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Köppen K, Fatykhova D, Holland G, Rauch J, Tappe D, Graff M, Rydzewski K, Hocke AC, Hippenstiel S, Heuner K. Ex vivo infection model for Francisella using human lung tissue. Front Cell Infect Microbiol 2023; 13:1224356. [PMID: 37492528 PMCID: PMC10365108 DOI: 10.3389/fcimb.2023.1224356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 06/23/2023] [Indexed: 07/27/2023] Open
Abstract
Introduction Tularemia is mainly caused by Francisella tularensis (Ft) subsp. tularensis (Ftt) and Ft subsp. holarctica (Ftt) in humans and in more than 200 animal species including rabbits and hares. Human clinical manifestations depend on the route of infection and range from flu-like symptoms to severe pneumonia with a mortality rate up to 60% without treatment. So far, only 2D cell culture and animal models are used to study Francisella virulence, but the gained results are transferable to human infections only to a certain extent. Method In this study, we firstly established an ex vivo human lung tissue infection model using different Francisella strains: Ftt Life Vaccine Strain (LVS), Ftt LVS ΔiglC, Ftt human clinical isolate A-660 and a German environmental Francisella species strain W12-1067 (F-W12). Human lung tissue was used to determine the colony forming units and to detect infected cell types by using spectral immunofluorescence and electron microscopy. Chemokine and cytokine levels were measured in culture supernatants. Results Only LVS and A-660 were able to grow within the human lung explants, whereas LVS ΔiglC and F-W12 did not replicate. Using human lung tissue, we observed a greater increase of bacterial load per explant for patient isolate A-660 compared to LVS, whereas a similar replication of both strains was observed in cell culture models with human macrophages. Alveolar macrophages were mainly infected in human lung tissue, but Ftt was also sporadically detected within white blood cells. Although Ftt replicated within lung tissue, an overall low induction of pro-inflammatory cytokines and chemokines was observed. A-660-infected lung explants secreted slightly less of IL-1β, MCP-1, IP-10 and IL-6 compared to Ftt LVS-infected explants, suggesting a more repressed immune response for patient isolate A-660. When LVS and A-660 were used for simultaneous co-infections, only the ex vivo model reflected the less virulent phenotype of LVS, as it was outcompeted by A-660. Conclusion We successfully implemented an ex vivo infection model using human lung tissue for Francisella. The model delivers considerable advantages and is able to discriminate virulent Francisella from less- or non-virulent strains and can be used to investigate the role of specific virulence factors.
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Affiliation(s)
- Kristin Köppen
- Working group “Cellular Interactions of Bacterial Pathogens”, Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
| | - Diana Fatykhova
- Department of Infectious Diseases, Respiratory Medicine and Critical Care, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
| | - Gudrun Holland
- Advanced Light and Electron Microscopy, ZBS 4, Robert Koch Institute, Berlin, Germany
| | - Jessica Rauch
- Research Group Zoonoses, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
| | - Dennis Tappe
- Research Group Zoonoses, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
| | - Mareike Graff
- Department for General and Thoracic Surgery, DRK Clinics, Berlin, Germany
| | - Kerstin Rydzewski
- Working group “Cellular Interactions of Bacterial Pathogens”, Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
| | - Andreas C. Hocke
- Department of Infectious Diseases, Respiratory Medicine and Critical Care, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
| | - Stefan Hippenstiel
- Department of Infectious Diseases, Respiratory Medicine and Critical Care, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany
| | - Klaus Heuner
- Working group “Cellular Interactions of Bacterial Pathogens”, Centre for Biological Threats and Special Pathogens, Highly Pathogenic Microorganisms (ZBS 2), Robert Koch Institute, Berlin, Germany
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Rytter H, Jamet A, Ziveri J, Ramond E, Coureuil M, Lagouge-Roussey P, Euphrasie D, Tros F, Goudin N, Chhuon C, Nemazanyy I, de Moraes FE, Labate C, Guerrera IC, Charbit A. The pentose phosphate pathway constitutes a major metabolic hub in pathogenic Francisella. PLoS Pathog 2021; 17:e1009326. [PMID: 34339477 PMCID: PMC8360588 DOI: 10.1371/journal.ppat.1009326] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 08/12/2021] [Accepted: 07/14/2021] [Indexed: 11/19/2022] Open
Abstract
Metabolic pathways are now considered as intrinsic virulence attributes of pathogenic bacteria and thus represent potential targets for antibacterial strategies. Here we focused on the role of the pentose phosphate pathway (PPP) and its connections with other metabolic pathways in the pathophysiology of Francisella novicida. The involvement of the PPP in the intracellular life cycle of Francisella was first demonstrated by studying PPP inactivating mutants. Indeed, we observed that inactivation of the tktA, rpiA or rpe genes severely impaired intramacrophage multiplication during the first 24 hours. However, time-lapse video microscopy demonstrated that rpiA and rpe mutants were able to resume late intracellular multiplication. To better understand the links between PPP and other metabolic networks in the bacterium, we also performed an extensive proteo-metabolomic analysis of these mutants. We show that the PPP constitutes a major bacterial metabolic hub with multiple connections to glycolysis, the tricarboxylic acid cycle and other pathways, such as fatty acid degradation and sulfur metabolism. Altogether our study highlights how PPP plays a key role in the pathogenesis and growth of Francisella in its intracellular niche.
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Affiliation(s)
- Héloise Rytter
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Anne Jamet
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Jason Ziveri
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Elodie Ramond
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Mathieu Coureuil
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Pauline Lagouge-Roussey
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Daniel Euphrasie
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Fabiola Tros
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
| | - Nicolas Goudin
- Pole Bio-analyse d’images, Structure Fédérative de Recherche Necker INSERM US24- CNRS UMS 3633, Paris, France
| | - Cerina Chhuon
- Université de Paris, Paris, France
- Plateforme Protéome Institut Necker, PPN, Structure Fédérative de Recherche Necker INSERM US24-CNRS UMS 3633, Paris, France
| | - Ivan Nemazanyy
- Université de Paris, Paris, France
- Plateforme Etude du métabolisme, Structure Fédérative de Recherche Necker INSERM US24-CNRS UMS 3633, Paris, France
| | - Fabricio Edgar de Moraes
- Laboratório Max Feffer de Genética de Plantas, Departamento de Genética, Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo, Piracicaba, Brazil
| | - Carlos Labate
- Laboratório Max Feffer de Genética de Plantas, Departamento de Genética, Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo, Piracicaba, Brazil
| | - Ida Chiara Guerrera
- Université de Paris, Paris, France
- Plateforme Protéome Institut Necker, PPN, Structure Fédérative de Recherche Necker INSERM US24-CNRS UMS 3633, Paris, France
- * E-mail: (ICG); (AC)
| | - Alain Charbit
- Université de Paris, Paris, France
- INSERM U1151 - CNRS UMR 8253, Institut Necker-Enfants Malades. Team 7: Pathogénie des Infections Systémiques, Paris, France
- * E-mail: (ICG); (AC)
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Ramsey KM, Ledvina HE, Tresko TM, Wandzilak JM, Tower CA, Tallo T, Schramm CE, Peterson SB, Skerrett SJ, Mougous JD, Dove SL. Tn-Seq reveals hidden complexity in the utilization of host-derived glutathione in Francisella tularensis. PLoS Pathog 2020; 16:e1008566. [PMID: 32492066 PMCID: PMC7340319 DOI: 10.1371/journal.ppat.1008566] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 07/07/2020] [Accepted: 04/20/2020] [Indexed: 12/27/2022] Open
Abstract
Host-derived glutathione (GSH) is an essential source of cysteine for the intracellular pathogen Francisella tularensis. In a comprehensive transposon insertion sequencing screen, we identified several F. tularensis genes that play central and previously unappreciated roles in the utilization of GSH during the growth of the bacterium in macrophages. We show that one of these, a gene we named dptA, encodes a proton-dependent oligopeptide transporter that enables growth of the organism on the dipeptide Cys-Gly, a key breakdown product of GSH generated by the enzyme γ-glutamyltranspeptidase (GGT). Although GGT was thought to be the principal enzyme involved in GSH breakdown in F. tularensis, our screen identified a second enzyme, referred to as ChaC, that is also involved in the utilization of exogenous GSH. However, unlike GGT and DptA, we show that the importance of ChaC in supporting intramacrophage growth extends beyond cysteine acquisition. Taken together, our findings provide a compendium of F. tularensis genes required for intracellular growth and identify new players in the metabolism of GSH that could be attractive targets for therapeutic intervention.
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Affiliation(s)
- Kathryn M. Ramsey
- Division of Infectious Diseases, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
- Departments of Cell and Molecular Biology and Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, Rhode Island, United States of America
| | - Hannah E. Ledvina
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Tenayaann M. Tresko
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Jamie M. Wandzilak
- Departments of Cell and Molecular Biology and Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, Rhode Island, United States of America
| | - Catherine A. Tower
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Thomas Tallo
- Division of Infectious Diseases, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Caroline E. Schramm
- Division of Pulmonary, Critical Care and Sleep Medicine, Harborview Medical Center, University of Washington, Seattle, Washington, United States of America
| | - S. Brook Peterson
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Shawn J. Skerrett
- Division of Pulmonary, Critical Care and Sleep Medicine, Harborview Medical Center, University of Washington, Seattle, Washington, United States of America
| | - Joseph D. Mougous
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
- Howard Hughes Medical Institute, University of Washington, Seattle, Washington, United States of America
| | - Simon L. Dove
- Division of Infectious Diseases, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
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Screen for fitness and virulence factors of Francisella sp. strain W12-1067 using amoebae. Int J Med Microbiol 2019; 309:151341. [PMID: 31451389 DOI: 10.1016/j.ijmm.2019.151341] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 07/17/2019] [Accepted: 08/18/2019] [Indexed: 11/21/2022] Open
Abstract
Francisella tularensis is the causative agent of the human disease referred to as tularemia. Other Francisella species are known but less is understood about their virulence factors. The role of environmental amoebae in the life-cycle of Francisella is still under discussion. Francisella sp. strain W12-1067 (F-W12) is an environmental Francisella isolate recently identified in Germany which is negative for the Francisella pathogenicity island, but exhibits a putative alternative type VI secretion system. Putative virulence factors have been identified in silico in the genome of F-W12. In this work, we established a "scatter screen", used earlier for pathogenic Legionella, to verify experimentally and identify candidate fitness factors using a transposon mutant bank of F-W12 and Acanthamoeba lenticulata as host organism. In these experiments, we identified 79 scatter clones (amoeba sensitive), which were further analyzed by an infection assay identifying 9 known virulence factors, but also candidate fitness factors of F-W12 not yet described as fitness factors in Francisella. The majority of the identified genes encoded proteins involved in the synthesis or maintenance of the cell envelope (LPS, outer membrane, capsule) or in the metabolism (glycolysis, gluconeogenesis, pentose phosphate pathway). Further 13C-flux analysis of the Tn5 glucokinase mutant strain revealed that the identified gene indeed encodes the sole active glucokinase in F-W12. In conclusion, candidate fitness factors of the new Francisella species F-W12 were identified using the scatter screen method which might also be usable for other Francisella species.
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Cui G, Wang J, Qi X, Su J. Transcription Elongation Factor GreA Plays a Key Role in Cellular Invasion and Virulence of Francisella tularensis subsp. novicida. Sci Rep 2018; 8:6895. [PMID: 29720697 PMCID: PMC5932009 DOI: 10.1038/s41598-018-25271-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Accepted: 04/18/2018] [Indexed: 01/24/2023] Open
Abstract
Francisella tularensis is a facultative intracellular Gram-negative bacterium that causes the zoonotic disease tularemia. We identified the transcription elongation factor GreA as a virulence factor in our previous study, but its role was not defined. Here, we investigate the effects of the inactivation of the greA gene, generating a greA mutant of F. tularensis subsp. novicida. Inactivation of greA impaired the bacterial invasion into and growth within host cells, and subsequently virulence in mouse infection model. A transcriptomic analysis (RNA-Seq) showed that the loss of GreA caused the differential expression of 196 bacterial genes, 77 of which were identified as virulence factors in previous studies. To confirm that GreA regulates the expression of virulence factors involved in cell invasion by Francisella, FTN_1186 (pepO) and FTN_1551 (ampD) gene mutants were generated. The ampD deletion mutant showed reduced invasiveness into host cells. These results strongly suggest that GreA plays an important role in the pathogenesis of Francisella by affecting the expression of virulence genes and provide new insights into the complex regulation of Francisella infection.
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Affiliation(s)
- Guolin Cui
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, 100193, China
| | - Jun Wang
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, 100193, China
| | - Xinyi Qi
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, 100193, China
| | - Jingliang Su
- Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, 100193, China.
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Spidlova P, Stojkova P, Dankova V, Senitkova I, Santic M, Pinkas D, Philimonenko V, Stulik J. Francisella tularensis D-Ala D-Ala Carboxypeptidase DacD Is Involved in Intracellular Replication and It Is Necessary for Bacterial Cell Wall Integrity. Front Cell Infect Microbiol 2018; 8:111. [PMID: 29692981 PMCID: PMC5903032 DOI: 10.3389/fcimb.2018.00111] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 03/21/2018] [Indexed: 12/16/2022] Open
Abstract
D-alanyl-D-alanine carboxypeptidase, product of dacD gene in Francisella, belongs to penicillin binding proteins (PBPs) and is involved in remodeling of newly synthetized peptidoglycan. In E. coli, PBPs are synthetized in various growth phases and they are able to substitute each other to a certain extent. The DacD protein was found to be accumulated in fraction enriched in membrane proteins from severely attenuated dsbA deletion mutant strain. It has been presumed that the DsbA is not a virulence factor by itself but that its substrates, whose correct folding and topology are dependent on the DsbA oxidoreductase and/or isomerase activities, are the primary virulence factors. Here we demonstrate that Francisella DacD is required for intracellular replication and virulence in mice. The dacD insertion mutant strain showed higher sensitivity to acidic pH, high temperature and high osmolarity when compared to the wild-type. Eventually, transmission electron microscopy revealed differences in mutant bacteria in both the size and defects in outer membrane underlying its SDS and serum sensitivity. Taken together these results suggest DacD plays an important role in Francisella pathogenicity.
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Affiliation(s)
- Petra Spidlova
- Department of Molecular Pathology and Biology, Faculty of Military Health Sciences, University of Defence, Hradec Kralove, Czechia
| | - Pavla Stojkova
- Department of Molecular Pathology and Biology, Faculty of Military Health Sciences, University of Defence, Hradec Kralove, Czechia
| | - Vera Dankova
- Department of Molecular Pathology and Biology, Faculty of Military Health Sciences, University of Defence, Hradec Kralove, Czechia
| | - Iva Senitkova
- Department of Molecular Pathology and Biology, Faculty of Military Health Sciences, University of Defence, Hradec Kralove, Czechia
| | - Marina Santic
- Department of Microbiology and Parasitology, Medical Faculty, University of Rijeka, Rijeka, Croatia
| | - Dominik Pinkas
- Microscopy Center, Institute of Molecular Genetics ASCR v.v.i., Electron Microscopy Core Facility, Prague, Czechia
| | - Vlada Philimonenko
- Microscopy Center, Institute of Molecular Genetics ASCR v.v.i., Electron Microscopy Core Facility, Prague, Czechia
- Department of Biology of the Cell Nucleus, Institute of Molecular Genetics ASCR v.v.i., Prague, Czechia
| | - Jiri Stulik
- Department of Molecular Pathology and Biology, Faculty of Military Health Sciences, University of Defence, Hradec Kralove, Czechia
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7
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Kenney A, Cusick A, Payne J, Gaughenbaugh A, Renshaw A, Wright J, Seeber R, Barnes R, Florjanczyk A, Horzempa J. The potential for flower nectar to allow mosquito to mosquito transmission of Francisella tularensis. PLoS One 2017; 12:e0175157. [PMID: 28486521 PMCID: PMC5423603 DOI: 10.1371/journal.pone.0175157] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 03/21/2017] [Indexed: 11/22/2022] Open
Abstract
Francisella tularensis is disseminated in nature by biting arthropods such as mosquitoes. The relationship between mosquitoes and F. tularensis in nature is highly ambiguous, due in part to the fact that mosquitoes have caused significant tularemia outbreaks despite being classified as a mechanical vector of F. tularensis. One possible explanation for mosquitoes being a prominent, yet mechanical vector is that these insects feed on flower nectar between blood meals, allowing for transmission of F. tularensis between mosquitoes. Here, we aimed to assess whether F. tularensis could survive in flower nectar. Moreover, we examined if mosquitoes could interact with or ingest and transmit F. tularensis from one source of nectar to another. F. tularensis exhibited robust survivability in flower nectar with concentrations of viable bacteria remaining consistent with the rich growth medium. Furthermore, F. tularensis was able to survive (albeit to a lesser extent) in 30% sucrose (a nectar surrogate) over a period of time consistent with that of a typical flower bloom. Although we observed diminished bacterial survival in the nectar surrogate, mosquitoes that fed on this material became colonized with F. tularensis. Finally, colonized mosquitoes were capable of transferring F. tularensis to a sterile nectar surrogate. These data suggest that flower nectar may be capable of serving as a temporary source of F. tularensis that could contribute to the amplification of outbreaks. Mosquitoes that feed on an infected mammalian host and subsequently feed on flower nectar could deposit some F. tularensis bacteria into the nectar in the process. Mosquitoes subsequently feeding on this nectar source could potentially become colonized by F. tularensis. Thus, the possibility exists that flower nectar may allow for vector-vector transmission of F. tularensis.
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Affiliation(s)
- Adam Kenney
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Austin Cusick
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Jessica Payne
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Anna Gaughenbaugh
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Andrea Renshaw
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Jenna Wright
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Roger Seeber
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Rebecca Barnes
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Aleksandr Florjanczyk
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
| | - Joseph Horzempa
- Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, West Virginia, United States of America
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Ramakrishnan G. Iron and Virulence in Francisella tularensis. Front Cell Infect Microbiol 2017; 7:107. [PMID: 28421167 PMCID: PMC5378763 DOI: 10.3389/fcimb.2017.00107] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 03/16/2017] [Indexed: 12/12/2022] Open
Abstract
Francisella tularensis, the causative agent of tularemia, is a Gram-negative bacterium that infects a variety of cell types including macrophages, and propagates with great efficiency in the cytoplasm. Iron, essential for key enzymatic and redox reactions, is among the nutrients required to support this pathogenic lifestyle and the bacterium relies on specialized mechanisms to acquire iron within the host environment. Two distinct pathways for iron acquisition are encoded by the F. tularensis genome- a siderophore-dependent ferric iron uptake system and a ferrous iron transport system. Genes of the Fur-regulated fslABCDEF operon direct the production and transport of the siderophore rhizoferrin. Siderophore biosynthesis involves enzymes FslA and FslC, while export across the inner membrane is mediated by FslB. Uptake of the rhizoferrin- ferric iron complex is effected by the siderophore receptor FslE in the outer membrane in a TonB-independent process, and FslD is responsible for uptake across the inner membrane. Ferrous iron uptake relies largely on high affinity transport by FupA in the outer membrane, while the Fur-regulated FeoB protein mediates transport across the inner membrane. FslE and FupA are paralogous proteins, sharing sequence similarity and possibly sharing structural features as well. This review summarizes current knowledge of iron acquisition in this organism and the critical role of these uptake systems in bacterial pathogenicity.
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Affiliation(s)
- Girija Ramakrishnan
- Department of Medicine/Division of Infectious Diseases, University of VirginiaCharlottesville, VA, USA
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Qin A, Zhang Y, Clark ME, Moore EA, Rabideau MM, Moreau GB, Mann BJ. Components of the type six secretion system are substrates of Francisella tularensis Schu S4 DsbA-like FipB protein. Virulence 2016; 7:882-894. [PMID: 27028889 PMCID: PMC5160417 DOI: 10.1080/21505594.2016.1168550] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
FipB, an essential virulence factor in the highly virulent Schu S4 strain of F. tularensis subsp. tularensis, shares sequence similarity with Disulfide Bond formation (Dsb) proteins, which can have oxidoreductase, isomerase, or chaperone activity. To further explore FipB's role in virulence potential substrates were identified by co-purification and 2D gel electrophoresis, followed by protein sequencing using mass spectrometry. A total of 119 potential substrates were identified. Proteins with predicted enzymatic activity were prevalent, and there were 19 proteins that had been previously identified as impacting virulence. Among the potential substrates were IglC, IglB, and PdpB, three components of the Francisella Type Six Secretion System (T6SS), which is also essential for virulence. T6SS are widespread in Gram-negative pathogens, but have not been reported to be dependent on Dsb-like proteins for assembly or function. The presented results suggest that FipB affects IglB and IglC substrates differently. In a fipB mutant there were differences in free sulfhydryl accessibility of IglC, but not IglB, when compared to wild-type bacteria. However, for both proteins FipB appears to act as a chaperone that facilitates proper folding and conformation. Understanding the role FipB plays the assembly and structure in this T6SS may reveal critical aspects of assembly that are common and novel among this widely distributed class of secretion systems.
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Affiliation(s)
- Aiping Qin
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - Yan Zhang
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - Melinda E Clark
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - Emily A Moore
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - Meaghan M Rabideau
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - G Brett Moreau
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
| | - Barbara J Mann
- a Department of Medicine , Division of Infectious Diseases, University of Virginia , Charlottesville , VA , USA
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The Divergent Intracellular Lifestyle of Francisella tularensis in Evolutionarily Distinct Host Cells. PLoS Pathog 2015; 11:e1005208. [PMID: 26633893 PMCID: PMC4669081 DOI: 10.1371/journal.ppat.1005208] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
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11
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Identification of novel members of the bacterial azoreductase family in Pseudomonas aeruginosa. Biochem J 2015; 473:549-58. [PMID: 26621870 DOI: 10.1042/bj20150856] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 11/30/2015] [Indexed: 11/17/2022]
Abstract
Azoreductases are a family of diverse enzymes found in many pathogenic bacteria as well as distant homologues being present in eukarya. In addition to having azoreductase activity, these enzymes are also suggested to have NAD(P)H quinone oxidoreductase (NQO) activity which leads to a proposed role in plant pathogenesis. Azoreductases have also been suggested to play a role in the mammalian pathogenesis of Pseudomonas aeruginosa. In view of the importance of P. aeruginosa as a pathogen, we therefore characterized recombinant enzymes following expression of a group of putative azoreductase genes from P. aeruginosa expressed in Escherichia coli. The enzymes include members of the arsenic-resistance protein H (ArsH), tryptophan repressor-binding protein A (WrbA), modulator of drug activity B (MdaB) and YieF families. The ArsH, MdaB and YieF family members all show azoreductase and NQO activities. In contrast, WrbA is the first enzyme to show NQO activity but does not reduce any of the 11 azo compounds tested under a wide range of conditions. These studies will allow further investigation of the possible role of these enzymes in the pathogenesis of P. aeruginosa.
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Earl SC, Rogers MT, Keen J, Bland DM, Houppert AS, Miller C, Temple I, Anderson DM, Marketon MM. Resistance to Innate Immunity Contributes to Colonization of the Insect Gut by Yersinia pestis. PLoS One 2015; 10:e0133318. [PMID: 26177454 PMCID: PMC4503695 DOI: 10.1371/journal.pone.0133318] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 06/25/2015] [Indexed: 01/29/2023] Open
Abstract
Yersinia pestis, the causative agent of bubonic and pneumonic plague, is typically a zoonotic vector-borne disease of wild rodents. Bacterial biofilm formation in the proventriculus of the flea contributes to chronic infection of fleas and facilitates efficient disease transmission. However prior to biofilm formation, ingested bacteria must survive within the flea midgut, and yet little is known about vector-pathogen interactions that are required for flea gut colonization. Here we establish a Drosophila melanogaster model system to gain insight into Y. pestis colonization of the insect vector. We show that Y. pestis establishes a stable infection in the anterior midgut of fly larvae, and we used this model system to study the roles of genes involved in biofilm production and/or resistance to gut immunity stressors. We find that PhoP and GmhA both contribute to colonization and resistance to antimicrobial peptides in flies, and furthermore, the data suggest biofilm formation may afford protection against antimicrobial peptides. Production of reactive oxygen species in the fly gut, as in fleas, also serves to limit bacterial infection, and OxyR mediates Y. pestis survival in both insect models. Overall, our data establish the fruit fly as an informative model to elucidate the relationship between Y. pestis and its flea vector.
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Affiliation(s)
- Shaun C. Earl
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Miles T. Rogers
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Jennifer Keen
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - David M. Bland
- Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri, United States of America
| | - Andrew S. Houppert
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Caitlynn Miller
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Ian Temple
- Department of Biology, Indiana University, Bloomington, IN, United States of America
| | - Deborah M. Anderson
- Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri, United States of America
| | - Melanie M. Marketon
- Department of Biology, Indiana University, Bloomington, IN, United States of America
- * E-mail:
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Barel M, Ramond E, Gesbert G, Charbit A. The complex amino acid diet of Francisella in infected macrophages. Front Cell Infect Microbiol 2015; 5:9. [PMID: 25705612 PMCID: PMC4319460 DOI: 10.3389/fcimb.2015.00009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 01/14/2015] [Indexed: 12/16/2022] Open
Abstract
Francisella tularensis, the agent of the zoonotic disease tularemia, is a highly infectious bacterium for a large number of animal species and can be transmitted to humans by various means. The bacterium is able to infect a variety of cell types but replicates in mammalian hosts mainly in the cytosol of infected macrophages. In order to resist the stressful and nutrient-restricted intracellular environments, it encounters during its systemic dissemination, Francisella has developed dedicated stress resistance mechanisms and adapted its metabolic and nutritional needs. Recent data form our laboratory and from several other groups have shown that Francisella simultaneously relies on multiple host amino acid sources during its intracellular life cycle. This review will summarize how intracellular Francisella use different amino acid sources, and their role in phagosomal escape and/or cytosolic multiplication and systemic dissemination. We will first summarize the data that we have obtained on two amino acid transporters involved in Francisella phagosomal escape and cytosolic multiplication i.e., the glutamate transporter GadC and the asparagine transporter AnsP, respectively. The specific contribution of glutamate and asparagine to the physiology of the bacterium will be evoked. Then, we will discuss how Francisella has adapted to obtain and utilize host amino acid resources, and notably the contribution of host transporters and autophagy process in the establishment of a nutrient-replete intracellular niche.
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Affiliation(s)
- Monique Barel
- Université Paris Descartes, Sorbonne Paris Cité Paris, France ; INSERM U1151 - Centre National de la Recherche Scientifique UMR 8253, Institut Necker-Enfants Malades Paris, France
| | - Elodie Ramond
- Université Paris Descartes, Sorbonne Paris Cité Paris, France ; INSERM U1151 - Centre National de la Recherche Scientifique UMR 8253, Institut Necker-Enfants Malades Paris, France
| | - Gael Gesbert
- Université Paris Descartes, Sorbonne Paris Cité Paris, France ; INSERM U1151 - Centre National de la Recherche Scientifique UMR 8253, Institut Necker-Enfants Malades Paris, France
| | - Alain Charbit
- Université Paris Descartes, Sorbonne Paris Cité Paris, France ; INSERM U1151 - Centre National de la Recherche Scientifique UMR 8253, Institut Necker-Enfants Malades Paris, France
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14
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Genome sequence and phenotypic analysis of a first German Francisella sp. isolate (W12-1067) not belonging to the species Francisella tularensis. BMC Microbiol 2014; 14:169. [PMID: 24961323 PMCID: PMC4230796 DOI: 10.1186/1471-2180-14-169] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 06/19/2014] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND Francisella isolates from patients suffering from tularemia in Germany are generally strains of the species F. tularensis subsp. holarctica. To our knowledge, no other Francisella species are known for Germany. Recently, a new Francisella species could be isolated from a water reservoir of a cooling tower in Germany. RESULTS We identified a Francisella sp. (isolate W12-1067) whose 16S rDNA is 99% identical to the respective nucleotide sequence of the recently published strain F. guangzhouensis. The overall sequence identity of the fopA, gyrA, rpoA, groEL, sdhA and dnaK genes is only 89%, indicating that strain W12-1067 is not identical to F. guangzhouensis. W12-1067 was isolated from a water reservoir of a cooling tower of a hospital in Germany. The growth optimum of the isolate is approximately 30°C, it can grow in the presence of 4-5% NaCl (halotolerant) and is able to grow without additional cysteine within the medium. The strain was able to replicate within a mouse-derived macrophage-like cell line. The whole genome of the strain was sequenced (~1.7 mbp, 32.2% G + C content) and the draft genome was annotated. Various virulence genes common to the genus Francisella are present, but the Francisella pathogenicity island (FPI) is missing. However, another putative type-VI secretion system is present within the genome of strain W12-1067. CONCLUSIONS Isolate W12-1067 is closely related to the recently described F. guangzhouensis species and it replicates within eukaryotic host cells. Since W12-1067 exhibits a putative new type-VI secretion system and F. tularensis subsp. holarctica was found not to be the sole species in Germany, the new isolate is an interesting species to be analyzed in more detail. Further research is needed to investigate the epidemiology, ecology and pathogenicity of Francisella species present in Germany.
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Panayidou S, Ioannidou E, Apidianakis Y. Human pathogenic bacteria, fungi, and viruses in Drosophila: disease modeling, lessons, and shortcomings. Virulence 2014; 5:253-69. [PMID: 24398387 DOI: 10.4161/viru.27524] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Drosophila has been the invertebrate model organism of choice for the study of innate immune responses during the past few decades. Many Drosophila-microbe interaction studies have helped to define innate immunity pathways, and significant effort has been made lately to decipher mechanisms of microbial pathogenesis. Here we catalog 68 bacterial, fungal, and viral species studied in flies, 43 of which are relevant to human health. We discuss studies of human pathogens in flies revealing not only the elicitation and avoidance of immune response but also mechanisms of tolerance, host tissue homeostasis, regeneration, and predisposition to cancer. Prominent among those is the emerging pattern of intestinal regeneration as a defense response induced by pathogenic and innocuous bacteria. Immunopathology mechanisms and many microbial virulence factors have been elucidated, but their relevance to human health conventionally necessitates validation in mammalian models of infection.
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Affiliation(s)
- Stavria Panayidou
- Department of Biological Sciences; University of Cyprus; Nicosia, Cyprus
| | - Eleni Ioannidou
- Department of Biological Sciences; University of Cyprus; Nicosia, Cyprus
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Ramond E, Gesbert G, Rigard M, Dairou J, Dupuis M, Dubail I, Meibom K, Henry T, Barel M, Charbit A. Glutamate utilization couples oxidative stress defense and the tricarboxylic acid cycle in Francisella phagosomal escape. PLoS Pathog 2014; 10:e1003893. [PMID: 24453979 PMCID: PMC3894225 DOI: 10.1371/journal.ppat.1003893] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 12/05/2013] [Indexed: 11/18/2022] Open
Abstract
Intracellular bacterial pathogens have developed a variety of strategies to avoid degradation by the host innate immune defense mechanisms triggered upon phagocytocis. Upon infection of mammalian host cells, the intracellular pathogen Francisella replicates exclusively in the cytosolic compartment. Hence, its ability to escape rapidly from the phagosomal compartment is critical for its pathogenicity. Here, we show for the first time that a glutamate transporter of Francisella (here designated GadC) is critical for oxidative stress defense in the phagosome, thus impairing intra-macrophage multiplication and virulence in the mouse model. The gadC mutant failed to efficiently neutralize the production of reactive oxygen species. Remarkably, virulence of the gadC mutant was partially restored in mice defective in NADPH oxidase activity. The data presented highlight links between glutamate uptake, oxidative stress defense, the tricarboxylic acid cycle and phagosomal escape. This is the first report establishing the role of an amino acid transporter in the early stage of the Francisella intracellular lifecycle.
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Affiliation(s)
- Elodie Ramond
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Gael Gesbert
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Mélanie Rigard
- Centre international de recherche en infectiologie, Université de Lyon, Lyon, France
- Bacterial Pathogenesis and Innate Immunity Laboratory, INSERM U851 “Immunity, Infection and Vaccination”, Lyon, France
| | - Julien Dairou
- Platform “Bioprofiler” Université Paris Diderot, Paris, France
| | - Marion Dupuis
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Iharilalao Dubail
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Karin Meibom
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Thomas Henry
- Centre international de recherche en infectiologie, Université de Lyon, Lyon, France
- Bacterial Pathogenesis and Innate Immunity Laboratory, INSERM U851 “Immunity, Infection and Vaccination”, Lyon, France
| | - Monique Barel
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
| | - Alain Charbit
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, Paris, France
- INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
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17
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Abstract
Our understanding of the virulence and pathogenesis of Francisella spp. has significantly advanced in recent years, including a new understanding that this organism can form biofilms. What is known so far about Francisella spp. biofilms is summarized here and future research questions are suggested. The molecular basis of biofilm production has begun to be studied, especially the role of extracellular carbohydrates and capsule, quorum sensing and two-component signaling systems. Further work has explored the contribution of amoebae, pili, outer-membrane vesicles, chitinases, and small molecules such as c-di-GMP to Francisella spp. biofilm formation. A role for Francisella spp. biofilm in feeding mosquito larvae has been suggested. As no strong role in virulence has been found yet, Francisella spp. biofilm formation is most likely a key mechanism for environmental survival and persistence. The significance and importance of Francisella spp.’s biofilm phenotype as a critical aspect of its microbial physiology is being developed. Areas for further studies include the potential role of Francisella spp. biofilms in the infection of mammalian hosts and virulence regulation.
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Affiliation(s)
- Monique L van Hoek
- School of Systems Biology and National Center for Biodefense and Infectious Diseases; George Mason University; Manassas, VA USA
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18
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Gesbert G, Ramond E, Rigard M, Frapy E, Dupuis M, Dubail I, Barel M, Henry T, Meibom K, Charbit A. Asparagine assimilation is critical for intracellular replication and dissemination of Francisella. Cell Microbiol 2013; 16:434-49. [PMID: 24134488 DOI: 10.1111/cmi.12227] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 10/10/2013] [Accepted: 10/11/2013] [Indexed: 12/28/2022]
Abstract
In order to develop a successful infectious cycle, intracellular bacterial pathogens must be able to adapt their metabolism to optimally utilize the nutrients available in the cellular compartments and tissues where they reside. Francisella tularensis, the agent of the zoonotic disease tularaemia, is a highly infectious bacterium for a large number of animal species. This bacterium replicates in its mammalian hosts mainly in the cytosol of infected macrophages. We report here the identification of a novel amino acid transporter of the major facilitator superfamily of secondary transporters that is required for bacterial intracellular multiplication and systemic dissemination. We show that inactivation of this transporter does not affect phagosomal escape but prevents multiplication in the cytosol of all cell types tested. Remarkably, the intracellular growth defect of the mutant was fully and specifically reversed by addition of asparagine or asparagine-containing dipeptides as well as by simultaneous addition of aspartic acid and ammonium. Importantly, bacterial virulence was also restored in vivo, in the mouse model, by asparagine supplementation. This work unravels thus, for the first time, the importance of asparagine for cytosolicmultiplication of Francisella. Amino acid transporters are likely to constitute underappreciated players in bacterial intracellular parasitism.
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Affiliation(s)
- Gael Gesbert
- Université Paris Descartes, Sorbonne Paris Cité, Bâtiment Leriche, 96 rue Didot 75993, Paris, Cedex 14, France; INSERM, U1002, Unité de Pathogénie des Infections Systémiques, Paris, France
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19
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IglE is an outer membrane-associated lipoprotein essential for intracellular survival and murine virulence of type A Francisella tularensis. Infect Immun 2013; 81:4026-40. [PMID: 23959721 DOI: 10.1128/iai.00595-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
IglE is a small, hypothetical protein encoded by the duplicated Francisella pathogenicity island (FPI). Inactivation of both copies of iglE rendered Francisella tularensis subsp. tularensis Schu S4 avirulent and incapable of intracellular replication, owing to an inability to escape the phagosome. This defect was fully reversed following single-copy expression of iglE in trans from attTn7 under the control of the Francisella rpsL promoter, thereby establishing that the loss of iglE, and not polar effects on downstream vgrG gene expression, was responsible for the defect. IglE is exported to the Francisella outer membrane as an ∼13.9-kDa lipoprotein, determined on the basis of a combination of selective Triton X-114 solubilization, radiolabeling with [(3)H]palmitic acid, and sucrose density gradient membrane partitioning studies. Lastly, a genetic screen using the iglE-null live vaccine strain resulted in the identification of key regions in the carboxyl terminus of IglE that are required for intracellular replication of Francisella tularensis in J774A.1 macrophages. Thus, IglE is essential for Francisella tularensis virulence. Our data support a model that likely includes protein-protein interactions at or near the bacterial cell surface that are unknown at present.
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Woolard MD, Barrigan LM, Fuller JR, Buntzman AS, Bryan J, Manoil C, Kawula TH, Frelinger JA. Identification of Francisella novicida mutants that fail to induce prostaglandin E(2) synthesis by infected macrophages. Front Microbiol 2013; 4:16. [PMID: 23403609 PMCID: PMC3568750 DOI: 10.3389/fmicb.2013.00016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Accepted: 01/24/2013] [Indexed: 11/13/2022] Open
Abstract
Francisella tularensis is the causative agent of tularemia. We have previously shown that infection with F. tularensis Live Vaccine Strain (LVS) induces macrophages to synthesize prostaglandin E2 (PGE2). Synthesis of PGE2 by F. tularensis infected macrophages results in decreased T cell proliferation in vitro and increased bacterial survival in vivo. Although we understand some of the biological consequences of F. tularensis induced PGE2 synthesis by macrophages, we do not understand the cellular pathways (neither host nor bacterial) that result in up-regulation of the PGE2 biosynthetic pathway in F. tularensis infected macrophages. We took a genetic approach to begin to understand the molecular mechanisms of bacterial induction of PGE2 synthesis from infected macrophages. To identify F. tularensis genes necessary for the induction of PGE2 in primary macrophages, we infected cells with individual mutants from the closely related strain F. tularensis subspecies novicida U112 (U112) two allele mutant library. Twenty genes were identified that when disrupted resulted in U112 mutant strains unable to induce the synthesis of PGE2 by infected macrophages. Fourteen of the genes identified are located within the Francisella pathogenicity island (FPI). Genes in the FPI are required for F. tularensis to escape from the phagosome and replicate in the cytosol, which might account for the failure of U112 with transposon insertions within the FPI to induce PGE2. This implies that U112 mutant strains that do not grow intracellularly would also not induce PGE2. We found that U112 clpB::Tn grows within macrophages yet fails to induce PGE2, while U112 pdpA::Tn does not grow yet does induce PGE2. We also found that U112 iglC::Tn neither grows nor induces PGE2. These findings indicate that there is dissociation between intracellular growth and the ability of F. tularensis to induce PGE2 synthesis. These mutants provide a critical entrée into the pathways used in the host for PGE2 induction.
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Affiliation(s)
- Matthew D Woolard
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center at Shreveport Shreveport, LA, USA
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21
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Link between intraphagosomal biotin and rapid phagosomal escape in Francisella. Proc Natl Acad Sci U S A 2012; 109:18084-9. [PMID: 23071317 DOI: 10.1073/pnas.1206411109] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Cytosolic bacterial pathogens require extensive metabolic adaptations within the host to replicate intracellularly and cause disease. In phagocytic cells such as macrophages, these pathogens must respond rapidly to nutrient limitation within the harsh environment of the phagosome. Many cytosolic pathogens escape the phagosome quickly (15-60 min) and thereby subvert this host defense, reaching the cytosol where they can replicate. Although a great deal of research has focused on strategies used by bacteria to resist antimicrobial phagosomal defenses and transiently pass through this compartment, the metabolic requirements of bacteria in the phagosome are largely uncharacterized. We previously identified a Francisella protein, FTN_0818, as being essential for intracellular replication and involved in virulence in vivo. We now show that FTN_0818 is involved in biotin biosynthesis and required for rapid escape from the Francisella-containing phagosome (FCP). Addition of biotin complemented the phagosomal escape defect of the FTN_0818 mutant, demonstrating that biotin is critical for promoting rapid escape during the short time that the bacteria are in the phagosome. Biotin also rescued the attenuation of the FTN_0818 mutant during infection in vitro and in vivo, highlighting the importance of this process. The key role of biotin in phagosomal escape implies biotin may be a limiting factor during infection. We demonstrate that a bacterial metabolite is required for phagosomal escape of an intracellular pathogen, providing insight into the link between bacterial metabolism and virulence, likely serving as a paradigm for other cytosolic pathogens.
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Brennan LJ, Haukedal JA, Earle JC, Keddie B, Harris HL. Disruption of redox homeostasis leads to oxidative DNA damage in spermatocytes of Wolbachia-infected Drosophila simulans. INSECT MOLECULAR BIOLOGY 2012; 21:510-520. [PMID: 22831171 DOI: 10.1111/j.1365-2583.2012.01155.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Molecular interactions between symbiotic bacteria and their animal hosts are, as yet, poorly understood. The most widespread bacterial endosymbiont, Wolbachia pipientis, occurs in high density in testes of infected Drosophila simulans and causes cytoplasmic incompatibility (CI), a form of male-derived zygotic lethality. Wolbachia grow and divide within host vacuoles that generate reactive oxygen species (ROS), which in turn stimulate the up-regulation of antioxidant enzymes. These enzymes appear to protect the host from ROS-mediated damage, as there is no obvious fitness cost to Drosophila carrying Wolbachia infections. We have now determined that DNA from Wolbachia-infected mosquito Aedes albopictus (Aa23) cells shows a higher amount of the base 8-oxo-deoxyguanosine, a marker of oxidative DNA damage, than DNA from uninfected cells, and that Wolbachia infection in D. simulans is associated with an increase in DNA strand breaks in meiotic spermatocytes. Feeding exogenous antioxidants to male and female D. simulans dramatically increased Wolbachia numbers with no obvious effects on host fitness. These results suggest that ROS-induced DNA damage in sperm nuclei may contribute to the modification characteristic of CI expression in Wolbachia-infected males and that Wolbachia density is sensitive to redox balance in these flies.
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Affiliation(s)
- L J Brennan
- Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
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23
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Vonkavaara M, Pavel STI, Hölzl K, Nordfelth R, Sjöstedt A, Stöven S. Francisella is sensitive to insect antimicrobial peptides. J Innate Immun 2012; 5:50-9. [PMID: 23037919 DOI: 10.1159/000342468] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 08/01/2012] [Indexed: 12/24/2022] Open
Abstract
Francisella tularensis causes the zoonotic disease tularemia. Arthropod vectors are important transmission routes for the disease, although it is not known how Francisella survives the efficient arthropod immune response. Here, we used Drosophila melanogaster as a model host for Francisella infections and investigated whether the bacteria are resistant to insect humoral immune responses, in particular to the antimicrobial peptides (AMPs) secreted into the insect hemolymph. Moreover, we asked to what extent such resistance might depend on lipopolysaccharide (LPS) structure and surface characteristics of the bacteria. We analyzed Francisella novicida mutant strains in genes, directly or indirectly involved in specific steps of LPS biosynthesis, for virulence in wild-type and Relish(E20) immune-deficient flies, and tested selected mutants for sensitivity to AMPs in vitro. We demonstrate that Francisella is sensitive to specific fly AMPs, i.e. Attacin, Cecropin, Drosocin and Drosomycin. Furthermore, six bacterial genes, kpsF, manB, lpxF, slt, tolA and pal, were found to be required for resistance to Relish-dependent immune responses, illustrating the importance of structural details of Francisella lipid A and Kdo core for interactions with AMPs. Interestingly, a more negative surface charge and lack of O-antigen did not render mutant bacteria more sensitive to cationic AMPs and did not attenuate virulence in flies.
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Affiliation(s)
- Malin Vonkavaara
- Department of Clinical Microbiology, Umeå University, Umeå, Sweden
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24
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Identification of a novel small RNA modulating Francisella tularensis pathogenicity. PLoS One 2012; 7:e41999. [PMID: 22848684 PMCID: PMC3405028 DOI: 10.1371/journal.pone.0041999] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 06/28/2012] [Indexed: 01/21/2023] Open
Abstract
Francisella tularensis is a highly virulent bacterium responsible for the zoonotic disease tularemia. It is a facultative intracellular pathogen that replicates in the cytoplasm of host cells, particularly in macrophages. Here we show that F. tularensis live vaccine strain (LVS) expresses a novel small RNA (sRNA), which modulates the virulence capacities of the bacterium. When this sRNA, designated FtrC (for Francisella tularensisRNA C), is expressed at high levels, F. tularensis replicates in macrophages less efficiently than the wild-type parent strain. Similarly, high expression of FtrC reduces the number of viable bacteria recovered from the spleen and liver of infected mice. Our data demonstrate that expression of gene FTL_1293 is regulated by FtrC. Furthermore, we show by in vitro gel shift assays that FtrC interacts specifically with FTL_1293 mRNA and that this happens independently of the RNA chaperone Hfq. Remarkably, FtrC interacts only with full-length FTL_1293 mRNA. These results, combined with a bioinformatic analysis, indicate that FtrC interacts with the central region of the mRNA and hence does not act by sterically hindering access of the ribosome to the mRNA. We further show that gene FTL_1293 is not required for F. tularensis virulence in vitro or in vivo, which indicates that another unidentified FtrC target modulates the virulence capacity of the bacterium.
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Ramakrishnan G, Sen B, Johnson R. Paralogous outer membrane proteins mediate uptake of different forms of iron and synergistically govern virulence in Francisella tularensis tularensis. J Biol Chem 2012; 287:25191-202. [PMID: 22661710 DOI: 10.1074/jbc.m112.371856] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Francisella tularensis subsp. tularensis is a highly infectious bacterium causing acute disease in mammalian hosts. Mechanisms for the acquisition of iron within the iron-limiting host environment are likely to be critical for survival of this intracellular pathogen. FslE (FTT0025) and FupA (FTT0918) are paralogous proteins that are predicted to form β-barrels in the outer membrane of virulent strain Schu S4 and are unique to Francisella species. Previous studies have implicated both FupA, initially identified as a virulence factor and FslE, encoded by the siderophore biosynthetic operon, in iron acquisition. Using single and double mutants, we demonstrated that these paralogs function in concert to promote growth under iron limitation. We used a (55)Fe transport assay to demonstrate that FslE is involved in siderophore-mediated ferric iron uptake, whereas FupA facilitates high affinity ferrous iron uptake. Optimal replication within J774A.1 macrophage-like cells required at least one of these uptake systems to be functional. In a mouse model of tularemia, the ΔfupA mutant was attenuated, but the ΔfslE ΔfupA mutant was significantly more attenuated, implying that the two systems of iron acquisition function synergistically to promote virulence. These studies highlight the importance of specific iron acquisition functions, particularly that of ferrous iron, for virulence of F. tularensis in the mammalian host.
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Affiliation(s)
- Girija Ramakrishnan
- Department of Medicine, Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, Virginia 22901, USA.
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Abstract
The deleterious and sometimes fatal outcomes of bacterial infectious diseases are the net result of the interactions between the pathogen and the host, and the genetically tractable fruit fly, Drosophila melanogaster, has emerged as a valuable tool for modeling the pathogen-host interactions of a wide variety of bacteria. These studies have revealed that there is a remarkable conservation of bacterial pathogenesis and host defence mechanisms between higher host organisms and Drosophila. This review presents an in-depth discussion of the Drosophila immune response, the Drosophila killing model, and the use of the model to examine bacterial-host interactions. The recent introduction of the Drosophila model into the oral microbiology field is discussed, specifically the use of the model to examine Porphyromonas gingivalis-host interactions, and finally the potential uses of this powerful model system to further elucidate oral bacterial-host interactions are addressed.
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Affiliation(s)
- Christina O Igboin
- Division of Oral Biology, College of Dentistry, The Ohio State University, Columbus, Ohio, USA
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Asare R, Akimana C, Jones S, Abu Kwaik Y. Molecular bases of proliferation of Francisella tularensis in arthropod vectors. Environ Microbiol 2011. [DOI: 10.1111/j.1462-2920.2011.02651.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Dermacentor andersoni transmission of Francisella tularensis subsp. novicida reflects bacterial colonization, dissemination, and replication coordinated with tick feeding. Infect Immun 2011; 79:4941-6. [PMID: 21930762 DOI: 10.1128/iai.05676-11] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Ticks serve as biological vectors for a wide variety of bacterial pathogens which must be able to efficiently colonize specific tick tissues prior to transmission. The bacterial determinants of tick colonization are largely unknown, a knowledge gap attributed in large part to the paucity of tools to genetically manipulate these pathogens. In this study, we demonstrated that Francisella tularensis subsp. novicida, for which a complete two-allele transposon mutant library has been constructed, initially infects the midguts of 100% of acquisition-fed Dermacentor andersoni nymphs, with stable colonization and replication during a subsequent molt. Increased dissemination to and marked replication within the salivary gland was closely linked to a second (transmission) feed and culminated in secretion of bacteria into the saliva and successful transmission. Simultaneous testing of multiple mutants resulted in total bacterial levels similar to those observed for single mutants. However, there was evidence of a bottleneck during colonization, resulting in a founder effect in which the most successful mutant varied when comparing individual ticks. Thus, it is essential to assess mutant success at the level of the tick population rather than in individual ticks. The ability of F. tularensis subsp. novicida to recapitulate the key physiological events by which bacteria colonize and are transmitted by ixodid ticks provides a new genome-wide approach to identify the required pathogen molecules and pathways. The identification of specific genes and, more importantly, conserved pathways that function at the tick-pathogen interface will accelerate the development of new methods to block transmission.
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Macrophage replication screen identifies a novel Francisella hydroperoxide resistance protein involved in virulence. PLoS One 2011; 6:e24201. [PMID: 21915295 PMCID: PMC3167825 DOI: 10.1371/journal.pone.0024201] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 08/02/2011] [Indexed: 11/25/2022] Open
Abstract
Francisella tularensis is a Gram-negative facultative intracellular pathogen and the causative agent of tularemia. Recently, genome-wide screens have identified Francisella genes required for virulence in mice. However, the mechanisms by which most of the corresponding proteins contribute to pathogenesis are still largely unknown. To further elucidate the roles of these virulence determinants in Francisella pathogenesis, we tested whether each gene was required for replication of the model pathogen F. novicida within macrophages, an important virulence trait. Fifty-three of the 224 genes tested were involved in intracellular replication, including many of those within the Francisella pathogenicity island (FPI), validating our results. Interestingly, over one third of the genes identified are annotated as hypothetical, indicating that F. novicida likely utilizes novel virulence factors for intracellular replication. To further characterize these virulence determinants, we selected two hypothetical genes to study in more detail. As predicted by our screen, deletion mutants of FTN_0096 and FTN_1133 were attenuated for replication in macrophages. The mutants displayed differing levels of attenuation in vivo, with the FTN_1133 mutant being the most attenuated. FTN_1133 has sequence similarity to the organic hydroperoxide resistance protein Ohr, an enzyme involved in the bacterial response to oxidative stress. We show that FTN_1133 is required for F. novicida resistance to, and degradation of, organic hydroperoxides as well as resistance to the action of the NADPH oxidase both in macrophages and mice. Furthermore, we demonstrate that F. holarctica LVS, a strain derived from a highly virulent human pathogenic species of Francisella, also requires this protein for organic hydroperoxide resistance as well as replication in macrophages and mice. This study expands our knowledge of Francisella's largely uncharacterized intracellular lifecycle and demonstrates that FTN_1133 is an important novel mediator of oxidative stress resistance.
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Al-Khodor S, Abu Kwaik Y. Triggering Ras signalling by intracellular Francisella tularensis through recruitment of PKCα and βI to the SOS2/GrB2 complex is essential for bacterial proliferation in the cytosol. Cell Microbiol 2011; 12:1604-21. [PMID: 20618341 DOI: 10.1111/j.1462-5822.2010.01494.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Intracellular proliferation of Francisella tularensis is essential for manifestation of the fatal disease tularaemia, and is classified as a category A bioterrorism agent. The F. tularensis-containing phagosome (FCP) matures into a late endosome-like phagosome with limited fusion to lysosomes, followed by rapid bacterial escape into the cytosol. The Francisella pathogenicity island (FPI) encodes a type VI-like secretion system, and the FPI-encoded IglC is essential for evasion of lysosomal fusion and phagosomal escape. Many host signalling events are likely to be modulated by F. tularensis to render the cell permissive for intracellular proliferation but they are not fully understood. Here we show that within 15 min of infection, intracellular F. tularensis ssp. novicida triggers IglC-dependent temporal activation of Ras, but attached extracellular bacteria fail to trigger Ras activation, which has never been shown for other intracellular pathogens. Intracellular F. tularensis ssp. novicida triggers activation of Ras through recruitment of PKCα and PKCβI to the SOS2/GrB2 complex. Silencing of SOS2, GrB2 and PKCα and PKCβI by RNAi has no effect on evasion of lysosomal fusion and bacterial escape into the cytosol but renders the cytosol non-permissive for replication of F. tularensis ssp. novicida. Since Ras activation promotes cell survival, we show that silencing of SOS2, GrB2 and PKCα and βI is associated with rapid early activation of caspase-3 within 8 h post infection. However, silencing of SOS2, GrB2 and PKCα and βI does not affect phosphorylation of Akt or Erk, indicating that activation of the PI3K/Akt and the Erk signalling cascade are independent of the F. tularensis-triggered Ras activation. We conclude that intracellular F. tularensis ssp. novicida triggers temporal and early activation of Ras through the SOS2/GrB2/PKCα/PKCβI quaternary complex. Temporal and rapid trigger of Ras signalling by intracellular F. tularensis is essential for intracellular bacterial proliferation within the cytosol, and this is associated with downregulation of early caspase-3 activation.
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Affiliation(s)
- Souhaila Al-Khodor
- Department of Microbiology and Immunology, College of Medicine, Department of Biology, University of Louisville, Louisville, KY 40202, USA
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Akimana C, Kwaik YA. Francisella-arthropod vector interaction and its role in patho-adaptation to infect mammals. Front Microbiol 2011; 2:34. [PMID: 21687425 PMCID: PMC3109307 DOI: 10.3389/fmicb.2011.00034] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2010] [Accepted: 02/07/2011] [Indexed: 11/13/2022] Open
Abstract
Francisella tularensis is a Gram-negative, intracellular, zoonotic bacterium, and is the causative agent of tularemia with a broad host range. Arthropods such as ticks, mosquitoes, and flies maintain F. tularensis in nature by transmitting the bacteria among small mammals. While the tick is largely believed to be a biological vector of F. tularensis, transmission by mosquitoes and flies is largely believed to be mechanical on the mouthpart through interrupted feedings. However, the mechanism of infection of the vectors by F. tularensis is not well understood. Since F. tularensis has not been localized in the salivary gland of the primary human biting ticks, it is thought that bacterial transmission by ticks is through mechanical inoculation of tick feces containing F. tularensis into the skin wound. Drosophila melanogaster is an established good arthropod model for arthropod vectors of tularemia, where F. tularensis infects hemocytes, and is found in hemolymph, as seen in ticks. In addition, phagosome biogenesis and robust intracellular proliferation of F. tularensis in arthropod-derived cells are similar to that in mammalian macrophages. Furthermore, bacterial factors required for infectivity of mammals are often required for infectivity of the fly by F. tularensis. Several host factors that contribute to F. tularensis intracellular pathogenesis in D. melanogaster have been identified, and F. tularensis targets some of the evolutionarily conserved eukaryotic processes to enable intracellular survival and proliferation in evolutionarily distant hosts.
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Affiliation(s)
- Christine Akimana
- Department of Microbiology and Immunology, College of Medicine, University of Louisville Louisville, KY, USA
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Chong A, Celli J. The francisella intracellular life cycle: toward molecular mechanisms of intracellular survival and proliferation. Front Microbiol 2010; 1:138. [PMID: 21687806 PMCID: PMC3109316 DOI: 10.3389/fmicb.2010.00138] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Accepted: 12/05/2010] [Indexed: 11/13/2022] Open
Abstract
The tularemia-causing bacterium Francisella tularensis is a facultative intracellular organism with a complex intracellular lifecycle that ensures its survival and proliferation in a variety of mammalian cell types, including professional phagocytes. Because this cycle is essential to Francisella pathogenesis and virulence, much research has focused on deciphering the mechanisms of its intracellular survival and replication and characterizing both bacterial and host determinants of the bacterium's intracellular cycle. Studies of various strains and host cell models have led to the consensual paradigm of Francisella as a cytosolic pathogen, but also to some controversy about its intracellular cycle. In this review, we will detail major findings that have advanced our knowledge of Francisella intracellular survival strategies and also attempt to reconcile discrepancies that exist in our molecular understanding of the Francisella–phagocyte interactions.
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Affiliation(s)
- Audrey Chong
- Tularemia Pathogenesis Section, Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health Hamilton, MT, USA
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Meibom KL, Charbit A. Francisella tularensis metabolism and its relation to virulence. Front Microbiol 2010; 1:140. [PMID: 21687763 PMCID: PMC3109416 DOI: 10.3389/fmicb.2010.00140] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Accepted: 12/13/2010] [Indexed: 01/08/2023] Open
Abstract
Francisella tularensis is a Gram-negative bacterium capable of causing the zoonotic disease tularaemia in a large number of mammalian species and in arthropods. F. tularensis is a facultative intracellular bacterium that infects and replicates in vivo mainly inside macrophages. During its systemic dissemination, F. tularensis must cope with very different life conditions (such as survival in different target organs or tissues and/or survival in the blood stream…) and may thus encounter a broad variety of carbon substrates, nitrogen, phosphor, and sulfur sources, as well as very low concentrations of essential ions. The development of recent genome-wide genetic screens have led to the identification of hundreds of genes participating to variable extents to Francisella virulence. Remarkably, an important proportion of the genes identified are related to metabolic and nutritional functions. However, the relationship between nutrition and the in vivo life cycle of F. tularensis is yet poorly understood. In this review, we will address the importance of metabolism and nutrition for F. tularensis pathogenesis, focusing specifically on amino acid and carbohydrate requirements.
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Akimana C, Al-Khodor S, Abu Kwaik Y. Host factors required for modulation of phagosome biogenesis and proliferation of Francisella tularensis within the cytosol. PLoS One 2010; 5:e11025. [PMID: 20552012 PMCID: PMC2883998 DOI: 10.1371/journal.pone.0011025] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Accepted: 05/13/2010] [Indexed: 01/07/2023] Open
Abstract
Francisella tularensis is a highly infectious facultative intracellular bacterium that can be transmitted between mammals by arthropod vectors. Similar to many other intracellular bacteria that replicate within the cytosol, such as Listeria, Shigella, Burkholderia, and Rickettsia, the virulence of F. tularensis depends on its ability to modulate biogenesis of its phagosome and to escape into the host cell cytosol where it proliferates. Recent studies have identified the F. tularensis genes required for modulation of phagosome biogenesis and escape into the host cell cytosol within human and arthropod-derived cells. However, the arthropod and mammalian host factors required for intracellular proliferation of F. tularensis are not known. We have utilized a forward genetic approach employing genome-wide RNAi screen in Drosophila melanogaster-derived cells. Screening a library of approximately 21,300 RNAi, we have identified at least 186 host factors required for intracellular bacterial proliferation. We silenced twelve mammalian homologues by RNAi in HEK293T cells and identified three conserved factors, the PI4 kinase PI4KCA, the ubiquitin hydrolase USP22, and the ubiquitin ligase CDC27, which are also required for replication in human cells. The PI4KCA and USP22 mammalian factors are not required for modulation of phagosome biogenesis or phagosomal escape but are required for proliferation within the cytosol. In contrast, the CDC27 ubiquitin ligase is required for evading lysosomal fusion and for phagosomal escape into the cytosol. Although F. tularensis interacts with the autophagy pathway during late stages of proliferation in mouse macrophages, this does not occur in human cells. Our data suggest that F. tularensis utilizes host ubiquitin turnover in distinct mechanisms during the phagosomal and cytosolic phases and phosphoinositide metabolism is essential for cytosolic proliferation of F. tularensis. Our data will facilitate deciphering molecular ecology, patho-adaptation of F. tularensis to the arthropod vector and its role in bacterial ecology and patho-evolution to infect mammals.
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Affiliation(s)
- Christine Akimana
- Department of Microbiology and Immunology, College of Medicine, University of Louisville, Louisville, Kentucky, United States of America
| | - Souhaila Al-Khodor
- Department of Microbiology and Immunology, College of Medicine, University of Louisville, Louisville, Kentucky, United States of America
| | - Yousef Abu Kwaik
- Department of Microbiology and Immunology, College of Medicine, University of Louisville, Louisville, Kentucky, United States of America
- Department of Biology, University of Louisville, Louisville, Kentucky, United States of America
- * E-mail:
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Asare R, Abu Kwaik Y. Molecular complexity orchestrates modulation of phagosome biogenesis and escape to the cytosol of macrophages by Francisella tularensis. Environ Microbiol 2010; 12:2559-86. [PMID: 20482590 DOI: 10.1111/j.1462-2920.2010.02229.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Upon entry of Francisella tularensis to macrophages, the Francisella-containing phagosome (FCP) is trafficked into an acidified late endosome-like phagosome with limited fusion to the lysosomes followed by rapid escape into the cytosol where the organism replicates. Although the Francisella Pathogenicity Island (FPI), which encodes a type VI-like secretion apparatus, is required for modulation of phagosome biogenesis and escape into the cytosol, the mechanisms involved are not known. To decipher the molecular bases of modulation of biogenesis of the FCP and bacterial escape into the macrophage cytosol, we have screened a comprehensive mutant library of F. tularensis ssp. novicida for their defect in proliferation within human macrophages, followed by characterization of modulation of phagosome biogenesis and bacterial escape into the cytosol. Our data show that at least 202 genes are required for intracellular proliferation within macrophages. Among the 125 most defective mutants in intracellular proliferation, we show that the FCP of at least 91 mutants colocalize persistently with the late endosomal/lysosomal marker LAMP-1 and fail to escape into the cytosol, as determined by fluorescence-based phagosome integrity assays and transmission electron microscopy. At least 34 genes are required for proliferation within the cytosol but do not play a detectable role in modulation of phagosome biogenesis and bacterial escape into the cytosol. Our data indicate a tremendous adaptation and metabolic reprogramming by F. tularensis to adjust to the micro-environmental and nutritional cues within the FCP, and these adjustments play essential roles in modulation of phagosome biogenesis and escape into the cytosol of macrophages as well as proliferation in the cytosol. The plethora of the networks of genes that orchestrate F. tularensis-mediated modulation of phagosome biogenesis, phagosomal escape and bacterial proliferation within the cytosol is novel, complex and involves an unusually large portion of the genome of an intracellular pathogen.
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Affiliation(s)
- Rexford Asare
- Department of Microbiology and Immunology, University of Louisville College of Medicine, Louisville, KY 40292, USA
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