Mohaddeseh Khalilian - MSc of Microbiology, Department of Microbiology, Faculty of Basic Sciences, Islamic Azad University, Qom Branch, Qom, Iran
Mohammad Reza Zolfaghari - Assistant Professor, Department of Microbiology, Faculty of Basic Sciences, Islamic Azad University, Qom Branch, Qom, Iran
Mohammad Soleimani - Assistant Professor, Department of Microbiology, Faculty of Basic Sciences, Islamic Azad University, Qom Branch, Qom, Iran
Mohammad Reza Zand Monfared - MSc of chemistry, Department of Chemistry, Faculty of Basic Sciences, Islamic Azad University, Qom Branch, Qom, Iran

Introduction: Selenium oxyanions are toxic to living organisms at excessive levels. Selenite can interfere with cellular respiration, damage cellular antioxidant defenses, inactivate proteins by replacing sulfur, and block DNA repair. Microorganisms that are exposed to pollutants in the environment have a remarkable ability to fight the metal stress by various mechanisms. These metal-microbe interactions have already found an important role in bioremediation. The objective of this study was to isolate and characterize a bacterial strain with a high potential in selenite bioremediation.Methods: In this study, ۲۶۳ strains were isolated from wastewater samples collected from selenium-contaminated sites in Qom, Iran using the enrichment culture technique and direct plating on agar. One bacterial strain designated QW۹۰, identified as Bacillus sp. by morphological, biochemical and ۱۶S rRNA gene sequencing, was studied for its ability to tolerate high levels of toxic selenite ions by challenging the microbe with different concentrations of sodium selenite (۱۰۰-۶۰۰ mM).Results: Strain QW۹۰ showed maximum Minimum Inhibitory Concentration (MIC) to selenite (۵۵۰ mM) and the maximum selenite removal was exhibited at ۳۰ degrees C, while the activity was reduced by ۲۰% and ۳۳.۸% at ۲۵ and ۴۰ degrees C, respectively. The optimum pH and shaking incubator for the removal activity were shown to be ۷.۰ and ۱۵۰ rpm at ۵۰.۷% and ۵۰.۸%, respectively. Also, the concentration of toxic sodium selenite (۸۰۰ μg/ml) in the supernatant of the bacterial culture medium decreased by ۱۰۰% after ۲ days, and the color of the medium changed to red due to the formation of less toxic elemental selenium.Conclusion: This study showed that the utilization of enrichment culture technique in comparison to the direct plating on agar leads to better isolation of selenite resistant bacteria. Bacterial strain was resistant to high concentrations of selenite and also it reduced selenite to red elemental selenium. Therefore, this microorganism could be further used for bioremediation of contaminated sites.

Bioremediation, Bacterial strain, MIC, Selenite