Stimulation of mutations suppressing the loss of replication control by small alcohols

Abstract

Transient exposure of lysogenic Escherichia coli cells to small alcohols stimulated the frequency of mutations suppressing the lethal loss of replication control from a prophage fragment of bacteriophage λ. The stimulation in mutation frequency paralleled the effect of mutagenic agents, and in this sense the alcohols behaved as mutagens. 10-min treatments above distinct threshold concentrations at 23%, 18%, 10% and 4% (v/v) were required in order for methanol, ethanol, isopropanol and propanol to evoke mutagenic effects. The selected mutant cells were, in general, equally or more sensitive to ethanol than the starting cells. The mutagenicity of methanol and ethanol was detected only with E. coli strains with λ fragments that included the site-specific and general recombination genes found within the phage int-kil gene interval; whereas, stimulation of the frequency of phenotypically identical mutations by nitrosoguanidine or ionizing radiation did not require that the λ fragment encode these genes. Treatments of lysogenic cells with mutagenic concentrations of ethanol did not trigger prophage induction and were concluded no to induce a cellular SOS response nor to denature the prophage repressor, or to disrupt repressor-operator binding. The toxicity of ethanol was pH-dependent. Cellular sensitivity to ethanol toxicity was unaffected by the integrated λ fragment(s) or by an intact λ prophage; but, it was increased by deletions of the E. coli chromosome extending rightward from bio into uvrB, and rightward from chlA.