Complexation of Uranium by Cells and S-layer Sheets of Bacillus sphaericus JG-A12

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) with an ability to bind uranium and other heavy metals. By using a phosphoprotein specific staining, Inductive Coupled Plasma- Mass Spectrometry (ICP-MS) analysis and a colorimetric method, purified and recrystallized S-layer proteins were shown to be phosphorylated. We used Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, the complexation of uranium by the vegetative bacterial cells was studied. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å, and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission Electron Microscope (TEM) analysis showed that the uranium accumulated by the cells of this strain is located at the cell surface as dense deposits.