| Endospores of the bacterium, Bacillus subtilis, have been shown to exhibit a synergistic rate of cell death when treated with particular levels of heat and ionizing radiation in combination. This synergism has been documented for a number of different organisms at various temperatures and radiation doses (Sivinski, H. D., D. M. Garst, M. C. Reynolds, C. A. Trauth, Jr., R. E. Trujillo, and W. J. Whitfield, “The Synergistic Inactivation of Biological Systems by Thermoradiation,” Industrial Sterilization, International Symposium, Amsterdam, 1972, Duke University Press, Durham, NC, pp. 305–335). However, the mechanism of the synergistic action is unknown. This study attempted to determine whether the mechanism of synergism was specifically connected to the DNA strand breakage—either single strand breakage or double strand breakage. Some work was also done to examine the effect of free radicals and ions created in the spore body by the radiation treatments, as well as to determine the functionality of repair enzymes following heat, radiation, and thermoradiation treatments. Bacillus subtilis spores were treated at combinations of 33 kr/hr, 15 kr/hr, 105°C, 85°C, 63°C, and room temperature. Some synergistic correlation was found with the number of double strand breaks, and a strong correlation was found with the number of single strand breaks. DNA was damaged more by irradiation in the naked state than when encased within the spore, indicating that the spore encasement provides an overall protective effect from radiation damage in spite of free radicals and ions which may be created from molecules other than the DNA molecule within the spore body. Repair enzymes appeared to be functional in their ability to repair single and double strand breaks following treatments by radiation only, heat only, and thermoradiation. |
