title: DotU and VgrG, core components of type VI secretion systems, are essential for Francisella LVS pathogenicity.
abstract: The Gram-negative bacterium Francisella tularensis causes tularemia, a disease which requires bacterial escape from phagosomes of infected macrophages. Once in the cytosol, the bacterium rapidly multiplies, inhibits activation of the inflammasome and ultimately causes death of the host cell. Of importance for these processes is a 33-kb gene cluster, the Francisella pathogenicity island (FPI), which is believed to encode a type VI secretion system (T6SS). In this study, we analyzed the role of the FPI-encoded proteins VgrG and DotU, which are conserved components of type VI secretion (T6S) clusters. We demonstrate that in F. tularensis LVS, VgrG was shown to form multimers, consistent with its suggested role as a trimeric membrane puncturing device in T6SSs, while the inner membrane protein DotU was shown to stabilize PdpB/IcmF, another T6SS core component. Upon infection of J774 cells, both ΔvgrG and ΔdotU mutants did not escape from phagosomes, and subsequently, did not multiply or cause cytopathogenicity. They also showed impaired activation of the inflammasome and marked attenuation in the mouse model. Moreover, all of the DotU-dependent functions investigated here required the presence of three residues that are essentially conserved among all DotU homologues. Thus, in agreement with a core function in T6S clusters, VgrG and DotU play key roles for modulation of the intracellular host response as well as for the virulence of F. tularensis.
authors.affiliation: Clinical Bacteriology, Department of Clinical Microbiology, and Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå, Sweden. jeanette.broms@climi.umu.se
authors.forename: Jeanette E
authors.initials: JE
authors.lastname: Bröms
authors.forename: Lena
authors.initials: L
authors.lastname: Meyer
authors.forename: Moa
authors.initials: M
authors.lastname: Lavander
authors.forename: Pär
authors.initials: P
authors.lastname: Larsson
authors.forename: Anders
authors.initials: A
authors.lastname: Sjöstedt
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005603:Francisella / Q000378:metabolism* / Q000472:pathogenicity*; D044404:Genomic Islands / Q000235:genetics / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D014409:Tumor Necrosis Factor-alpha