title: Modulation of bacterial outer membrane vesicle production by envelope structure and content.
abstract: BACKGROUND
  Vesiculation is a ubiquitous secretion process of Gram-negative bacteria, where outer membrane vesicles (OMVs) are small spherical particles on the order of 50 to 250 nm composed of outer membrane (OM) and lumenal periplasmic content. Vesicle functions have been elucidated in some detail, showing their importance in virulence factor secretion, bacterial survival, and biofilm formation in pathogenesis. Furthermore, OMVs serve as an envelope stress response, protecting the secreting bacteria from internal protein misfolding stress, as well as external envelope stressors. Despite their important functional roles very little is known about the regulation and mechanism of vesicle production. Based on the envelope architecture and prior characterization of the hypervesiculation phenotypes for mutants lacking the lipoprotein, Lpp, which is involved in the covalent OM-peptidoglycan (PG) crosslinks, it is expected that an inverse relationship exists between OMV production and PG-crosslinked Lpp.
  
  
  RESULTS
  In this study, we found that subtle modifications of PG remodeling and crosslinking modulate OMV production, inversely correlating with bound Lpp levels. However, this inverse relationship was not found in strains in which OMV production is driven by an increase in "periplasmic pressure" resulting from the accumulation of protein, PG fragments, or lipopolysaccharide. In addition, the characterization of an nlpA deletion in backgrounds lacking either Lpp- or OmpA-mediated envelope crosslinks demonstrated a novel role for NlpA in envelope architecture.
  
  
  CONCLUSIONS
  From this work, we conclude that OMV production can be driven by distinct Lpp concentration-dependent and Lpp concentration-independent pathways.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, NC, 27710, USA. carmensch0311@gmail.com.
authors.forename: Carmen
authors.initials: C
authors.lastname: Schwechheimer
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, 27710, USA. Adam.Kulp@effem.com.
authors.forename: Adam
authors.initials: A
authors.lastname: Kulp
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, NC, 27710, USA. meta.kuehn@duke.edu.
authors.forename: Meta J
authors.initials: MJ
authors.lastname: Kuehn
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry*; D002473:Cell Wall / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry* / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D010457:Peptidoglycan / Q000378:metabolism; D011485:Protein Binding; D022142:Secretory Vesicles / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008074:Lipoproteins; C099932:Lpp protein, E coli; D010457:Peptidoglycan