Interference with Respiratory Control by Ionizing Radiations in Escherichia Coli B/r

Summary

Irradiation of log-phase Escherichia coli B/r cells with ⁶⁰Co γ-rays (30 krads) causes respiration to cease about 40 min after irradiation. When glycerol is the carbon source, cessation is complete for several hours. Addition of casamino acids or substitution of glucose for glycerol favours early recovery. Respiration does not turn off when 5-fluorouracil (FU), rifampin, or chloramphenicol is added immediately after irradiation. In all these situations, the behaviour of γ-irradiated cells resembles that of cells irradiated with ultraviolet (u.v.) light, and we conclude that in both cases RNA synthesis and protein synthesis are necessary for respiration to be turn off. Unlike u.v.-irradiated cells, in which an early increase in viability is favoured by maintenance of respiration with FU treatment, addition of this analogue to γ-irradiated cells completely prevents even the normal exponential increase in viability, which begins about 60 min after irradiation. We conclude that RNA synthesis is necessary for a step in the repair of DNA or in the subsequent recovery process.