Repair effects of exogenous SOD on Bacillus subtilis against gamma radiation exposure

Superoxide dismutase (SOD) is an enzyme that removes free radicals from cells in many organisms. In order to further characterize these repair effects and their mechanism when subjected to radiation, Bacillus subtilis cells were exposed to gamma radiation and the cell survival rate, intracellular SOD activity, and DNA double-strand breakage were investigated. Vegetative cells of B. subtilis were irradiated by 60Co gamma radiation at varying doses and subsequently exposed to varying levels of exogenous SOD. Standard plate-count, xanthine oxidase, and pulsed-field gel electrophoresis (PFGE) methods were employed to investigate the repair effects. The results showed that the exogenous SOD could significantly improve cell survival rate and intracellular SOD activity after gamma radiation. The cell survival rate was elevated 30-87 times above levels observed in control samples. Adding exogenous SOD into gamma irradiated cells may dramatically increase intracellular SOD activity (p < 0.01), while percentage of DNA release (PR) values may decrease significantly when cells are treated with SOD. The repair effects were observed to vary with the gamma radiation dose and SOD concentration. These findings suggest that exogenous SOD may have the ability to repair vegetative B. subtilis cell damage after irradiated by gamma radiation. DNA strand scission may also be prevented by addition of SOD. This research contributes to better understanding of protection from the effects of free radicals and their mechanisms, an ongoing process in many organisms that involves the cellular response to gamma radiation, which occurs naturally in soil and water, as well as in unusual cases of high-dosage exposure.