The transcriptome response of Neisseria gonorrhoeae to hydrogen peroxide reveals genes with previously uncharacterized roles in oxidative damage protection

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Abstract
Symptomatic gonococcal infection, caused by the pathogen Neisseria gonorrhoeae (Gc), is characterized by the influx of polymorphonuclear leukocytes (PMNs) to the site of infection. Although PMNs possess several mechanisms of oxidative killing, intact Gc can be found associated with PMNs, suggesting that gonococcal defences against oxidative stress are crucial for its ability to evade killing by PMNs. We used microarrays to identify genes that were differentially expressed after transient exposure of Gc to hydrogen peroxide (H2O2). Of the 75 genes found to be upregulated after H2O2 treatment, over one-quarter, including two of the most highly upregulated genes (NGO1686 and NGO554), were predicted to encode proteins with unknown functions. Further characterization of a subset of these upregulated genes demonstrated that NGO1686, a putative zinc metalloprotease, protects against oxidative damage caused by both H2O2 and cumene hydroperoxide, and that NGO554, a Gc-specific protein, acts to protect against damage caused by high levels of H2O2. Our current study also ascribes a role in H2O2 damage protection to recN, a gene previously characterized for its role in DNA repair. A PMN survival assay demonstrated that the recN and NGO1686 mutants were more susceptible to killing than the parent strain FA1090. These results define for the first time the robust transcriptional response to H2O2 by this strict human pathogen and underscore the importance of this system for survival to host defences.