W-reactivation of phage lambda in X-irradiated mutants of Escherichia coli K-12.

The survival of UV irradiated phage lambda was increased on X-irradiated E. coli K-12 host cells over that on unirradiated cells. The frequency of c mutants among the surviving phages was to a similar extent increased by the X-ray exposure of the host cells as by UV light. This W-reactivation of phage lambda occurred in uvrA, polA, and recB mutants besides the wild type at about equal X-ray doses, however, at a reduced reactivation efficiency compared with the wild type. W-reactivation was undetectable in recA mutants. While maximal UV induced W-reactivation occurred 30 min after irradiation, the maximal X-ray induced reactivation was found immediately after irradiation. Chloramphenicol (100 micrograms/ml) and nitrofurantoin (50 micrograms/ml) inhibited W-reactivation of phage lambda if added before irradiation of the host cells, indicating the necessity of protein synthesis for W-reactivation.