title: Effects of ionizing radiation on synchronous cultures of Escherichia coli B-r.
abstract: The sensitivity of Escherichia coli B/r to X-irradiation is correlated with the replication cycle of deoxyribonucleic acid (DNA). The sensitivity to X-irradiation in the wild type can be attributed to the presence of nuclear targets plus DNA repair mechanisms. The effects of nuclear targets are observed in the recombination-deficient (rec-) mutant B/r, but the sensitivity reflected by changes in the slope of killing curves is absent. A study of different growth conditions indicates that maximal resistance to X rays occurs toward the middle of the division cycle. Evidence is offered that branched chromosomes respond as one-hit targets to X-irradiation. The killing effects of heavy-ion bombardment on E. coli are due primarily to ionizing radiation.
mesh_terms: D002455:Cell Division; D003470:Culture Media / Q000494:pharmacology; D004261:DNA Replication / Q000528:radiation effects*; D004269:DNA, Bacterial / Q000528:radiation effects; D004926:Escherichia coli / Q000254:growth & development / Q000528:radiation effects*; D011830:Radiation Effects; D011831:Radiation Genetics
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial