The immobilization and reduction of uranyl (UO22+) by Sulfobacillus thermosulfidooxidans under aerobic conditions.

Uranium (U) released from mining activities poses a threat to human and environmental health. Bioleaching bacteria are common in mining environments and play a significant role in uranium mobility. However, the relationship between the Fe/S-oxidizing bacterium Sulfobacillus thermosulfidooxidans and uranium remains poorly understood. In this study, we investigated the interaction between U(VI) and S. thermosulfidooxidans under sulfate-rich and aerobic conditions. The strain demonstrated the capacity to immobilize uranium under acidic conditions. S. thermosulfidooxidans grown on S0 exhibited a higher uranium immobilization capacity than on FeS2 (34.8 mg g-1 at pH 4.2), with a uranium loading of 70.1 mg g-1 under pH 3.9 and initial uranium of 20 ppm. Spectroscopic analyses confirmed that U(VI) was reduced to U(IV) during the aerobic immobilization process, and intracellular uranium accumulation occurred in association with phosphorus. The uranium reduction process and sulfur oxidation occurred concurrently, as indicated by a decrease in reduced sulfur species when uranium was present. The dynamic analysis of uranium reduction revealed competition between the bioadsorption and U(VI) reduction processes. These findings provide evidence that S. thermosulfidooxidans can immobilize uranium through biosorption, bioaccumulation, and partial U(VI) reduction under acidic and aerobic conditions. The results provide new insights into uranium biotransformation in mining environments and have important implications for land management and environmental remediation.