Inhibition and induction of SOS responses in Escherichia coli by cobaltous chloride.

Mutagenesis induced by several genotoxic agents has been reported to be inhibited by cobaltous chloride. In order to study the effects of this metal in some SOS functions we evaluated mutagenesis, lysogenic induction and phage reactivation in Escherichia coli cells treated with CoCl2. We detected that cobaltous chloride, when present in the plating medium, was able to block mutagenesis and lysogenic induction promoted by UV irradiation. We also found that CoCl2 blocked protein synthesis, so we propose that this effect can be responsible for the antimutagenic and antilysogenic effects of this metal. On the other hand, if the cells were treated for a short period of time with CoCl2, in the absence of Mg, we observed that cobaltous chloride per se was able to promote lysogenic induction as well as to enhance the phage reactivation induced by UV irradiation. We conclude that depending on experimental conditions, cobaltous chloride may act either as an inhibitor or as an inducer of the SOS functions.