Inaktivierende und mutagene Wirkung salpetriger Säure auf Zellen von Escherichia coli

Abstract

Cells of E. coli B incubated with NaNO₂ undergo inactivation. In non-metabolizing cells the inactivation follows a two hit curve. In metabolizing cells the rate of inactivation is increased and the inactivation curve does not show two-hit kinetics. The rate of inactivation decreases with rising pH and decreasing NaNO₂-concentration. Therefore nitrous acid appears to be the active substance. Nitrous acid proved to be a potent mutagen as shown by isolation of auxotrophic mutants. With an inactivation rate of 10^-4 about 1.4 per cent of the surviving cells were auxotrophs. The probability that this increase in mutants may be due to selection during inactivation of auxotrophs present before exposure was excluded experimentally. In none of 559 auxotrophic colonies grown from single cells which had survived contact with nitrous acid wild-type sectors were found. For metabolizing and nonmetabolizing cells the increase of the percentage of auxotrophic mutants with increasing time of exposure to HNO₂ followed a two-hit curve. In these experiments the percentage of induced mutants was independent of the different rate of inactivation caused by different states of metabolism and dependent only on the time of incubation with nitrous acid. The results are discussed as being in agreement with the assumption that in non-metabolizing cells nitrous acid acts directly on the cellular DNA leading to inactivation and mutation.