Independent and synergistic bio-reductions of uranium (VI) driven by zerovalent iron in aquifer

Zerovalent iron [Fe(0)] can donate electron for bioprocess, but microbial uranium (VI) [U(VI)] reduction driven by Fe(0) is still poorly understood. In this study, Fe(0) supported U(VI) bio-reduction was steadily achieved in the 160-d continuous-flow biological column. The maximum removal efficiency and capacity of U(VI) were 100% and 46.4 +/- 0.52 g/(m(3).d) respectively, and the longevity of Fe(0) increased by 3.09 times. U(VI) was reduced to solid UO2, while Fe(0) was finally oxidized to Fe(III). Autotrophic Thiobacillus achieved U(VI) reduction coupled to Fe(0) oxidation, verified by pure culture. H2 produced from Fe(0) corrosion was consumed by autotrophic Clostridium for U(VI) reduction. The detected residual organic intermediates were biosynthesized with energy released from Fe(0) oxidation and utilized by heterotrophic Desulfomicrobium, Bacillus and Pseudomonas to reduce U(VI). Metagenomic analysis found the upregulated genes for U(VI) reduction (e.g., dsrA and dsrB) and Fe(II) oxidation (e.g., CYC1 and mtrA). These functional genes were also transcriptionally expressed. Cytochrome c and glutathione responsible for electron transfer also contributed to U(VI) reduction. This study reveals the independent and synergistic pathways for Fe(0)-dependent U(VI) bio-reduction, providing promising remediation strategy for U(VI)-polluted aquifers.

Automated summary

This study demonstrates the successful application of zerovalent iron (Fe(0)) for the biological reduction of uranium (VI) [U(VI)]. The experiments conducted in a continuous-flow biological column showed that Fe(0) supported U(VI) reduction achieved a maximum removal efficiency of 100% and a capacity of 46.4 +/- 0.52 g/(m(3).d). The longevity of Fe(0) was also significantly increased. Metagenomic analysis revealed the upregulation of genes involved in U(VI) reduction and Fe(II) oxidation. This research provides a promising remediation strategy for U(VI)-polluted aquifers.