Isolation and identification of a novel As-reducing bacterium for the reductive dissolution of scorodite

Abstract:

[Objective] This study aimed to investigate the reductive dissolution of scorodite by an indigenous As-resistant bacterium isolated from the Jianghan plain and the influences of nitrate and sulfate on the mobilization in this microbiological process.[Methods] We used the microbial enrichment technique to isolate a facultative anaerobic arsenate-reducing strain (A11), amplified the 16S rRNA and functional genes (arsenate-reductase gene, thiosulfate reductase gene and nitrate reductase genes) from the bacterial cells, and analyzed arsenate-, ferric iron-, thiosulfate-, and nitrate-reducing activities of this strain. We also examined the abilities of A11 cells to catalyze the mobilization and release of As and Fe from scorodite under anaerobic conditions, and further explored how sulfate and nitrate affected this microbial process. The microbial reduction and dissolution of the scorodite mineral were verified by XRD and SEM-EDS analysis. [Results] Citrobacter sp. A11 completely reduced 0.45 mmol/L As(V), 2 mmol/L S₂O₃^2-, 1 mmol/L Fe(III) and 140 mg/L NO₃^- in 4 days, 6 days, 3 days, 28 hours, respectively. In the presence of A11 cells, approximately 33.68 μmol/L As(III) and 51.93 μmol/L Fe(II) were released from the scorodite slurries after 28 days of anaerobic incubations. The presence of sulfate caused 41.04% and 34.30% increases of the A11-catalyzed release of As(III) and Fe(II) over the course of 28 days. However, the addition of nitrate caused 35.07%, 53.46% decreases of the A11-catalyzed release of As(III) and Fe(II), respectively. XRD and SEM-EDS observations for the reduced scorodite revealed that the mineral particles were altered dramatically. The particles size of the treated scorodite was much smaller than the control one. [Conclusion] Citrobacter sp. A11 strain has been identified with the ability of arsenate, thiosulfate, ferric iron and nitrate reduction, also can efficiently catalyze the mobilization and release of As and Fe from scorodite under anaerobic conditions, and this process enhanced when sulfate was added to the reactions. However, this process was inhibited when nitrate was added.