Growth Inhibitors and their Antagonists as Mutagens and Antimutagens in Escherichia coli

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Abstract
Thirty-five substituted benzimidazoles, benzotriazoles and quinoxalines were tested as growth inhibitors on three mutants of Escherichia coli, strain W, having different purine requirements, and on the ciliate Tetrahymena geleii. Both organisms were affected in a similar way by the compounds. A number of the compounds, especially those with a nitro group on the benzene ring, were inhibitory. Several analogues were tested for mutagenic activity at the purine and streptomycin loci in a purine-requiring mutant of E. coli. Only inhibitory compounds were found to be mutagenic; non-inhibitory concentrations of one inhibitory analogue, 4-nitro,6-hydroxy-benzimidazole (NHB), were, however, also mutagenic. No specific mutagenesis was demonstrated. NHB increased the rate of mutation as determined by the papilla method. The hypothesis was eliminated that selection rather than mutagenesis was involved. NHB did not increase the frequency of mutants in non-dividing cells and was not incorporated into bacterial DNA. DNA and RNA and their constituents, purine and pyrimidine precursors and analogues, vitamin B12 and other vitamins, have no effect on the inhibition or mutagenesis by NHB. Several amino acid combinations and one non-mutagenic analogue (4-hydroxy, 6-nitro-benzotriazole) were found to interfere with mutagenesis by NHB. These compounds did not affect the frequency of spontaneous mutants. Mutagenesis by 5-nitroquinoxaline, a pterln analogue, was depressed by amino acids in the same purine-requiring mutant. The reversal of mutagenic activity by amino acids is strain and mutagen specific. Twenty-five known inhibitors of nucleic acid synthesis and antagonists to inhibition were tested for mutagenic activity in five strains of Escherichia coll. Several, including 6-mercaptopurine, were mutagenic; NHB, 5-nitroquinoxaline and 5-aminouracil were mutagenic in most of the strains tested. The mutagenic activity of 5-aminouracil was not reversed by thy mine, thymidine or other nucleic acid components, but the mutagenesis of 6-mercaptopurine was annulled by purine bases and by ribosides.