Sodium arsenite inhibits spontaneous and induced mutations in Escherichia coli

Sodium arsenite at a non-toxic concentration was found to inhibit strongly mutagenesis induced by ultraviolet light (UV), 4-nitroquinoline-1-oxide (4NQO), furylfuramide (AF-2) and methyl methanesulfonate (MMS) as well as spontaneous mutation in the reversion assay of E. coli WP2uvrA/pKM101. The effect was not, however, seen in the case of the mutagenesis induced by N-methyl-N′-nitro-N-nitrosoguanidine (MNNG).

In order to elucidate the mechanism of the mutation-inhibitory effect of sodium arsenite, its action on umuC gene expression and DNA-repair systems was investigated. It was found that sodium arsenite depressed β-galactosidase induction, corresponding to the umuC gene expression. For UV-irradiated E. coli strains possessing different DNA-repair capacities, sodium arsenite decreased the UV survival rates of WP2, WP2uvrA[uvrA] and WP67[uvrA polA], increased those of SOS-uninducible strains having either the recA⁺ or uvrA⁺ such as CM571 [recA], CM561 [lexA(Ind⁻)] and CM611[uvrA lexA (Ind⁻], and did not affect that of the uvrA recA double mutant, WP100.

From these results, we assume that sodium arsenite may have at least two roles in its antimutagenesis: as an inhibitor of umuC gene expression, and as an enhancer of the error-free repairs depending on the uvrA and recA genes.