title: Extensive cell envelope modulation is associated with virulence in Brucella abortus.
abstract: Brucella virulence is linked to components of the cell envelope and tightly connected to the function of the BvrR/BvrS sensory-regulatory system. To quantify the impact of BvrR/BvrS on cell envelope proteins, we performed a label-free mass spectrometry-based proteomic analysis of spontaneously released outer membrane fragments from four strains of Brucella abortus (wild type virulent, avirulent bvrR- and bvrS- mutants as well as reconstituted virulent bvrR+ (bvrR-/pbvrR+)). We identified 167 differentially expressed proteins, of which 25 were assigned to the outer membrane. Approximately half of the outer membrane proteins decreased in abundance, whereas half increased. Notably, expression of five Omp3 family proteins decreased whereas five lipoproteins increased in the mutant strains. In the periplasmic space, by contrast, approximately 80% of the 60 differentially expressed proteins were increased in at least one avirulent mutant. Periplasmic proteins are primarily involved in substrate uptake and transport, and a uniform increase in this class may indicate a nutritional stress response, possibly a consequence of defective outer membrane function. Virtually all proteins reverted to wild type levels in the reconstituted virulent bvrR+ strain. We propose that the wide changes in cell envelope protein expression relate to the markedly avirulent phenotype of bvrR- and bvrS- mutants and that Brucella virulence depends on regulatory networks involving cell envelope and metabolism rather than on discrete virulence factors. This model may be relevant to other alpha-Proteobacteria harboring BvrR/BvrS orthologous systems known to be essential for parasitism or endosymbiosis.
authors.affiliation: Caprion Pharmaceuticals, 7150 Alexander-Fleming, Montreal, Quebec, Canada H4S 2C8.
authors.forename: Julie
authors.initials: J
authors.lastname: Lamontagne
authors.forename: Heather
authors.initials: H
authors.lastname: Butler
authors.forename: Esteban
authors.initials: E
authors.lastname: Chaves-Olarte
authors.forename: Joanna
authors.initials: J
authors.lastname: Hunter
authors.forename: Michael
authors.initials: M
authors.lastname: Schirm
authors.forename: Caroline
authors.initials: C
authors.lastname: Paquet
authors.forename: Mei
authors.initials: M
authors.lastname: Tian
authors.forename: Paul
authors.initials: P
authors.lastname: Kearney
authors.forename: Lyes
authors.initials: L
authors.lastname: Hamaidi
authors.forename: Daniel
authors.initials: D
authors.lastname: Chelsky
authors.forename: Ignacio
authors.initials: I
authors.lastname: Moriyón
authors.forename: Edgardo
authors.initials: E
authors.lastname: Moreno
authors.forename: Eustache
authors.initials: E
authors.lastname: Paramithiotis
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis* / Q000378:metabolism; D002003:Brucella abortus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D033903:Periplasmic Proteins / Q000032:analysis* / Q000378:metabolism; D018272:Porins / Q000032:analysis* / Q000378:metabolism; D014774:Virulence
chemical_list: D001425:Bacterial Outer Membrane Proteins; D033903:Periplasmic Proteins; D018272:Porins