The FupA/B protein uniquely facilitates transport of ferrous iron and siderophore-associated ferric iron across the outer membrane of Francisella tularensis live vaccine strain

Ramakrishnan, Girija; Sen, Bhaswati

doi:10.1099/mic.0.072835-0

Cited by 20 publications

(46 citation statements)

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“…A recent study demonstrated that the siderophore system and the Feo system are the sole iron uptake mechanisms in LVS [5]. In line with this, the results of the present study show that the utilisation of heme by SCHU S4 also relies on these two systems.…”

Section: Discussionsupporting

confidence: 90%

Mechanisms of Heme Utilization by Francisella tularensis

et al. 2015

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Francisella tularensis is a highly virulent facultative intracellular pathogen causing the severe disease tularemia in mammals. As for other bacteria, iron is essential for its growth but very few mechanisms for iron acquisition have been identified. Here, we analyzed if and how F. tularensis can utilize heme, a major source of iron in vivo. This is by no means obvious since the bacterium lacks components of traditional heme-uptake systems. We show that SCHU S4, the prototypic strain of subspecies tularensis, grew in vitro with heme as the sole iron source. By screening a SCHU S4 transposon insertion library, 16 genes were identified as important to efficiently utilize heme, two of which were required to avoid heme toxicity. None of the identified genes appeared to encode components of a potential heme-uptake apparatus. Analysis of SCHU S4 deletion mutants revealed that each of the components FeoB, the siderophore system, and FupA, contributed to the heme-dependent growth. In the case of the former two systems, iron acquisition was impaired, whereas the absence of FupA did not affect iron uptake but led to abnormally high binding of iron to macromolecules. Overall, the present study demonstrates that heme supports growth of F. tularensis and that the requirements for the utilization are highly complex and to some extent novel.

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Section: Discussionsupporting

confidence: 90%

Mechanisms of Heme Utilization by Francisella tularensis

et al. 2015

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“…We compared the ability of the Δ feoB ′ and wild-type LVS strains to take up 55 Fe 2+ at two iron concentrations, 0.1 μM for high affinity iron acquisition and 3 μM reflecting low affinity transport [19]. Bacterial strains were grown overnight under iron-limitation and were then incubated with 55 Fe in the presence of ascorbate to keep the iron in the reduced form.…”

Section: Resultsmentioning

confidence: 99%

The Reduced Genome of the Francisella tularensis Live Vaccine Strain (LVS) Encodes Two Iron Acquisition Systems Essential for Optimal Growth and Virulence

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Ramakrishnan

2014

PLoS ONE

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Bacterial pathogens require multiple iron-specific acquisition systems for survival within the iron-limiting environment of the host. Francisella tularensis is a virulent intracellular pathogen that can replicate in multiple cell-types. To study the interrelationship of iron acquisition capability and virulence potential of this organism, we generated single and double deletion mutants within the ferrous iron (feo) and ferric-siderophore (fsl) uptake systems of the live vaccine strain (LVS). The Feo system was disrupted by a partial deletion of the feoB gene (ΔfeoB′), which led to a growth defect on iron-limited modified Muller Hinton agar plates. 55Fe uptake assays verified that the ΔfeoB′ mutant had lost the capacity for ferrous iron uptake but was still competent for 55Fe-siderophore-mediated ferric iron acquisition. Neither the ΔfeoB′ nor the siderophore-deficient ΔfslA mutant was defective for replication within J774A.1 murine macrophage-like cells, thus demonstrating the ability of LVS to survive using either ferrous or ferric sources of intracellular iron. A LVS ΔfslA ΔfeoB′ mutant defective for both ferrous iron uptake and siderophore production was isolated in the presence of exogenous F. tularensis siderophore. In contrast to the single deletion mutants, the ΔfslA ΔfeoB′ mutant was unable to replicate within J774A.1 cells and was attenuated in virulence following intraperitoneal infection of C57BL/6 mice. These studies demonstrate that the siderophore and feoB-mediated ferrous uptake systems are the only significant iron acquisition systems in LVS and that they operate independently. While one system can compensate for loss of the other, both are required for optimal growth and virulence.

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“…Both proteins have been localized to the outer membrane of F. tularensis (Huntley et al, 2007; Ramakrishnan and Sen, 2014) and share a global 54% identity and 69% similarity in amino acid sequence. FupA with 557 amino acid residues is larger than FslE (509 residues).…”

Section: Introductionmentioning

confidence: 99%

“…Infrequent recombinational deletion events have been observed leading to formation of fupA/B hybrid genes (Twine et al, 2005; Rohmer et al, 2006); such recombination accounts for a significant reduction in virulence as seen in LVS, which can be reversed by restoration of the full length fupA gene (Salomonsson et al, 2009). The FupA/B hybrid protein encoded by LVS is less efficient at high-affinity ferrous iron uptake than FupA, but gains siderophore-iron uptake capability (Sen et al, 2010; Ramakrishnan and Sen, 2014). The structural and functional overlap in protein function raises the intriguing possibility that a common mechanism may underlie transport by FslE and FupA.…”

Section: Introductionmentioning

confidence: 99%

Iron and Virulence in Francisella tularensis

Ramakrishnan

2017

Front. Cell. Infect. Microbiol.

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Francisella tularensis, the causative agent of tularemia, is a Gram-negative bacterium that infects a variety of cell types including macrophages, and propagates with great efficiency in the cytoplasm. Iron, essential for key enzymatic and redox reactions, is among the nutrients required to support this pathogenic lifestyle and the bacterium relies on specialized mechanisms to acquire iron within the host environment. Two distinct pathways for iron acquisition are encoded by the F. tularensis genome- a siderophore-dependent ferric iron uptake system and a ferrous iron transport system. Genes of the Fur-regulated fslABCDEF operon direct the production and transport of the siderophore rhizoferrin. Siderophore biosynthesis involves enzymes FslA and FslC, while export across the inner membrane is mediated by FslB. Uptake of the rhizoferrin- ferric iron complex is effected by the siderophore receptor FslE in the outer membrane in a TonB-independent process, and FslD is responsible for uptake across the inner membrane. Ferrous iron uptake relies largely on high affinity transport by FupA in the outer membrane, while the Fur-regulated FeoB protein mediates transport across the inner membrane. FslE and FupA are paralogous proteins, sharing sequence similarity and possibly sharing structural features as well. This review summarizes current knowledge of iron acquisition in this organism and the critical role of these uptake systems in bacterial pathogenicity.

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The FupA/B protein uniquely facilitates transport of ferrous iron and siderophore-associated ferric iron across the outer membrane of Francisella tularensis live vaccine strain

Cited by 20 publications

References 29 publications

Mechanisms of Heme Utilization by Francisella tularensis

Mechanisms of Heme Utilization by Francisella tularensis

The Reduced Genome of the Francisella tularensis Live Vaccine Strain (LVS) Encodes Two Iron Acquisition Systems Essential for Optimal Growth and Virulence

Iron and Virulence in Francisella tularensis

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