Hydrogen peroxide induces protection against N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) effects in Escherichia coli

Abstract Cross-adaptive response is defined as the capacity of cells to become resistant to a lethal agent when pretreated with a different lethal substance. In the present paper, the cross-adaptive response between hydrogen peroxide and N -methyl- N ′-nitro- N -nitrosoguanidine (MNNG) was studied in Escherichia coli repair mutants. Our results suggest that high doses of H 2 O 2 induces protection against the lethal effects of MNNG in wild-type strain, ada , ogt , ada-ogt , aidB and alkA mutants. On the other hand, the MNNG induced mutagenesis is reduced by H 2 O 2 pretreatment in wild-type and ogt mutant strains, but not in ada mutant. Furthermore, the protecting effect induced by H 2 O 2 is time dependent: it decreases 15 min after the pretreatment and, after 30 min, is almost abolished. This reduction in the protecting effect is followed by an augmentation in the mutation frequency when MNNG is added 30 min after H 2 O 2 pretreatment. This cross-adaptive response may be due to a modification of the MNNG alkylation pattern in the oxidized DNA.