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IglG and IglI of the Francisella pathogenicity island are important virulence determinants of Francisella tularensis LVS
Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Klinisk bakteriologi. Umeå universitet, Medicinska fakulteten, Molekylär Infektionsmedicin, Sverige (MIMS).
Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Klinisk bakteriologi. Umeå universitet, Medicinska fakulteten, Molekylär Infektionsmedicin, Sverige (MIMS).
Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Klinisk bakteriologi. Umeå universitet, Medicinska fakulteten, Molekylär Infektionsmedicin, Sverige (MIMS).
Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Klinisk bakteriologi. Umeå universitet, Medicinska fakulteten, Molekylär Infektionsmedicin, Sverige (MIMS).
2011 (Engelska)Ingår i: Infection and Immunity, ISSN 0019-9567, E-ISSN 1098-5522, Vol. 79, nr 9, s. 3683-3696Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The Gram-negative bacterium Francisella tularensis is the causative agent of tularemia, a disease intimately associated with the multiplication of the bacterium within host macrophages. This in turn requires the expression of Francisella pathogenicity island (FPI) genes, believed to encode a type VI secretion system. While the exact functions of many of the components have yet to be revealed, some have been found to contribute to the ability of Francisella to cause systemic infection in mice as well as to prevent phagolysosomal fusion and facilitate escape into the host cytosol. Upon reaching this compartment, the bacterium rapidly multiplies, inhibits activation of the inflammasome, and ultimately causes apoptosis of the host cell. In this study, we analyzed the contribution of the FPI-encoded proteins IglG, IglI, and PdpE to the aforementioned processes in F. tularensis LVS. The ΔpdpE mutant behaved similarly to the parental strain in all investigated assays. In contrast, ΔiglG and ΔiglI mutants, although they were efficiently replicating in J774A.1 cells, both exhibited delayed phagosomal escape, conferred a delayed activation of the inflammasome, and exhibited reduced cytopathogenicity as well as marked attenuation in the mouse model. Thus, IglG and IglI play key roles for modulation of the intracellular host response and also for the virulence of F. tularensis.

Ort, förlag, år, upplaga, sidor
American Society for Microbiology , 2011. Vol. 79, nr 9, s. 3683-3696
Nationell ämneskategori
Immunologi inom det medicinska området Infektionsmedicin
Identifikatorer
URN: urn:nbn:se:umu:diva-83830DOI: 10.1128/IAI.01344-10ISI: 000293891000021PubMedID: 21690239OAI: oai:DiVA.org:umu-83830DiVA, id: diva2:677398
Forskningsfinansiär
Vetenskapsrådet, 2006-3426, 2006-2877, 2009-5026Tillgänglig från: 2013-12-09 Skapad: 2013-12-09 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
Ingår i avhandling
1. The Francisella pathogenicity island: its role in type VI secretion and intracellular infection
Öppna denna publikation i ny flik eller fönster >>The Francisella pathogenicity island: its role in type VI secretion and intracellular infection
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Intracellular bacteria have developed various mechanisms to enter and persist in host cells and, at the same time, to evade the host immune response. One such pathogen is Francisella tularensis, the etiological agent of tularemia. After phagocytosis, this Gram-negative bacterium quickly escapes from the phagocytic compartment and replicates in the host cell cytosol. For this mode of infection, several components of the Francisella pathogenicity island (FPI) are critical. Interestingly, some FPI proteins share homology to components of Type VI Secretion Systems (T6SSs), but their assembly and functionality remains to be shown in Francisella.The thesis focused on the characterization of several of these FPI components; more specifically, how they contribute to the infection cycle as well as their possible role in the putative T6SS. We identified three unique mutants, ΔiglG, ΔiglI and ΔpdpE, which to various degrees were able to escape the phagosomal compartment, replicate in the host cytosol and cause host cell cytotoxicity. In contrast, ΔiglE as well as mutants within the conserved core components of T6SSs, VgrG and DotU, were defective for all of these processes. In the case of IglE, which is a lipoprotein and localized to the outer membrane of the bacterial cell wall, residues within its N-terminus were identified to be important for IglE function. Consistent with a suggested role as a trimeric membrane puncturing device, VgrG was found to form multimers. DotU stabilized the inner membrane protein IcmF, in agreement with its function as a core T6SS component. The functionality of the secretion system was shown by the translocation of several FPI proteins into the cytosol of infected macrophages, among them IglE, IglC and VgrG, of which IglE was the most prominently secreted protein. At the same time, the secretion was dependent on the core components VgrG, DotU but also on IglG. Although we and others have shown the importance of FPI proteins for the escape of F. tularensis, it has been difficult to assess their role in the subsequent replication, since mutants that fail to escape never reach the growth-permissive cytosol. For this reason, selected FPI mutants were microinjected into the cytosol of different cell types and their growth compared to their replication upon normal uptake. Our data suggest that not only the metabolic adaptation to the cytosolic compartment is important for the replication of intracytosolic bacteria, but also the mechanism of their uptake as well as the permissiveness of the cytosolic compartment per se.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2015. s. 82
Serie
Umeå University medical dissertations, ISSN 0346-6612 ; 1708
Nyckelord
Francisella, FPI, Type VI Secretion, Igl, DotU, VgrG, Pdp, microinjection, phagosomal escape, intracellular replication
Nationell ämneskategori
Mikrobiologi inom det medicinska området
Forskningsämne
klinisk bakteriologi
Identifikatorer
urn:nbn:se:umu:diva-101321 (URN)978-91-7601-246-8 (ISBN)
Disputation
2015-04-24, sal E04, byggnad 6E, NUS, Norrlands universitetssjukhus, Umeå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2015-04-01 Skapad: 2015-03-27 Senast uppdaterad: 2018-06-07Bibliografiskt granskad

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