Background and Objectives: Heavy metals pollution is one of the most important concerns in the world. Selenium is one of the most important elements for the life, but if the absorption of this element in cells increases, it acts as a toxic element. Materials and Methods: In this study, bacterial isolates were screened and isolated from selenium-contaminated soil and water. Twenty -five out of 42 isolates were able to reduce Selenite. Also, the response surface method (RSM) was used to evaluate and optimize the biological reduction of selenite by Selena 3. Factors of bacterial inoculation percentage, time, and amount of selenium oxyanion salt concentration were studied at five levels of -α, -1, 0, +1, and +α. Results: Bacillus sp. Selena 3 was able to reduce 80 mM sodium selenite in less than 4 hours compared to other bacterial isolates. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of sodium selenite Bacillus sp. Selena 3 was reported as 160 and 320 mM, respectively. The results showed that with increasing duration, the percentage of selenite reduction by bacteria increases and the percentage of bacterial inoculation does not have much effect on its reduction. Conclusion: Due to the ability of Bacillus sp. Selena 3 for rapid reduction in significant concentration of selenium oxyanion (SeO32-), this bacterium can be used as an efficient candidate in removing selenite in the environment.
