Effects of thermoradiation treatments on the DNA of bacillus subtilis endospores

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. 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. Bacillus subtilis spores were treated at combinations of 33 kr/hr, 15 kr/hr, 105°C, 85°C, 63°C, and 50°C. 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. In cases displaying synergism of spore killing, single strand breakage while the DNA was in a denatured state is suspected as a likely mechanism.