title: Mutations of the Listeria monocytogenes peptidoglycan N-deacetylase and O-acetylase result in enhanced lysozyme sensitivity, bacteriolysis, and hyperinduction of innate immune pathways.
abstract: Listeria monocytogenes is a Gram-positive intracellular pathogen that is naturally resistant to lysozyme. Recently, it was shown that peptidoglycan modification by N-deacetylation or O-acetylation confers resistance to lysozyme in various Gram-positive bacteria, including L. monocytogenes. L. monocytogenes peptidoglycan is deacetylated by the action of N-acetylglucosamine deacetylase (Pgd) and acetylated by O-acetylmuramic acid transferase (Oat). We characterized Pgd(-), Oat(-), and double mutants to determine the specific role of L. monocytogenes peptidoglycan acetylation in conferring lysozyme sensitivity during infection of macrophages and mice. Pgd(-) and Pgd(-) Oat(-) double mutants were attenuated approximately 2 and 3.5 logs, respectively, in vivo. In bone-marrow derived macrophages, the mutants demonstrated intracellular growth defects and increased induction of cytokine transcriptional responses that emanated from a phagosome and the cytosol. Lysozyme-sensitive mutants underwent bacteriolysis in the macrophage cytosol, resulting in AIM2-dependent pyroptosis. Each of the in vitro phenotypes was rescued upon infection of LysM(-) macrophages. The addition of extracellular lysozyme to LysM(-) macrophages restored cytokine induction, host cell death, and L. monocytogenes growth inhibition. This surprising observation suggests that extracellular lysozyme can access the macrophage cytosol and act on intracellular lysozyme-sensitive bacteria.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3202, USA.
authors.forename: Chris S
authors.initials: CS
authors.lastname: Rae
authors.forename: Aimee
authors.initials: A
authors.lastname: Geissler
authors.forename: Paul C
authors.initials: PC
authors.lastname: Adamson
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Portnoy
mesh_terms: D000107:Acetylation; D000581:Amidohydrolases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D001433:Bacteriolysis; D016207:Cytokines / Q000096:biosynthesis; D005260:Female; D007113:Immunity, Innate; D008089:Listeria monocytogenes / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000276:immunology*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009113:Muramidase / Q000378:metabolism*; D009154:Mutation; D010457:Peptidoglycan / Q000276:immunology / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014166:Transferases / Q000235:genetics / Q000378:metabolism*
chemical_list: D016207:Cytokines; D010457:Peptidoglycan; D034741:RNA, Small Interfering; D014166:Transferases; D009113:Muramidase; D000581:Amidohydrolases; C023079:N-acetylglucosamine deacetylase