The natural alternative: protozoa as cellular models for<i>L</i><i>egionella</i>infection

Hoffmann, Christine; Harrison, Christopher F.; Hilbi, Hubert

doi:10.1111/cmi.12235

Cited by 110 publications

(85 citation statements)

References 128 publications

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“…For example, IglC is essential for Francisella survival and growth in both systems (49). A similar principle is conserved in Legionella infections (50).…”

mentioning

confidence: 97%

Dissection of Francisella-Host Cell Interactions in Dictyostelium discoideum

Lampe

Brenz

Herrmann

et al. 2016

Appl Environ Microbiol

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f Francisella bacteria cause severe disease in both vertebrates and invertebrates and include one of the most infectious human pathogens. Mammalian cell lines have mainly been used to study the mechanisms by which Francisella manipulates its host to replicate within a large variety of hosts and cell types, including macrophages. Here, we describe the establishment of a genetically and biochemically tractable infection model: the amoeba Dictyostelium discoideum combined with the fish pathogen Francisella noatunensis subsp. noatunensis. Phagocytosed F. noatunensis subsp. noatunensis interacts with the endosomal pathway and escapes further phagosomal maturation by translocating into the host cell cytosol. F. noatunensis subsp. noatunensis lacking IglC, a known virulence determinant required for Francisella intracellular replication, follows the normal phagosomal maturation and does not grow in Dictyostelium. The attenuation of the F. noatunensis subsp. noatunensis ⌬iglC mutant was confirmed in a zebrafish embryo model, where growth of F. noatunensis subsp. noatunensis ⌬iglC was restricted. In Dictyostelium, F. noatunensis subsp. noatunensis interacts with the autophagic machinery. The intracellular bacteria colocalize with autophagic markers, and when autophagy is impaired (Dictyostelium ⌬atg1), F. noatunensis subsp. noatunensis accumulates within Dictyostelium cells. Altogether, the Dictyostelium-F. noatunensis subsp. noatunensis infection model recapitulates the course of infection described in other host systems. The genetic and biochemical tractability of the system allows new approaches to elucidate the dynamic interactions between pathogenic Francisella and its host organism.

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“…For example, IglC is essential for Francisella survival and growth in both systems (49). A similar principle is conserved in Legionella infections (50).…”

mentioning

confidence: 97%

Dissection of Francisella-Host Cell Interactions in Dictyostelium discoideum

Lampe

Brenz

Herrmann

et al. 2016

Appl Environ Microbiol

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“…Predominantly, however, Legionella spp. parasitize free-living protozoa and grow within these unicellular bacterivores (4,5). When bacteria-laden aerosols are inhaled, L. pneumophila reaches the lung, where the opportunistic pathogen infects and replicates within alveolar macrophages (6).…”

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confidence: 99%

Metabolism of myo -Inositol by Legionella pneumophila Promotes Infection of Amoebae and Macrophages

Manske

Schell

Hilbi

2016

Appl Environ Microbiol

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Legionella pneumophila is a natural parasite of environmental amoebae and the causative agent of a severe pneumonia termed Legionnaires' disease. The facultative intracellular pathogen employs a bipartite metabolism, where the amino acid serine serves as the major energy supply, while glycerol and glucose are mainly utilized for anabolic processes. The L. pneumophila genome harbors the cluster lpg1653 to lpg1649 putatively involved in the metabolism of the abundant carbohydrate myo-inositol (here termed inositol). To assess inositol metabolism by L. pneumophila, we constructed defined mutant strains lacking lpg1653 or lpg1652, which are predicted to encode the inositol transporter IolT or the inositol-2-dehydrogenase IolG, respectively. The mutant strains were not impaired for growth in complex or defined minimal media, and inositol did not promote extracellular growth. However, upon coinfection of Acanthamoeba castellanii, the mutants were outcompeted by the parental strain, indicating that the intracellular inositol metabolism confers a fitness advantage to the pathogen. Indeed, inositol added to L. pneumophila-infected amoebae or macrophages promoted intracellular growth of the parental strain, but not of the ⌬iolT or ⌬iolG mutant, and growth stimulation by inositol was restored by complementation of the mutant strains. The expression of the P iol promoter and bacterial uptake of inositol required the alternative sigma factor RpoS, a key virulence regulator of L. pneumophila. Finally, the parental strain and ⌬iolG mutant bacteria but not the ⌬iolT mutant strain accumulated [U-14 C 6 ]inositol, indicating that IolT indeed functions as an inositol transporter. Taken together, intracellular L. pneumophila metabolizes inositol through the iol gene products, thus promoting the growth and virulence of the pathogen. IMPORTANCEThe environmental bacterium Legionella pneumophila is the causative agent of a severe pneumonia termed Legionnaires' disease. The opportunistic pathogen replicates in protozoan and mammalian phagocytes in a unique vacuole. Amino acids are thought to represent the prime source of carbon and energy for L. pneumophila. However, genome, transcriptome, and proteome studies indicate that the pathogen not only utilizes amino acids as carbon sources but possesses broader metabolic capacities. In this study, we analyzed the metabolism of inositol by extra-and intracellularly growing L. pneumophila. By using genetic, biochemical, and cell biological approaches, we found that L. pneumophila accumulates and metabolizes inositol through the iol gene products, thus promoting the intracellular growth, virulence, and fitness of the pathogen. Our study significantly contributes to an understanding of the intracellular niche of a human pathogen. L egionella pneumophila is a Gram-negative ubiquitous environmental bacterium that survives in complex multispecies biofilms in natural or manmade water sources (1-3). Predominantly, however, Legionella spp. parasitize free-living protozoa and grow within these u...

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“…The environmental niches, transmission route, and disease epidemiology of L. longbeachae and L. pneumophila differ considerably (5). L. longbeachae is associated with compost and potting soils (3,6), whereas L. pneumophila is found ubiquitously in natural and man-made water systems (7,8). The preferences of the Legionella spp.…”

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confidence: 99%