid phosphatase.