Action of X-Irradiation on E. coli

Escherichia coli used in the present experiment were obtained from a 4-hour culture at 37?C in peptone-water medium (peptone 1 %, NaCI 0.5 %, in distilled water). Cells from this mother culture were freed from the culture medium by repeated centrifugation and washing with phosphate buffer at pH 7.0. The purified cells, suspended in a few milliliters of the same buffer, were used in the different experiments. The source of radiation was 70-kv. X-rays filtered by 4-mm aluminum. The specimens were irradiated in a Plexiglas chamber which fitted in the X-ray tube window just behind the filter. The specimen chamber had slots cut in it so that the samples were always placed in the same position with respect to the source of radiation. The dose of radiation with the Plexiglas chamber in the path was measured carefully with the help of a Victoreen dosimeter placed at the specimen position with an accuracy of ?2 %. The dosage rate was 690 r/min. For irradiation in both the dry and the wet condition, glass slides coated with thin films of gelatin were used (7). For irradiation in the wet condition, small drops