Effects of DNA-damaging Agents on Aerobic Methylobacteria Capable and Incapable of Utilizing Dichloromethane

Methylobacterium dichloromethanicum DM4, a degrader of dichloromethane (DCM), was more tolerant to the effect of H₂O₂ and UV irradiation than Methylobacterium extorquens AM1, which does not consume DCM. The addition of CH₂Cl₂ to methylobacteria with active serine, ribulose monophosphate, and ribulose bisphosphate pathways of C₁ metabolism, grown on methanol, resulted in a 1.1- to 2.5-fold increase in the incorporation of α-³²P]dATP into DNA by the Klenow fragment (exo^?). Since DCM dehalogenase was not induced in this process, the increase in the total lengths of DNA gaps resulted from the action of DCM rather than S-chloromethylglutathione (intermediate of primary dehalogenation). The degree of DNA damage in the presence of CH₂Cl₂ was lower in DCM degraders than methylobacteria incapable of degrading this pollutant. This suggests that DCM degraders possess a more efficient mechanism of DNA repair.