Neisseria gonorrhoeae is prone to undergo
autolysis under many conditions not conducive to growth. The role of
autolysis during gonococcal
infection is not known, but possible advantages for the bacterial population include provision of nutrients to a starving population, modulation of the host immune response by released cell components, and donation of
DNA for natural transformation. Biochemical studies indicated that an N-acetylmuramyl-
l-alanine amidase is responsible for cell wall breakdown during
autolysis. In order to better understand
autolysis and in hopes of creating a nonautolytic mutant, we mutated amiC, the gene for a putative
peptidoglycan-degrading
amidase in N. gonorrhoeae. Characterization of
peptidoglycan fragments released during growth showed that an amiC mutant did not produce free
disaccharide, consistent with a role for AmiC as an N-acetylmuramyl-
l-alanine amidase. Compared to the wild-type parent, the mutant exhibited altered growth characteristics, including slowed exponential-phase growth, increased turbidity in stationary phase, and increased colony opacity. Thin-section electron micrographs showed that mutant cells did not fully separate but grew as clumps. Complementation of the amiC deletion mutant with wild-type amiC restored wild-type growth characteristics and transparent colony morphology. Overexpression of amiC resulted in increased cell lysis, supporting AmiC's purported function as a gonococcal
autolysin. However, amiC mutants still underwent
autolysis in stationary phase, indicating that other gonococcal
enzymes are also involved in this process.