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Elhenawy W, Bording-Jorgensen M, Valguarnera E, Haurat MF, Wine E, Feldman MF. LPS Remodeling Triggers Formation of Outer Membrane Vesicles in Salmonella. mBio 2016; 7:e00940-16. [PMID: 27406567 PMCID: PMC4958258 DOI: 10.1128/mbio.00940-16] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 06/09/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Outer membrane vesicles (OMV) are proposed to mediate multiple functions during pathogenesis and symbiosis. However, the mechanisms responsible for OMV formation remain poorly understood. It has been shown in eukaryotic membranes that lipids with an inverted-cone shape favor the formation of positive membrane curvatures. Based on these studies, we formulated the hypothesis that lipid A deacylation might impose shape modifications that result in the curvature of the outer membrane (OM) and subsequent OMV formation. We tested the effect of lipid A remodeling on OMV biogenesis employing Salmonella enterica serovar Typhimurium as a model organism. Expression of the lipid A deacylase PagL resulted in increased vesiculation, without inducing an envelope stress response. Mass spectrometry analysis revealed profound differences in the patterns of lipid A in OM and OMV, with accumulation of deacylated lipid A forms exclusively in OMV. OMV biogenesis by intracellular bacteria upon macrophage infection was drastically reduced in a pagL mutant strain. We propose a novel mechanism for OMV biogenesis requiring lipid A deacylation in the context of a multifactorial process that involves the orchestrated remodeling of the outer membrane. IMPORTANCE The role of lipid remodeling in vesiculation is well documented in eukaryotes. Similarly, bacteria produce membrane-derived vesicles; however, the molecular mechanisms underlying their production are yet to be determined. In this work, we investigated the role of outer membrane remodeling in OMV biogenesis in S Typhimurium. We showed that the expression of the lipid A deacylase PagL results in overvesiculation with deacylated lipid A accumulation exclusively in OMV. An S Typhimurium ΔpagL strain showed a significant reduction in intracellular OMV secretion relative to the wild-type strain. Our results suggest a novel mechanism for OMV biogenesis that involves outer membrane remodeling through lipid A modification. Understanding how OMV are produced by bacteria is important to advance our understanding of the host-pathogen interactions.
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Affiliation(s)
- Wael Elhenawy
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | | | - Ezequiel Valguarnera
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, St. Louis, Missouri, USA
| | - M Florencia Haurat
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Eytan Wine
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Mario F Feldman
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, St. Louis, Missouri, USA
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Bi CL, Wang H, Wang YJ, Sun J, Dong JS, Meng X, Li JJ. Selenium inhibits Staphylococcus aureus-induced inflammation by suppressing the activation of the NF-κB and MAPK signalling pathways in RAW264.7 macrophages. Eur J Pharmacol 2016; 780:159-65. [DOI: 10.1016/j.ejphar.2016.03.044] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 03/18/2016] [Accepted: 03/24/2016] [Indexed: 12/25/2022]
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Román BS, Garrido V, Muñoz PM, Arribillaga L, García B, De Andrés X, Zabaleta V, Mansilla C, Farrán I, Lasa I, De Andrés D, Amorena B, Lasarte JJ, Grilló MJ. The extradomain a of fibronectin enhances the efficacy of lipopolysaccharide defective Salmonella bacterins as vaccines in mice. Vet Res 2012; 43:31. [PMID: 22515195 PMCID: PMC3418186 DOI: 10.1186/1297-9716-43-31] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 03/29/2012] [Indexed: 12/12/2022] Open
Abstract
The Extradomain A from fibronectin (EDA) has an immunomodulatory role as fusion protein with viral and tumor antigens, but its effect when administered with bacteria has not been assessed. Here, we investigated the adjuvant effect of EDA in mice immunizations against Salmonella enterica subspecies enterica serovar Enteritidis (Salmonella Enteritidis). Since lipopolysaccharide (LPS) is a major virulence factor and the LPS O-polysaccharide (O-PS) is the immunodominant antigen in serological diagnostic tests, Salmonella mutants lacking O-PS (rough mutants) represent an interesting approach for developing new vaccines and diagnostic tests to differentiate infected and vaccinated animals (DIVA tests). Here, antigenic preparations (hot-saline extracts and formalin-inactivated bacterins) from two Salmonella Enteritidis rough mutants, carrying either intact (SEΔwaaL) or deep-defective (SEΔgal) LPS-Core, were used in combination with EDA. Biotinylated bacterins, in particular SEΔwaaL bacterin, decorated with EDAvidin (EDA and streptavidin fusion protein) improved the protection conferred by hot-saline or bacterins alone and prevented significantly the virulent infection at least to the levels of live attenuated rough mutants. These findings demonstrate the adjuvant effect of EDAvidin when administered with biotinylated bacterins from Salmonella Enteritidis lacking O-PS and the usefulness of BEDA-SEΔwaaL as non-live vaccine in the mouse model.
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Affiliation(s)
- Beatriz San Román
- Instituto de Agrobiotecnología (CSIC-UPNA-Gobierno de Navarra), Carretera de Mutilva, s/n, 31192 Pamplona, Spain.
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Abstract
The mammalian innate immune response provides a barrier against invading pathogens. Innate immune mechanisms are used by the host to respond to a range of bacterial pathogens in an acute and conserved fashion. Host cells express pattern recognition receptors that sense pathogen-associated molecular patterns. After detection, an arsenal of antimicrobial mechanisms is deployed to kill bacteria in infected cells. Innate immunity also stimulates antigen-specific responses mediated by the adaptive immune system. In response, pathogens manipulate host defence mechanisms to survive and eventually replicate. This Review focuses on the control of host innate immune responses by pathogenic intracellular bacteria.
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Effect of the O-antigen length of lipopolysaccharide on the functions of Type III secretion systems in Salmonella enterica. Infect Immun 2009; 77:5458-70. [PMID: 19797066 DOI: 10.1128/iai.00871-09] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The virulence of Salmonella enterica critically depends on the functions of two type III secretion systems (T3SS), with the Salmonella pathogenicity island 1 (SPI1)-encoded T3SS required for host cell invasion and the SPI2-T3SS enabling Salmonella to proliferate within host cells. A further T3SS is required for the assembly of the flagella. Most serovars of Salmonella also possess a lipopolysaccharide with a complex O-antigen (OAg) structure. The number of OAg units attached to the core polysaccharide varies between 16 and more than 100 repeats, with a trimodal distribution. This work investigated the correlation of the OAg length with the functions of the SPI1-T3SS and the SPI2-T3SS. We observed that the number of repeats of OAg units had no effect on bacterial motility. The interaction of Salmonella with epithelial cells was altered if the OAg structure was changed by mutations in regulators of OAg. Strains defective in synthesis of very long or long and very long OAg species showed increased translocation of a SPI1-T3SS effector protein and increased invasion. Invasion of a strain entirely lacking OAg was increased, but this mutant strain also showed increased adhesion. In contrast, translocation of a SPI2-T3SS effector protein and intracellular replication were not affected by modification of the OAg length. Mutant strains lacking the entire OAg or long and very long OAg were highly susceptible to complement killing. These observations indicate that the architecture of the outer membrane of Salmonella is balanced to permit sufficient T3SS function but also to confer optimal protection against antimicrobial defense mechanisms.
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Paterson GK, Cone DB, Peters SE, Maskell DJ. The enzyme phosphoglucomutase (Pgm) is required by Salmonella enterica serovar Typhimurium for O-antigen production, resistance to antimicrobial peptides and in vivo fitness. MICROBIOLOGY-SGM 2009; 155:3403-3410. [PMID: 19589833 DOI: 10.1099/mic.0.029553-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The enzyme phosphoglucomutase (Pgm) catalyses the interconversion of glucose 1-phosphate and glucose 6-phosphate and contributes to glycolysis and the generation of sugar nucleotides for biosynthesis. To assess the role of this enzyme in the biology of the pathogen Salmonella enterica serovar Typhimurium we have characterized a pgm deletion mutant in strain SL1344. Compared to SL1344, SL1344 pgm had impaired growth in vitro, was deficient in the ability to utilize galactose as a carbon source and displayed reduced O-antigen polymer length. The mutant was also more susceptible to antimicrobial peptides and showed decreased fitness in the mouse typhoid model. The in vivo phenotype of SL1344 pgm indicated a role for pgm in the early stages of infection, most likely through deficient O-antigen production. Although pgm mutants in other pathogens have potential as live attenuated vaccine strains, SL1344 pgm was not sufficiently attenuated for such use.
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Affiliation(s)
- G K Paterson
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - D B Cone
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - S E Peters
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
| | - D J Maskell
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
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Omeprazole antagonizes virulence and inflammation in Salmonella enterica-infected RAW264.7 cells. Antimicrob Agents Chemother 2009; 53:2402-9. [PMID: 19307359 DOI: 10.1128/aac.01483-08] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The proton pump inhibitor omeprazole reduced the intracellular replication of Salmonella enterica serovar Typhimurium in RAW264.7 cells without affecting bacterial growth in vitro or the viability of the host cells. The mechanism was bacteriostatic and interfered with replication mediated by the virulence-associated SPI2 type III secretion system. The proton pump inhibitor bafilomycin A(1), in contrast, mediated killing of intracellular bacteria and imposed a marked cytotoxicity on RAW264.7 cells. The two compounds also differentially affected the proinflammatory responses of the infected cells. Bafilomycin A(1) enhanced nitric oxide production, whereas omeprazole delayed IkappaB degradation and blocked nitric oxide production and the secretion of proinflammatory cytokines. These results imply that omeprazole can be used to block the virulence factor-mediated intracellular replication of S. Typhimurium, and that its mechanism of growth inhibition is different from that mediated by bafilomycin A(1).
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Negrea A, Bjur E, Ygberg SE, Elofsson M, Wolf-Watz H, Rhen M. Salicylidene acylhydrazides that affect type III protein secretion in Salmonella enterica serovar typhimurium. Antimicrob Agents Chemother 2007; 51:2867-76. [PMID: 17548496 PMCID: PMC1932493 DOI: 10.1128/aac.00223-07] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A collection of nine salicylidene acylhydrazide compounds were tested for their ability to inhibit the activity of virulence-associated type III secretion systems (T3SSs) in Salmonella enterica serovar Typhimurium. The compounds strongly affected Salmonella pathogenicity island 1 (SPI1) T3SS-mediated invasion of epithelial cells and in vitro secretion of SPI1 invasion-associated effector proteins. The use of a SPI1 effector beta-lactamase fusion protein implicated intracellular entrapment of the protein construct upon application of a salicylidene acylhydrazide, whereas the use of chromosomal transcriptional gene fusions revealed a compound-mediated transcriptional silencing of SPI1. Salicylidene acylhydrazides also affected intracellular bacterial replication in murine macrophage-like cells and blocked the transport of an epitope-tagged SPI2 effector protein. Two of the compounds significantly inhibited bacterial motility and expression of extracellular flagellin. We conclude that salicylidene acylhydrazides affect bacterial T3SS activity in S. enterica and hence could be used as lead substances when designing specific inhibitors of bacterial T3SSs in order to pharmaceutically intervene with bacterial virulence.
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Affiliation(s)
- Aurel Negrea
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Nobels väg 16, Stockholm, Sweden
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Bjur E, Eriksson-Ygberg S, Aslund F, Rhen M. Thioredoxin 1 promotes intracellular replication and virulence of Salmonella enterica serovar Typhimurium. Infect Immun 2006; 74:5140-51. [PMID: 16926406 PMCID: PMC1594827 DOI: 10.1128/iai.00449-06] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The effect of the cytoplasmic reductase and protein chaperone thioredoxin 1 on the virulence of Salmonella enterica serovar Typhimurium was evaluated by deleting the trxA, trxB, or trxC gene of the cellular thioredoxin system, the grxA or gshA gene of the glutathione/glutaredoxin system, or the dsbC gene coding for a thioredoxin-dependent periplasmic disulfide bond isomerase. Mutants were tested for tolerance to oxidative and nitric oxide donor substances in vitro, for invasion and intracellular replication in cultured epithelial and macrophage-like cells, and for virulence in BALB/c mice. In these experiments only the gshA mutant, which was defective in glutathione synthesis, exhibited sensitization to oxidative stress in vitro and a small decrease in virulence. In contrast, the trxA mutant did not exhibit any growth defects or decreased tolerance to oxidative or nitric oxide stress in vitro, yet there were pronounced decreases in intracellular replication and mouse virulence. Complementation analyses using defined catalytic variants of thioredoxin 1 showed that there is a direct correlation between the redox potential of thioredoxin 1 and restoration of intracellular replication of the trxA mutant. Attenuation of mouse virulence that was caused by a deficiency in thioredoxin 1 was restored by expression of wild-type thioredoxin 1 in trans but not by expression of a catalytically inactive variant. These results clearly imply that in S. enterica serovar Typhimurium, the redox-active protein thioredoxin 1 promotes virulence, whereas in vitro tolerance to oxidative stress depends on production of glutathione.
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Affiliation(s)
- Eva Bjur
- Microbiology and Tumor Biology Center, Karolinska Institutet, Nobels väg 16, 177 71 Stockholm, Sweden.
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