Breaking down the wall: Peptidoglycan degradation enzymes affect infection, inflammation, and cell separation in Neisseria gonorrhoeae

Neisseria gonorrhoeae is a gram-negative bacterial pathogen that is the causative agent of the sexually-transmitted infection gonorrhea as well as damaging sequellae including pelvic inflammatory disease, epididymitis, septicemia, and meningitis. The bacteria do not make any classical toxins, but rather it is the immune response to bacterial cell constituents that results in pathology. During infection of human Fallopian tubes, immune responses to gonococcal peptidoglycan and lipooligosaccharide result in the death of ciliated cells and tissue damage causing tubal factor infertility. N. gonorrhoeae releases significant amounts of peptidoglycan monomers as the bacteria grow and divide. We are investigating the mechanisms involved in production and release of the toxic peptidoglycan fragments, and we are characterizing the lytic transglycosylases, amidases, endopeptidases, carboxypeptidases, and a permease involved in peptidoglycan recycling or release. These studies have demonstrated differences in the gonococcal enzymes compared to those of non-pathogens or model organisms and suggest that substrate specificity and enzyme localization favor increased peptidoglycan fragment release. In the course of studying peptidoglycan fragment production, we have identified enzymes required for cell separation. Mutations affecting cell separation cause the bacteria to grow as two or more, four or more, or as many as 20 bacteria per group surrounded by a single, unstable outer membrane. These mutants show increased sensitivity to antibiotics and chaotropic agents, suggesting that cell separation is a promising target for new antimicrobials.