Differences in nitric oxide steady states between arginine, hypoxanthine, uracil auxotrophs (AHU) and non-AHU strains ofNeisseria gonorrhoeaeduring anaerobic respiration in the presence of nitrite

Abstract

Neisseria gonorrhoeae can grow by anaerobic respiration using nitrite as an alternative electron acceptor. Under these growth conditions, N. gonorrhoeae produces and degrades nitric oxide (NO), an important host defense molecule. Laboratory strain F62 has been shown to establish and maintain a NO steady-state level that is a function of the nitrite reductase/NO reductase ratio and is independent of cell number. The nitrite reductase activities (122–197 nmol NO2reduced·min–1·OD600–1) and NO reductase activities (88–155 nmol NO reduced·min–1·OD600–1) in a variety of gonococcal clinical isolates were similar to the specific activities seen in F62 (241 nmol NO2reduced·min–1·OD600–1and 88 nmol NO reduced·min–1·OD600–1, respectively). In seven gonococcal strains, the NO steady-state levels established in the presence of nitrite were similar to that of F62 (801–2121 nmol·L–1NO), while six of the strains, identified as arginine, hypoxanthine, and uracil auxotrophs (AHU), that cause asymptomatic infection in men had either two- to threefold (373–579 nmol·L–1NO) or about 100-fold (13–24 nmol·L–1NO) lower NO steady-state concentrations. All tested strains in the presence of a NO donor, 2,2′-(hydroxynitrosohydrazono)bis-ethanimine/NO, quickly lowered and maintained NO levels in the noninflammatory range of NO (<300 nmol·L–1). The generation of a NO steady-state concentration was directly affected by alterations in respiratory control in both F62 and an AHU strain, although differences in membrane function are suspected to be responsible for NO steady-state level differences in AHU strains.