Is N₂O-dependent Damage ‘Fixed’ by Action of the recA Locus?

Summary

Nitrous oxide (N₂O) is often a radiation sensitizer of procaryotic cells, although it has little or no effect in recA⁻ strains of E. coli and Saccharomyces. Here we test the hypothesis that N₂O-dependent damage is in itself not lethal, but that lethality occurs when this damage is incorrectly repaired by the recA⁺ strains. Because sensitization by N₂O requires the radiolytic production of H₂O₂, the hypothesis can be tested with reagent H₂O₂. If the ‘inaction’ of the recA locus prevents N₂O sensitization in the recA⁻ strains, then those strains should not be sensitized by reagent H₂O₂. Our data show that all these strains, including the recA⁺ parent, are efficiently sensitized by reagent H₂O₂ in N₂ and also in N₂O; thus our data do not support that hypothesis. We propose instead that the correlation between N₂O sensitization and the recA⁻ genotype occurs because of the inherent anoxic sensitivity of the recA⁻ strains; the doses used to assay survival, and thus to test for sensitization by N₂O, are simply too low to produce sufficient H₂O₂ for sensitization to occur.