Selenium Metabolizing Capabilities of 12 Bacterial Strains Isolated from Urban Environmental Samples

The role of bacterial selenium metabolism in non-polluted environments remains underexplored within the selenium biogeochemical cycle. In this study, selenium-metabolizing bacteria were isolated from urban environmental samples. Among 12 isolates, 10 were identified as <i>Citrobacter</i> spp., while the remaining 2 were <i>Scandinavium hiltneri</i> and <i>Klebsiella aerogenes</i>. The <i>Citrobacter</i> isolates demonstrated high selenium-removal efficiency, removing over 95% of 5 mM selenium from the aqueous phase within one week. In contrast, <i>S. hiltneri</i> K24-1 and <i>K. aerogenes</i> K24-4 removed only 19% and 69%, respectively. A detailed investigation of five representative isolates, <i>C. freundii</i> K21-1, <i>S. hiltneri</i> K24-1, <i>C. braakii</i> K24-2, <i>K. aerogenes</i> K24-4, and <i>C. freundii</i> K24-5, revealed that <i>Citrobacter</i> spp. efficiently reduced selenate directly to elemental selenium, with minimal accumulation of selenite intermediates. These results highlight <i>Citrobacter</i> spp. as key selenium reducers and suggest their potential as bioindicators of selenium metabolic capacity in the environment.