AEM Accepted Manuscript Posted Online 28 December 2015 Appl. Environ. Microbiol. doi:10.1128/AEM.02950-15 Copyright © 2015, American Society for Microbiology. All Rights Reserved.
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Dissection of Francisella - host cell interactions in Dictyostelium discoideum
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Elisabeth O. Lampea,b ,Yannick Brenzc, Lydia Herrmannc, Urska Repnikd, Gareth
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Griffithsd, Carl Zingmarke, Anders Sjöstedte, Hanne C. Winther-Larsena,b and
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Monica Hagedornc.
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a
Centre for Integrative Microbial Evolution (CIME) and bDepartment of
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Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway.
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c
Section Parasitology, Bernhard Nocht Institute for Tropical Medicine, Hamburg,
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Germany. dDepartment of Biosciences, University of Oslo, Oslo, Norway.
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e
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University, Umeå, Sweden.
Department of Molecular Biology, Umeå Centre for Microbial Research, Umeå
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Running title: Francisella infection in Dictyostelium
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Corresponding author: Monica Hagedorn, Bernhard Nocht Institute for Tropical
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Medicine, Bernhard-Nocht-Str. 74, 20359 Hamburg, Germany.
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Email:
[email protected]
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Y.B. and E.O.L. contributed equally to this work.
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Abstract
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Francisella bacteria cause severe disease in both vertebrates and invertebrates and
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include one of the most infectious human pathogens. Mammalian cell lines have
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mainly been used to study the mechanisms by which Francisella manipulates its host
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to replicate within a large variety of hosts and cell types, including macrophages.
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Here, we describe the establishment of a genetically and biochemically tractable
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infection model: the amoeba Dictyostelium discoideum combined with the fish
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pathogen F. noatunensis subsp noatunensis (F.n.n.). Phagocytosed F.n.n. interact
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with the endosomal pathway and escape further phagosomal maturation by
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translocating into the host cell cytosol. F.n.n. lacking IglC, a known virulence
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determinant required for Francisella intracellular replication, follows the normal
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phagosomal maturation and does not grow in Dictyostelium. The attenuation of the
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F.n.n. ΔiglC mutant was confirmed in a zebrafish embryo model, where growth of
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F.n.n. ΔiglC was restricted. In Dictyostelium, F.n.n. interacts with the autophagic
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machinery. The intracellular bacteria colocalize with autophagic markers and when
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autophagy is impaired (Dictyostelium ∆atg1) F.n.n. accumulate within Dictyostelium
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cells. Taken together, the Dictyostelium-F.n.n. infection model recapitulates the
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course of infection described in other host systems. The genetic and biochemical
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tractability of this system allows new approaches to elucidate the dynamic
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interactions between pathogenic Francisella and its host organism.
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INTRODUCTION
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The genus of Francisella comprises Gram-negative, facultative intracellular bacteria
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that infect a wide range of species, including protozoa, invertebrates and vertebrates
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(1-3). Francisella species can be divided into two lineages represented by F.
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tularensis causing potentially fatal tularemia in humans and F. noatunensis infecting
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aquatic animals (4-6). The high infectivity (
