Heavy ion induced DNA double strand breaks in cells of E. coli.

Vegetative cells of E. coli differing in their radiosensitivity have been used in heavy ion irradiation experiment. Besides inactivation measurements also the induction of DNA double strand breaks (DSB) have been measured using the method of pulse-field gel electrophoresis. This method allows to separate linear DNA with length up to 8 Mio base pairs. After irradiation with heavy ions we find a higher amount of low molecular weight fragments when compared to sparsely ionizing radiation. This agrees with the idea that heavy ions as a structured radiation have a high probability to induce more than one strand break in a DNA molecule if the particle hits the DNA. The amount of intact DNA remaining in the agarose plugs decreases exponentially for increasing radiation doses or particle fluences. From these curves cross sections for the induction of DSB after heavy ion irradiation have been determined. These results will be discussed in comparison to the results for cell survival.