The lipopolysaccharide of Brucella abortus BvrS/BvrR mutants contains lipid A modifications and has higher affinity for bactericidal cationic peptides.
The two-component BvrS/BvrR system is essential for Brucella abortus virulence. It was shown previously that its dysfunction abrogates expression of some major outer membrane proteins and increases bactericidal peptide sensitivity. Here, we report that BvrS/BvrR mutants have increased surface hydrophobicity and susceptibility to killing by nonimmune serum. The bvrS and bvrR mutant lipopolysaccharides (LPSs) bound more polymyxin B, chimeras constructed with bvrS mutant cells and parental LPS showed augmented polymyxin B resistance, and, conversely, parental cells and bvrS mutant LPS chimeras were more sensitive and displayed polymyxin B-characteristic outer membrane lesions, implicating LPS as being responsible for the phenotype of the BvrS/BvrR mutants. No qualitative or quantitative changes were detected in other envelope and outer membrane components examined: periplasmic beta(1-2) glucans, native hapten polysaccharide, and phospholipids. The LPS of the mutants was similar to parental LPS in O-polysaccharide polymerization and fine structure but showed both increased underacylated lipid A species and higher acyl-chain fluidity that correlated with polymyxin B binding. These lipid A changes did not alter LPS cytokine induction, showing that in contrast to other gram-negative pathogens, recognition by innate immune receptors is not decreased by these changes in LPS structure. Transcription of Brucella genes required for incorporating long acyl chains into lipid A (acpXL and lpxXL) or implicated in lipid A acylation control (bacA) was not affected. We propose that in Brucella the outer membrane homeostasis depends on the functioning of BvrS/BvrR. Accordingly, disruption of BvrS/BvrR damages the outer membrane, thus contributing to the severe attenuation manifested by bvrS and bvrR mutants.
Manterola
Lorea
L
Departamento de Microbiología y Parasitología, Universidad de Navarra, c/ Irunlarrea no. 1, 31008 Pamplona, Spain.
Moriyón
Ignacio
I
Moreno
Edgardo
E
Sola-Landa
Alberto
A
Weiss
David S
DS
Koch
Michel H J
MH
Howe
Jörg
J
Brandenburg
Klaus
K
López-Goñi
Ignacio
I
D000215:Acylation; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D002003:Brucella abortus / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D002006:Brucellosis / Q000276:immunology / Q000382:microbiology*; D016207:Cytokines / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006241:Haptens / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D007106:Immune Sera / Q000276:immunology; D008050:Lipid A / Q000378:metabolism*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D010641:Phenotype; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D014158:Transcription, Genetic; D014774:Virulence; D047071:beta-Glucans / Q000378:metabolism
D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; C471339:BvrR protein, Brucella; C471340:BvrS protein, Brucella; D016207:Cytokines; D006241:Haptens; D007106:Immune Sera; D008050:Lipid A; D010743:Phospholipids; D047071:beta-Glucans; C080135:cyclic beta(1-2)glucan