Conversion of selenite to elemental selenium by indigenous bacteria isolated from polluted areas

The present research work is on the biotic transformation of highly soluble and toxic selenite to less toxic elemental selenium using bacterial strains Bacillus subtilis, Exiguobacterium sp., Bacillus licheniformis, and Pseudomonas pseudoalcaligenes. The conditions were optimized by changing different physical parameters such as pH, temperature, different Selenium (Se) concentration levels (200, 400, and 600 μg ml−1), aeration, and incubation time for increased selenite reduction. The Se reduction rate increased with increase in pH. On average, 28–90% selenite reduction was observed at pH 9, while 15–33% at pH 3. To check the optimum temperature, all strains were cultured at three temperatures 32, 37, and 42 °C. Selenite reduction was observed at various temperatures and the results show that each strain has different preferences for optimum Se reduction. Selenite reduction was also monitored using different initial selenite concentrations and the results showed that at lower initial concentration (200 μg ml−1) maximum Se was reduced. This study showed that selenite-reducing bacteria can remediate Se in both aerobic and anaerobic environments, as well as their reduction ability decreases with increase in incubation time.