Bioremediation Performance of Recombinant Shewanella azerbaijanica; Considering Uranium Removal in the Presence of Nitrate.

Genetic engineering in microorganisms has emerged as a promising approach for pollutant removal from industrial wastewater. Shewanella azerbaijanica has the ability to reduce uranium. This study examined the impact of high-nitrate concentrations on uranium bioreduction in both native and recombinant bacterial strains. Bacterial performance was evaluated in terms of uranium bioreduction (measured via ICP-AES method), and survival in anaerobic conditions (measured via Neubauer chamber counting) in the presence of uranium and nitrate over various time intervals (24 h, 1 week, 4 weeks, 4 months, and 9 months). Although the recombinant strain showed a lower cell population than the wild-type strain, it achieved 20% higher uranium reduction after 24 h of incubation in uranium and nitrate-containing conditions. This suggests that the genetic modifications enhanced extracellular electron transfer (EET). The improved bioremediation efficiency may be attributed to the cloned mtrC gene, which promotes more effective electron transfer in Shewanella bacteria. Additionally, uranium removal may have been further enhancedby the inactivation of the napB gene using the SDM method. This high-performance trends was consistent across all time intervals. In wild-type S. azerbaijanica uranium removal rates were74%, 54%, 96 and 99% after 1 week, 4 weeks, 4 months, and 9 months, respectively. Inrecombinant bacteria, these rates increased to 91%, 78%, 96%, and 100% at the same time points. The bioreduction mechanism was further confirmed by X-ray diffraction (XRD) analysis, which verified the ability of S. azerbaijanica to reduce uranium in the presence of nitrate. Overall, this study identifies the recombinant bacterium as promising candidate for future metal bioreduction research.