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Mutations in ampG or ampD affect peptidoglycan fragment release from Neisseria gonorrhoeae.

ABSTRACT: Neisseria gonorrhoeae releases peptidoglycan fragments during growth. The majority of the fragments released are peptidoglycan monomers, molecules known to increase pathogenesis through the induction of proinflammatory cytokines and responsible for the killing of ciliated epithelial cells. In other gram-negative bacteria such as Escherichia coli, these peptidoglycan fragments are efficiently degraded and recycled. Peptidoglycan fragments enter the cytoplasm from the periplasm via the AmpG permease. The amidase AmpD degrades peptidoglycan monomers by removing the disaccharide from the peptide. The disaccharide and the peptide are further degraded and are then used for new peptidoglycan synthesis or general metabolism. We examined the possibility that peptidoglycan fragment release by N. gonorrhoeae results from defects in peptidoglycan recycling. The deletion of ampG caused a large increase in peptidoglycan monomer release. Analysis of cytoplasmic material showed peptidoglycan fragments as recycling intermediates in the wild-type strain but absent from the ampG mutant. An ampD deletion reduced the release of all peptidoglycan fragments and nearly eliminated the release of free disaccharide. The ampD mutant also showed a large buildup of peptidoglycan monomers in the cytoplasm. The introduction of an ampG mutation in the ampD background restored peptidoglycan fragment release, indicating that events in the cytoplasm (metabolic or transcriptional regulation) affect peptidoglycan fragment release. The ampD mutant showed increased metabolism of exogenously added free disaccharide derived from peptidoglycan. These results demonstrate that N. gonorrhoeae has an active peptidoglycan recycling pathway and can regulate peptidoglycan fragment metabolism, dependent on the intracellular concentration of peptidoglycan fragments.

SUBMITTER: Garcia DL

PROVIDER: S-EPMC2395056 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature

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Mutations in ampG or ampD affect peptidoglycan fragment release from Neisseria gonorrhoeae.

Garcia Daniel L DL Dillard Joseph P JP

Journal of bacteriology 20080404 11

Neisseria gonorrhoeae releases peptidoglycan fragments during growth. The majority of the fragments released are peptidoglycan monomers, molecules known to increase pathogenesis through the induction of proinflammatory cytokines and responsible for the killing of ciliated epithelial cells. In other gram-negative bacteria such as Escherichia coli, these peptidoglycan fragments are efficiently degraded and recycled. Peptidoglycan fragments enter the cytoplasm from the periplasm via the AmpG permea ...[more]

PMID: 18390650

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Project description:Neisseria gonorrhoeae (gonococci) and Neisseria meningitidis (meningococci) are human pathogens that cause gonorrhea and meningococcal meningitis, respectively. Both N. gonorrhoeae and N. meningitidis release a number of small peptidoglycan (PG) fragments, including proinflammatory PG monomers, although N. meningitidis releases fewer PG monomers. The PG fragments released by N. gonorrhoeae and N. meningitidis are generated in the periplasm during cell wall remodeling, and a majority of these fragments are transported into the cytoplasm by an inner membrane permease, AmpG; however, a portion of the PG fragments are released into the extracellular environment through unknown mechanisms. We previously reported that the expression of meningococcal ampG in N. gonorrhoeae reduced PG monomer release by gonococci. This finding suggested that the efficiency of AmpG-mediated PG fragment recycling regulates the amount of PG fragments released into the extracellular milieu. We determined that three AmpG residues near the C-terminal end of the protein modulate AmpG's efficiency. We also investigated the association between PG fragment recycling and release in two species of human-associated nonpathogenic Neisseria: N. sicca and N. mucosa Both N. sicca and N. mucosa release lower levels of PG fragments and are more efficient at recycling PG fragments than N. gonorrhoeae Our results suggest that N. gonorrhoeae has evolved to increase the amounts of toxic PG fragments released by reducing its PG recycling efficiency.Neisseria gonorrhoeae and Neisseria meningitidis are human pathogens that cause highly inflammatory diseases, although N. meningitidis is also frequently found as a normal member of the nasopharyngeal microbiota. Nonpathogenic Neisseria, such as N. sicca and N. mucosa, also colonize the nasopharynx without causing disease. Although all four species release peptidoglycan fragments, N. gonorrhoeae is the least efficient at recycling and releases the largest amount of proinflammatory peptidoglycan monomers, partly due to differences in the recycling permease AmpG. Studying the interplay between bacterial physiology (peptidoglycan metabolism) and pathogenesis (release of toxic monomers) leads to an increased understanding of how different bacterial species maintain asymptomatic colonization or cause disease and may contribute to efforts to mitigate disease.

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Mutations in ampG or ampD affect peptidoglycan fragment release from Neisseria gonorrhoeae.

Publications

Mutations in ampG or ampD affect peptidoglycan fragment release from Neisseria gonorrhoeae.

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