The role of catalase in gonococcal resistance to peroxynitrite

We have reported that Neisseria gonorrhoeae is extremely resistant to reactive nitrogen species (RNS) including peroxynitrite (PN). Recent literature suggests that catalase can provide protection against commercial preparations of PN. Though wild-type gonococci were shown to be highly resistant to 2 mM PN, Neisseria meningitidis and a gonococcal katA mutant were both shown to be extremely sensitive to 2 mM PN. Analysis of translational fusions to lacZ of the catalase promoters from N. gonorrhoeae and N. meningitidis demonstrated that basal katA expression from gonococci is 80-fold higher than in meningococci, though meningococcal katA retains a greater capacity to be activated by OxyR. This activation capacity was shown to be due to a single base pair difference in the -10 transcription element between the two kat promoters. PN resistance was initially shown to be associated with increasing catalase expression; however, commercial preparations of PN were later revealed to contain higher levels of contaminating hydrogen peroxide (H2O2) than expected. Removal of H2O2 from PN preparations with manganese dioxide markedly reduced PN toxicity in a gonococcal katA mutant. Simultaneous treatment with non-lethal concentrations of PN and H2O2 was highly lethal, indicating that these agents act synergistically. When treatment was separated by 5 min, high levels of bacterial killing occurred only when PN was added first. Our results suggest that killing of N. gonorrhoeae ΔkatA by commercial PN preparations is likely due to H2O2, that H2O2 is more toxic in the presence of PN, and that PN, on its own, may not be as toxic as previously believed.