Accumulation of manganese in Neisseria gonorrhoeae correlates with resistance to oxidative killing by superoxide anion and is independent of superoxide dismutase activity

As a facultative aerobe with a high iron requirement and a highly active ae robic respiratory chain, Neisseria gonorrhoeae requires defence systems to respond to toxic oxygen species such as superoxide. It has been shown that supplementation of media with 100 muM Mn(II) considerably enhanced the resi stance of this bacterium to oxidative killing by superoxide. This protectio n was not associated with the superoxide dismutase enzymes of N. gonorrhoea e. In contrast to previous studies, which suggested that some strains of N. gonorrhoeae might not contain a superoxide dismutase, we identified a sodB gene by genome analysis and confirmed its presence in all strains examined by Southern blotting, but found no evidence for sodA or sodC. A sodB mutan t showed very similar susceptibility to superoxide killing to that of wild- type cells, indicating that the Fe-dependent SOD B did not have a major rol e in resistance to oxidative killing under the conditions tested. The absen ce of a sodA gene indicated that the Mn-dependent protection against oxidat ive killing was independent of Mn-dependent SOD A. As a sodB mutant also sh owed Mn-dependent resistance to oxidative killing, then it is concluded tha t this resistance is independent of superoxide dismutase enzymes. Resistanc e to oxidative killing was correlated with accumulation of Mn(II) by the ba cterium. We hypothesize that this bacterium uses Mn(II) as a chemical quenc hing agent in a similar way to the already established process in Lactobaci llus plantarum. A search for putative Mn(II) uptake systems identified an A BC cassette-type system (MntABC) with a periplasmic-binding protein (MntC). An mntC mutant was shown to have lowered accumulation of Mn(II) and was al so highly susceptible to oxidative killing, even in the presence of added M n(II). Taken together, these data show that N. gonorrhoeae possesses a Mn(I I) uptake system that is critical for resistance to oxidative stress.