The immobilization mechanism of U(VI) induced by Bacillus thuringiensis 016 and the effects of coexisting ions

Abstract

Nonreductive biomineralization is a cost-effective method to remediate uranium (U) contaminated wastes. In this work, we explored the immobilization mechanism of U(VI) induced by Bacillus thuringiensis 016. Enzymes denaturation and functional groups shielding experiments revealed that the biosorption of uranium by B. thuringiensis 016 was a nonenzymatic process in which phosphate, amino, and carboxyl groups played a major role. Fe3+ and CO32− had a strong ability to inhibit uranium biosorption. The biomineralization of uranium by B. thuringiensis 016 was a synergistic effect of enzymes and cell metabolism. In addition, K+, Na+, and Mg2+ slightly promoted the ability of bacteria to mineralize U(VI). Besides, when the initial uranium concentration was 100 mg/L, the reaction of B. thuringiensis 016 with uranium was a rapid process consisting of extracellular biosorption and intracellular biomineralization. When the initial uranium concentration exceeded 200 mg/L, B. thuringiensis 016 can only adsorb uranium. Furthermore, by tracking the concentration of soluble U(VI) in the cells, it was confirmed that the amorphous compounds, formed on the cell surface, were an insoluble form when entering the cells. Our findings provide a further understanding of the mechanisms of uranium immobilization, which would be useful for the application of B. thuringiensis 016 in uranium pollution treatment.