Induction of the SOS response and mutations by reactive oxygen-generating compounds in various Escherichia coli mutants defective in the mutM, mutY or soxRS loci.

Abstract

Derivatives of E. coli WP2s (uvrA trpE) defective in 7,8-dihydro-8-oxoguanine (8-OG) DNA glycosylase activity (mutM), MutY glycosylase activity on an A:8-OG mispair (mutY), and/or an adaptive response to oxidative stress by superoxide (soxRS) were constructed to compare the mutability to various reactive oxygen-generating compounds. Induction of Trp+ reversion was assayed both in the presence and absence of plasmid pKM101. Phenazine methosulfate and phenazine ethosulfate showed mutagenic activity at a relatively low dose in soxRS mutants. In comparison to the parent strain WP2s, however, the introduction of mutM, mutY, or soxRS mutations, in any combination, did not make the strain hypersensitive in terms of mutability (i.e. mutation induction at relatively low doses) to hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, or phenylhydrazine. Mutagenicity of formaldehyde was detected only in the pKM101-carrying strains. On the other hand, bleomycin, menadione, plumbagin, paraquat, and diquat were not mutagenic to any strain, with or without pKM101. The SOS-response inducing activity was measured by monitoring the expression of a umu'-'lacZ fusion gene, carried on the plasmid pSK1002. The induction of the SOS response by hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, formaldehyde, phenylhydrazine, and bleomycin was of almost the same magnitude between the parent strain and a mutM or soxRS mutant. Phenazine methosulfate and phenazine ethosulfate induced the SOS response only in the soxRS derivatives. No induction was detected by treatment with redox-cycling compounds, such as menadione, plumbagin, paraquat, or diquat.