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Cantlay S, Kaftanic C, Horzempa J. PdpC, a secreted effector protein of the type six secretion system, is required for erythrocyte invasion by Francisella tularensis LVS. Front Cell Infect Microbiol 2022; 12:979693. [PMID: 36237421 PMCID: PMC9552824 DOI: 10.3389/fcimb.2022.979693] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 09/02/2022] [Indexed: 12/01/2022] Open
Abstract
Francisella tularensis is a gram negative, intracellular pathogen that is the causative agent of the potentially fatal disease, tularemia. During infection, F. tularensis is engulfed by and replicates within host macrophages. Additionally, this bacterium has also been shown to invade human erythrocytes and, in both cases, the Type Six Secretion System (T6SS) is required for these host-pathogen interaction. One T6SS effector protein, PdpC, is important for macrophage infection, playing a role in phagolysosomal escape and intracellular replication. To determine if PdpC also plays a role in erythrocyte invasion, we constructed a pdpC-null mutant in the live vaccine strain, F. tularensis LVS. We show that PdpC is required for invasion of human and sheep erythrocytes during in vitro assays and that reintroduction of a copy of pdpC, in trans, rescues this phenotype. The interaction with human erythrocytes was further characterized using double-immunofluorescence microscopy to show that PdpC is required for attachment of F. tularensis LVS to erythrocytes as well as invasion. To learn more about the role of PdpC in erythrocyte invasion we generated a strain of F. tularensis LVS expressing pdpC-emgfp. PdpC-EmGFP localizes as discrete foci in a subset of F. tularensis LVS cells grown in broth culture and accumulates in erythrocytes during invasion assays. Our results are the first example of a secreted effector protein of the T6SS shown to be involved in erythrocyte invasion and indicate that PdpC is secreted into erythrocytes during invasion.
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Affiliation(s)
| | | | - Joseph Horzempa
- Department of Biological Sciences, West Liberty University, West Liberty, WV, United States
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Schmitt DM, Barnes R, Rogerson T, Haught A, Mazzella LK, Ford M, Gilson T, Birch JWM, Sjöstedt A, Reed DS, Franks JM, Stolz DB, Denvir J, Fan J, Rekulapally S, Primerano DA, Horzempa J. The Role and Mechanism of Erythrocyte Invasion by Francisella tularensis. Front Cell Infect Microbiol 2017; 7:173. [PMID: 28536678 PMCID: PMC5423315 DOI: 10.3389/fcimb.2017.00173] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 04/21/2017] [Indexed: 01/06/2023] Open
Abstract
Francisella tularensis is an extremely virulent bacterium that can be transmitted naturally by blood sucking arthropods. During mammalian infection, F. tularensis infects numerous types of host cells, including erythrocytes. As erythrocytes do not undergo phagocytosis or endocytosis, it remains unknown how F. tularensis invades these cells. Furthermore, the consequence of inhabiting the intracellular space of red blood cells (RBCs) has not been determined. Here, we provide evidence indicating that residing within an erythrocyte enhances the ability of F. tularensis to colonize ticks following a blood meal. Erythrocyte residence protected F. tularensis from a low pH environment similar to that of gut cells of a feeding tick. Mechanistic studies revealed that the F. tularensis type VI secretion system (T6SS) was required for erythrocyte invasion as mutation of mglA (a transcriptional regulator of T6SS genes), dotU, or iglC (two genes encoding T6SS machinery) severely diminished bacterial entry into RBCs. Invasion was also inhibited upon treatment of erythrocytes with venom from the Blue-bellied black snake (Pseudechis guttatus), which aggregates spectrin in the cytoskeleton, but not inhibitors of actin polymerization and depolymerization. These data suggest that erythrocyte invasion by F. tularensis is dependent on spectrin utilization which is likely mediated by effectors delivered through the T6SS. Our results begin to elucidate the mechanism of a unique biological process facilitated by F. tularensis to invade erythrocytes, allowing for enhanced colonization of ticks.
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Affiliation(s)
- Deanna M Schmitt
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Rebecca Barnes
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Taylor Rogerson
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Ashley Haught
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Leanne K Mazzella
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Matthew Ford
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Tricia Gilson
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - James W-M Birch
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
| | - Anders Sjöstedt
- Department of Clinical Microbiology, Clinical Bacteriology, and Laboratory for Molecular Infection Medicine Sweden, Umeå UniversityUmeå, Sweden
| | - Douglas S Reed
- Regional Biocontainment Laboratory, Center for Vaccine Research, University of PittsburghPittsburgh, PA, USA
| | - Jonathan M Franks
- Center for Biologic Imaging, University of Pittsburgh School of MedicinePittsburgh, PA, USA
| | - Donna B Stolz
- Center for Biologic Imaging, University of Pittsburgh School of MedicinePittsburgh, PA, USA
| | - James Denvir
- Department of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall UniversityHuntington, WV, USA
| | - Jun Fan
- Department of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall UniversityHuntington, WV, USA
| | - Swanthana Rekulapally
- Department of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall UniversityHuntington, WV, USA
| | - Donald A Primerano
- Department of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall UniversityHuntington, WV, USA
| | - Joseph Horzempa
- Department of Natural Sciences and Mathematics, West Liberty UniversityWest Liberty, WV, USA
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Horzempa J, O'Dee DM, Stolz DB, Franks JM, Clay D, Nau GJ. Invasion of erythrocytes by Francisella tularensis. J Infect Dis 2011; 204:51-9. [PMID: 21628658 DOI: 10.1093/infdis/jir221] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Francisella tularensis is the causative agent of tularemia and is classified as a category A biodefense agent by the Centers for Disease Control and Prevention because of its highly infectious nature. F. tularensis infects leukocytes and exhibits an extracellular phase in the blood of the host. It is unknown, however, whether F. tularensis can infect erythrocytes; thus, we examined this possibility in vivo and in vitro. In the murine model of pulmonary type A tularemia, we showed the presence of intraerythrocytic bacteria by double-immunofluorescence microscopy and ex vivo gentamicin protection of the purified erythrocyte fraction. In vitro, F. tularensis invaded human erythrocytes, as shown in the gentamicin protection assays, double-immunofluorescence microscopy, flow cytometry, scanning electron microscopy, and transmission electron microscopy with immunogold labeling of the bacteria. Additional in vitro tests indicated that serum complement-dependent and complement-independent mechanisms contribute to erythrocyte invasion. Our results reveal a novel intraerythrocytic phase during F. tularensis infection.
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Affiliation(s)
- Joseph Horzempa
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, PA, USA
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Dai J, Wang P, Adusumilli S, Booth CJ, Narasimhan S, Anguita J, Fikrig E. Antibodies against a tick protein, Salp15, protect mice from the Lyme disease agent. Cell Host Microbe 2010; 6:482-92. [PMID: 19917502 DOI: 10.1016/j.chom.2009.10.006] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2009] [Revised: 08/31/2009] [Accepted: 10/09/2009] [Indexed: 11/24/2022]
Abstract
Traditionally, vaccines directly target a pathogen or microbial toxin. Lyme disease, caused by Borrelia burgdorferi, is a tick-borne illness for which a human vaccine is not currently available. B. burgdorferi binds a tick salivary protein, Salp15, during transmission from the vector, and this interaction facilitates infection of mice. We now show that Salp15 antiserum significantly protected mice from B. burgdorferi infection. Salp15 antiserum also markedly enhanced the protective capacity of antibodies against B. burgdorferi antigens, such as OspA or OspC. Mice actively immunized with Salp15 were also significantly protected from tick-borne Borrelia. In vitro assays showed that Salp15 antiserum increased the clearance of Salp15-coated B. burgdorferi by phagocytes, suggesting a mechanism of action. Vaccination with a vector molecule that a microbe requires for infection of the mammalian host suggests a new strategy for the prevention of Lyme disease, and this paradigm may be applicable to numerous arthropod-borne pathogens of medical importance.
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Affiliation(s)
- Jianfeng Dai
- Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA
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