Nitric Oxide Metabolism and Resistance to Peroxynitrite by Neisseria Species

Thesis (Ph.D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Microbiology and Immunology, 2009.Neisseria gonorrhoeae is the causative agent of gonorrhea, a sexually transmitted disease that primarily infects the urogenital tract. Prolonged infection often leads to complications, such as disseminated gonococcal infection and pelvic inflammatory disease. Women specifically have high rates of asymptomatic disease that we believe are partially an effect of bacterial metabolism of nitric oxide, considering nitric oxide levels directly correlate with immune system state of activation. The central role of nitric oxide within the immune system involves not only its signaling properties, but also its toxic properties. My studies have focused on examining the ability of Neisseria species to both produce and degrade nitric oxide, while establishing a nitric oxide steady-state in the presence of nitrite or an exogenous source of nitric oxide, as well as its resistance to the toxic nitrogen species, nitric oxide and peroxynitrite. Both pathogenic and commensal Neisseria species were found to have similar enzymatic activities for the production and degradation of nitric oxide, in addition to being equally efficient at modulating nitric oxide levels from pro-inflammatory concentrations to non-inflammatory concentrations during denitrification. Auxotrophic strains requiring arginine, hypoxanthine, and uracil were found to establish unusually low nitric oxide steady-states in the presence of nitrite. These same strains have been correlated with causing asymptomatic infections in men, meaning that even in the presence of high levels of nitrite, nitric oxide levels would remain in the range where it is involved in establishing non-inflammatory conditions. Respiratory control was shown to have a direct influence on denitrification, causing changes to the nitric oxide steady-state level and the activities of nitrite reductase and nitric oxide reductase. The toxic properties of nitric oxide include additional direct and indirect effects as a result of generation of other reactive nitrogen species being generated, such as peroxynitrite. This strong oxidant represents a valuable means for the immune system to control and eradicate bacterial pathogens. N. gonorrhoeae was shown to have a high level of resistance to peroxynitrite, while N. meningitidis and E. coli showed high sensitivity to the reactive species. Mutational analysis of gonococcal orthologs to genes identified to be involved in nitrosative defense in other bacteria had no effect on peroxynitrite resistance in N. gonorrhoeae. This suggests that the gonococcus has redundant and/or unique mechanisms to survive the bactericidal effects of peroxynitrite that would allow for increased persistence of the pathogen