A peptidoglycan hydrolase similar to bacteriophage endolysins acts as an autolysin in Neisseria gonorrhoeae

Abstract

SummaryWe have identified a gene encoding an autolysin (atlA) from Neisseria gonorrhoeae. The deduced amino acid sequence of AtlA shows significant similarity to the peptidoglycan degrading transglycosylases (endolysins) of bacteriophages lambda and P2, suggesting that the encoded protein also functions in peptidoglycan hydrolysis. An atlA mutant was identical to the wild-type strain in exponential growth rate, but demonstrated reduced lysis and peptidoglycan turnover in the stationary phase of growth. When transferred into a buffer solution, at a pH non-permissive for other gonococcal autolysins, an autolytic activity was detectable in the wild-type strain that was not present in the mutant. The most dramatic phenotype of the mutant occurred after extended time in stationary phase. After approximately 16 h in stationary phase, both strains underwent an apparent replication event, after which the wild-type strain died rapidly whereas the atlA mutant survived considerably longer. Even after both the wild-type and mutant cells were dead, many of the mutant cells maintained intact morphology, whereas the wild-type cells were lysed. These results suggest that AtlA is a peptidoglycan transglycosylase related to bacteriophage endolysins and acts as an autolysin in the stationary phase.

A Lytic Transglycosylase of Neisseria gonorrhoeae Is Involved in Peptidoglycan-Derived Cytotoxin Production

“…The viable counts decreased slowly, and at 50 h more than 10 5 CFU/ml survived. This phenotype is highly similar to that of an atlA mutant of N. gonorrhoeae MS11A (4).…”

AtlA Functions as a Peptidoglycan Lytic Transglycosylase in the Neisseria gonorrhoeae Type IV Secretion System

“…AtlA shows significant similarity to lambda R, the endolysin that breaks open E. coli during the lytic stage of lambda infection (6,14). This similarity suggested that AtlA might also be able to lyse bacterial cells.…”

“…The original studies with AtlA suggested that it might be an autolysin (14), but later studies identified a requirement of AtlA for DNA release during the growth phase. atlA insertion mutants had the same phenotype as other T4SS mutants, failing to donate DNA during coculture transformation and showing reduced release of DNA during growth (15,20).…”

“…These data indicate that the lytic PG transglycosylase activity of AtlA is required for type IV secretion. The main difference between AtlA and the related bacteriophage lytic transglycosylases is the presence of a 28-amino-acid extension on the N terminus of AtlA (14). We hypothesize that this region of the protein may be necessary for localization of AtlA to the T4SS or interaction with other T4SS proteins.…”

“…An insertion mutation in atlA eliminated detectable DNA in the culture supernatant and greatly reduced DNA donation for transformation (15). AtlA is similar to the bacteriophage lambda endolysin (lambda R) (14), an enzyme that digests peptidoglycan (PG) to break open Escherichia coli during the lytic stage of lambda infection in order to release phage particles (6,7). No other secretion system has been found to require an endolysin homologue for function.…”