Selenium uptake and immobilization using indigenous Bacillus strain isolated from seleniferous soils of Punjab

Selenium is an essential trace element inevitably present in almost all the soils. It exists in the various chemical forms at a particular site due to the various features such as pH, organic matter, concentration of cations and anions of the site. An excessive concentration of selenium has been reported in various regions of Punjab. The present research has explicated the mobility of selenium by indigenous bacterial strains isolated from seleniferous soil of Punjab, India. Physiochemical characterization of the soil sample indicated alkaline nature which in turns favors the existence and mobility of selenium oxyanions in the soil. A significant concentration of selenium (2.652 mu g/g) has been reported in the soil sample. Total four bacterial strains were isolated from the soil based on their growth in selenium oxyanions supplemented medium. Bacterial isolate SGB-5 was explored for selenium sequestration and transformation studies on the basis of tolerance to selenium oxyanions especially selenate. ICP-MS analysis of biomass indicated significant sequestration of selenium (upto 70%) by the isolate SGB-5. X-ray diffraction spectrum of biomass associated selenium revealed the reduced and crystalline nature of selenium in the biomass. SEM-EDX analysis further confirmed the accumulation of nano-sized elemental selenium around the bacterial cells. Further SGB-5 strain was characterized and identified as Bacillus sp. using 16S rRNA gene sequencing.