Abstract
Neisseria gonorrhoeae survives anaerobically by reducing nitrite to nitrous oxide catalyzed by the nitrite and nitric oxide reductases, AniA and NorB. P(aniA) is activated by FNR (regulator of fumarate and nitrate reduction), the two-component regulatory system NarQ-NarP, and induced by nitrite; P(norB) is induced by NO independently of FNR by an uncharacterized mechanism. We report the results of microarray analysis, bioinformatic analysis, and chromatin immunoprecipitation, which revealed that only five genes with readily identified NarP-binding sites are differentially expressed in narP(+) and narP strains. These include three genes implicated in the truncated gonococcal denitrification pathway: aniA, norB, and narQ. We also report that (i) nitrite induces aniA transcription in a narP mutant; (ii) nitrite induction involves indirect inactivation by nitric oxide of a gonococcal repressor, NsrR, identified from a multigenome bioinformatic study; (iii) in an nsrR mutant, aniA, norB, and dnrN (encoding a putative reactive nitrogen species response protein) were expressed constitutively in the absence of nitrite, suggesting that NsrR is the only NO-sensing transcription factor in N. gonorrhoeae; and (iv) NO rather than nitrite is the ligand to which NsrR responds. When expressed in Escherichia coli, gonococcal NarQ and chimaeras of E. coli and gonococcal NarQ are ligand-insensitive and constitutively active: a "locked-on" phenotype. We conclude that genes involved in the truncated denitrification pathway of N. gonorrhoeae are key components of the small NarQP regulon, that NarP indirectly regulates P(norB) by stimulating NO production by AniA, and that NsrR plays a critical role in enabling gonococci to evade NO generated as a host defense mechanism.
Highlights
We report the results of microarray analysis, bioinformatic analysis, and chromatin immunoprecipitation, which revealed that only five genes with readily identified NarP-binding sites are differentially expressed in narP؉ and narP strains
We report that (i) nitrite induces aniA transcription in a narP mutant; (ii) nitrite induction involves indirect inactivation by nitric oxide of a gonococcal repressor, NsrR, identified from a multigenome bioinformatic study; (iii) in an nsrR mutant, aniA, norB, and dnrN were expressed constitutively in the absence of nitrite, suggesting that NsrR is the only NO-sensing transcription factor in N. gonorrhoeae; and (iv) NO rather than nitrite is the ligand to which NsrR responds
In contrast to Escherichia coli that can inhabit a variety of environments and utilize numerous carbon sources and electron acceptors, some niche dwellers such as the obligate human pathogen Neisseria gonorrhoeae are far less versatile
Summary
This work This work This work This work response to the availability of reactive nitrogen species, regulate expression of genes involved in denitrification and reactive nitrogen species metabolism [10, 11]. A multigenome bioinformatic study identified a putative Rrf family member similar in sequence to the NsrR proteins of E. coli and Nitrosomonas europea in N. gonorrhoeae [12]. The same study identified putative NsrR binding sites in the aniA promoter region (Fig. 1B) and in the regulatory regions of three other genes that include norB and dnrN (NGO0653), which is predicted to encode a reactive nitrogen species-responsive protein. We have investigated the roles of NarQ-NarP and NsrR (NGO1519) in the regulation of the truncated denitrification pathway of the gonococcus. We show that the gonococcal NarQ is insensitive to nitrite and apparently locked on in its sensor kinase mode
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