Insight into the complexation of uranium with Bacillus sp. dwc-2 by multi-spectroscopic approaches: FT-IR, TRLF and XAFS spectroscopies

Abstract

The micromechanisms of the interactions between uranium and microorganisms, especially chemical bonds and bonding numbers between uranium and microbe are not yet clear. In this work, uranium coordination with functional groups in/on Bacillus sp. dwc-2 has been rationally explored by X-ray absorption fine structure (XAFS), Fourier transform infrared (FT-IR), time-resolved laser-induced fluorescence (TRLF) spectroscopies. The results indicate that under acidic condition, 66.8 % of O atoms in coordination shell of U(VI) equatorial plane are provided by organic phosphoryl groups via monodentate coordination, 18.8 % and 15.5 % are provided by water molecules and carboxyl groups via monodentate and bidentate coordination, respectively. While under alkaline condition, these proportions change to 53.1 %, 34.4 % and 22.0 %, respectively. Under neutral condition, U(VI) is mainly deposited by complexing with inorganic phosphates released by microbial cells. Under anaerobic condition, partial U(VI) can be reduced to U(IV) which primarily complex with phosphorus containing groups via monodentate and bidentate coordination, existing as amorphous solids or coordination polymers. This is the first exploration of the binding mechanism between uranium and microorganisms at a semi-quantitative level under different conditions. Our studies will further enhance the contribute to the understanding of coordination mechanism of uranium with microorganism, and demonstrate the potential bioremediation value of this bacterium.