title: Localization of penicillin-binding proteins to the splitting system of Staphylococcus aureus septa by using a mercury-penicillin V derivative.
abstract: Precise localization of penicillin-binding protein (PBP)-antibiotic complexes in a methicillin-sensitive Staphylococcus aureus strain (BB255), its isogenic heterogeneous methicillin-resistant transductant (BB270), and a homogeneous methicillin-resistant strain (Col) was investigated by high-resolution electron microscopy. A mercury-penicillin V (Hg-pen V) derivative was used as a heavy metal-labeled, electron-dense probe for accurately localizing PBPs in situ in single bacterial cells during growth. The most striking feature of thin sections was the presence of an abnormally large (17 to 24 nm in width) splitting system within the thick cross walls or septa of Hg-pen V-treated bacteria of all strains. Untreated control cells possessed a thin, condensed splitting system, 7 to 9 nm in width. A thick splitting system was also distinguishable in unstained thin sections, thereby confirming that the electron contrast of this structure was not attributed to binding of bulky heavy metal stains usually used for electron microscopy. Biochemical analyses demonstrated that Hg-pen V bound to isolated plasma membranes as well as sodium dodecyl sulfate-treated cell walls and that two or more PBPs in each strain bound to this antibiotic. In contrast, the splitting system in penicillin V-treated bacteria was rarely visible after 30 min in the presence of antibiotic. These findings suggest that while most PBPs were associated with the plasma membrane, a proportion of PBPs were located within the fabric of the cell wall, in particular, in the splitting system. Inhibition of one or more high-M(r) PBPs by beta-lactam antibiotics modified the splitting system and cross-wall structure, therefore supporting a role for these PBPs in the synthesis and architectural design of these structures in S. aureus.
authors.affiliation: Department of Microbiology, College of Biological Science, University of Guelph, Ontario, Canada.
authors.forename: T R
authors.initials: TR
authors.lastname: Paul
authors.forename: A
authors.initials: A
authors.lastname: Venter
authors.forename: L C
authors.initials: LC
authors.lastname: Blaszczak
authors.forename: T R
authors.initials: TR
authors.lastname: Parr
authors.forename: H
authors.initials: H
authors.lastname: Labischinski
authors.forename: T J
authors.initials: TJ
authors.lastname: Beveridge
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000302:isolation & purification*; D002451:Cell Compartmentation; D002455:Cell Division; D002473:Cell Wall / Q000648:ultrastructure*; D006602:Hexosyltransferases; D006651:Histocytochemistry / Q000379:methods; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D008854:Microscopy, Electron / Q000379:methods; D015335:Molecular Probes; D002267:Muramoylpentapeptide Carboxypeptidase / Q000302:isolation & purification*; D009941:Organomercury Compounds; D010404:Penicillin V / Q000031:analogs & derivatives*; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases; D013045:Species Specificity; D013194:Staining and Labeling / Q000379:methods*; D013211:Staphylococcus aureus / Q000254:growth & development / Q000648:ultrastructure*; D013347:Subcellular Fractions; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D015335:Molecular Probes; D009941:Organomercury Compounds; D046915:Penicillin-Binding Proteins; C075531:p-(chloromercuric)-phenoxyacetamido penicillin; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases; D010404:Penicillin V