Characterization of the gonococcal genetic island and peptidoglycan fragment release in Neisseria meningitidis

This dissertation describes detailed characterization of the gonococcal genetic island (GGI) and its encoded type IV secretion system (T4SS) as well as peptidoglycan fragment release by Neisseria meningitidis (meningococcus). The GGI was first found in N. gonorrhoeae (gonococcus). We screened 126 N. meningitidis isolates and found that 20% of strains carry the GGI. We identified five distinct GGI types in meningococci, two of which have similar T4SS-encoding regions to gonococci. Unlike the gonococcal T4SS, the meningococcal T4SS was not found to secrete DNA. The meningococcal GGI also has no effect on adherence, invasion, or iron uptake for intracellular survival, in cervical epithelial cells. Despite genetic similarities between the GGI in N. gonorrhoeae and N. meningitidis, the function of the GGI in meningococci remains unclear.;Previous work showed that purified meningococcal peptidoglycan activates NF-κB through Nod1. We hypothesized that meningococci release peptidoglycan fragments during growth that induce an inflammatory response through Nod1. We observed meningococcal release of peptidoglycan dimers, monomers, free disaccharide, and two free peptide fragments. Recycling of peptidoglycan monomers was highly efficient (96%), which is more efficient than recycling in gonococci. Comparison of peptidoglycan fragment release by N. meningitidis and N. gonorrhoeae revealed that meningococci release less of the pro-inflammatory monomer and release additional, smaller dimer and monomer fragments. These data suggest that meningococci alter peptidoglycan fragment release by increasing recycling efficiency and degrading peptidoglycan fragments further. The variations in fragment release between the pathogenic Neisseria results in significantly less Nod1-dependent NF-κB activation by meningococcal supernatants. Decreasing inflammatory peptidoglycan release may be advantageous for N. meningitidis to maintain colonization of its human host.;Meningococci were found to release two different free peptide fragments from the cell wall, and required the proteins AmiC and NlpD for this process. AmiC is an amidase that cleaves the bond between N-acetylmuramic acid and L-alanine and is required for cell separation. The putative endopeptidase NlpD was also required for cell separation. Mutation of amiC or nlpD had different effects on the release of peptidoglycan fragments. It is not clear whether NlpD enhances activity of AmiC, or if NlpD itself is capable of peptidoglycan degradation.