RESUMO
Gamma-ray-irradiated medium is found to produce an immediate slowing of respiration in cells of Escherichia coli 15 T-L-. It also introduces a lag in cell division that can be shortened by the presence of methylene blue and potassium cyanide. The lag is absent if the cells are grown anaerobically. These results suggest that the peroxides produced by irradiating medium block the electron transport system. Since cells concentrate peroxides, the loss of this function induced by bombardment was used to deduce the target molecular weight of the enzyme responsible. It is 73,000.
Assuntos
Escherichia coli/fisiologia , Escherichia coli/efeitos da radiação , Consumo de Oxigênio/fisiologia , Oxigênio/metabolismo , Peróxidos/metabolismo , Aerobiose/fisiologia , Aerobiose/efeitos da radiação , Anaerobiose/fisiologia , Anaerobiose/efeitos da radiação , Proliferação de Células/efeitos da radiação , Sobrevivência Celular/efeitos da radiação , Relação Dose-Resposta à Radiação , Transporte de Elétrons/fisiologia , Transporte de Elétrons/efeitos da radiação , Escherichia coli/citologia , Raios gama , Consumo de Oxigênio/efeitos da radiação , Doses de RadiaçãoRESUMO
The present report summarizes data from experiments investigating a correlation between cellular capacity to synthesize macromolecules and the extent of deoxyribonucleic acid (DNA) degradation in bacteria exposed to ionizing radiation. It is shown that a relationship exists between conditions leading to an increase in degradation and those that would be expected to inhibit the induction of a prophage. Since the organisms used were known to harbor a defective prophage, additional experiments were carried out comparing under various conditions the response to ionizing radiation of Escherichia coli 15 T- and a cured derivative. In addition, an effort was made to relate the presence of the defective prophage to colony-forming ability after irradiation. The results led to the hypothesis that the presence of the prophage results in less degradation than would otherwise be observed and may also be responsible for increased survival under certain conditions.
Assuntos
Técnicas de Cultura de Células/métodos , Dano ao DNA/fisiologia , DNA Bacteriano/efeitos da radiação , Escherichia coli/fisiologia , Escherichia coli/efeitos da radiação , Glucose/metabolismo , Prófagos/fisiologia , Proliferação de Células/efeitos da radiação , Sobrevivência Celular/efeitos da radiação , Relação Dose-Resposta à Radiação , Escherichia coli/citologia , Escherichia coli/virologia , Doses de Radiação , Radiação IonizanteRESUMO
In the experimentally observed relationship between survival of colony-forming ability and the amount of exposure to ultraviolet light, two characteristics are generally found. First, sensitive and resistant components often show. Second, there is often a shouldered character to the survival. We present evidence that the first is largely due to the presence of active replication forks in the genome, and that the second is related to the operation of the recombinational repair system. We are able to describe our data in terms of a superposition of single and multiple-hit fractions and to show that the latter are greatly increased, in excision-repair-competent strains, by prevention of protein synthesis for 1 h prior to irradiation. Applying this analysis and treatment to a number of mutant strains enables us to make suggestions as to the interaction between recombinational and excision repair.