Complex formation of U(VI) with Bacillus-isolates from a uranium mining waste pile

Abstract

Accumulation studies with vegetative cells and spores of three Bacillus isolates (JG-A 30, JG-A 12, JG-A 22, classified as Bacillus cereus, Bacillus sphaericus, Bacillus megaterium) from a uranium mining waste pile (Johanngeorgenstadt, Saxony) and their corresponding reference strains have shown that Bacilli accumulate high amounts of U(VI) in the concentration range examined (11-214 mg/L). Information on the binding strength and the reversibility were obtained from extraction studies with different extractants. With 0.01 M EDTA solution the uranium bound to the biomass was released almost quantitatively. The characterization of the bacterial-UO22+-complexes by time-resolved laser fluorescence spectroscopy (TRLFS) showed the formation of inner-sphere complexes with phosphate groups of the biomass. The results lead to the conclusion that the cell wall components with phosphate residues e.g., polysaccharides, teichoic and teichuroic acids or phospholipide layers of the membranes are responsible for the uranium binding. The spectroscopic studies of the U(VI)-complexes with isolated bacterial cell walls and isolated surface-layer proteins of the strain Bacillus sphaericus NCTC 9602 after cell fractionation have shown that the complexation of U(VI) with intact cells (vegetative cells or spores) is different from the coordination with isolated cell wall components, especially with the S-layer proteins. For all Bacillus strains studied in this work, a significant contribution of the S-layer proteins to the binding of uranyl to living cells can be excluded.