Immobilization of Bacterial Cells in Hydrogels Prepared by Gamma Irradiation for Bioremoval of Strontium Ions

Cross-linking of polymer hydrogels can be achieved by exposing the polymer to gamma radiation that induces production of polymer chain radicals resulting in cross-linking of chains. The present study was focused on fabrication of hydrogel by gamma irradiation for immobilization of bacterial cells. Hydrogels were prepared using 30 and 40% acrylamide at gamma irradiation dose of 5 kGy. Five bacterial strains BR-6, BR-14, BR-18, BR-21, and BR-26 screened for resistance to strontium were immobilized in hydrogels and evaluated for the bioremoval of strontium. Strontium content for different strains was 4.21-4.68 mu g/ml after 3 days in the presence of free cells grown in 5 mu g/ml strontium, while for immobilized cells, the strontium content was 3.35-3.81 mu g/ml (30% acrylamide gel) and 3.46-3.99 mu g/ml (40% acrylamide gel). After 10 days of incubation, the strontium content was reduced to 0.94-1.26 mu g/ml (30% acrylamide gel) and 0.82-1.07 mu g/ml (40% acrylamide gel), and for free cells, strontium content was 1.34-1.41 mu g/ml. 72-75% bioremoval of strontium by free cells of different strains BR-6, BR-14, BR-18, BR-21, and BR-26 was observed after 10 days of incubation. 77-83% reduction in strontium content was observed in the presence of cells immobilized in 30% acrylamide, whereas higher reduction of 80-85% was observed for cells immobilized in 40% acrylamide after 10 days. At higher concentration of 10-mu g/ml strontium, 62 to 71% reduction was observed with immobilized bacterial cells. Obtained results indicated that immobilized bacterial cells in hydrogels prepared by gamma irradiation were found to have significantly higher efficiency as compared to free cells for bioremoval of strontium ions.