Novel host‐specific iron acquisition system in the zoonotic pathogenVibrio vulnificus

Abstract

SummaryVibrio vulnificus is a marine bacterium associated with human and fish (mainly farmed eels) diseases globally known as vibriosis. The ability to infect and overcome eel innate immunity relies on a virulence plasmid (pVvbt2) specific for biotype 2 (Bt2) strains. In the present study, we demonstrated that pVvbt2 encodes a host-specific iron acquisition system that depends on an outer membrane receptor for eel transferrin called Vep20. The inactivation of vep20 did not affect either bacterial growth in human plasma or virulence for mice, while bacterial growth in eel blood/ plasma was abolished and virulence for eels was significantly impaired. Furthermore, vep20 is an ironregulated gene overexpressed in eel blood during artificially induced vibriosis both in vitro and in vivo. Interestingly, homologues to vep20 were identified in the transferable plasmids of two fish pathogen species of broad-host range, Vibrio harveyi (pVh1) and Photobacterium damselae subsp. damselae (pPHDD1). These data suggest that Vep20 belongs to a new family of plasmid-encoded fish-specific transferrin receptors, and the acquisition of these plasmids through horizontal gene transfer is likely positively selected in the fish-farming environment. Moreover, we propose Ftbp (fish transferrin binding proteins) as a formal name for this family of proteins.

The Fish Pathogen Vibrio vulnificus Biotype 2: Epidemiology, Phylogeny, and Virulence Factors Involved in Warm-Water Vibriosis

“…To identify the plasmid ORFs involved in virulence and serum resistance, mutants in selected ORF were obtained by allelic exchange (67,107,108). One of the selected ORFs was vep07.…”

“…In particular, vep20 shares low sequence homology (29% of amino acids identity in 220 residues) with a protein annotated as a transferrinbinding protein A precursor. The in silico analysis of Vep20 revealed a structure similar to a transferrinbinding receptor: a transmembrane protein with a TonB-dependent receptor domain, which may form a β-barrel structure, near the C-terminus and a Plug domain near the N-terminus (108). The gene also contains a Furbinding box and seems to be under Fur control (108).…”

“…The in silico analysis of Vep20 revealed a structure similar to a transferrinbinding receptor: a transmembrane protein with a TonB-dependent receptor domain, which may form a β-barrel structure, near the C-terminus and a Plug domain near the N-terminus (108). The gene also contains a Furbinding box and seems to be under Fur control (108). Mutation in vep20 increased the virulence for eels in 4 log units and abolished the ability to grow in eel blood/plasma, but did not affect the virulence for mice and the growth ability in human serum (108).…”

“…The gene also contains a Furbinding box and seems to be under Fur control (108). Mutation in vep20 increased the virulence for eels in 4 log units and abolished the ability to grow in eel blood/plasma, but did not affect the virulence for mice and the growth ability in human serum (108). The gene was overexpressed ex vivo in the eel blood/plasma, and in vivo in the blood of waterborne infected eels.…”

“…The gene was overexpressed ex vivo in the eel blood/plasma, and in vivo in the blood of waterborne infected eels. Pajuelo et al (108) obtained antibodies against Vep20 with which they demonstrated that is an OM protein of 81 kDa. Then, the authors performed binding assays between rVep20 and eel serum (albumin free) and identified the ligand by LC-MS/MS (liquid chromatography-tandem mass spectrometry) as a fish transferrin.…”