EXAFS investigations of the uranium complexes formed by bacterial cells, S-layers and bioceramics

Microorganisms and their biocomponents affect the mobility and toxicity of radionuclides through solubility and speciation changes, biosorption, bioaccumulation or other bio-transformations. In this paper we report structural information on the uranium complexes formed by different bacterial isolates from uranium mining waste piles and by their purified biocomponents. EXAFS fits indicate that for B. sphaericus JG-A12 U(VI) is coordinated to carboxyl groups in a bidentate arrangement (RU-C= 2.91 ± 0.02 Å), and to phosphates in a mondentate fashion (RU-P = 3.59 ± 0.02 Å). For the other bacteria strains belonging to A. ferrooxidans, S. maltophilia, P. stutzeri, and P. migulae species U (VI) was bound only to phosphate (RU-P = 3.63 ± 0.02 Å). Because of the ability of the strain B. sphaericus JG A12 to bind selectively and reversibly U and other heavy metals, it was chosen for construction of so called biological ceramics (biorers) for bioremediation of metal-polluted waters. The sorption of U(VI) by the biocers occurs mainly via silicate and phosphate groups. The SiO2-matrix alone binds U (VI) via hydroxyl (water molecules) and silicate groups.