The Fish Pathogen Vibrio ordalii Under Iron Deprivation Produces the Siderophore Piscibactin

Abstract

<i>Vibrio ordalii</i> is the causative agent of vibriosis, mainly in salmonid fishes, and its virulence mechanisms are still not completely understood. In previous works we demonstrated that <i>V. ordalii</i> possess several iron uptake mechanisms based on heme utilization and siderophore production. The aim of the present work was to confirm the production and utilization of piscibactin as a siderophore by <i>V. ordalii</i>. Using genetic analysis, identification by peptide mass fingerprinting (PMF) of iron-regulated membrane proteins and chemical identification by LC-HRMS, we were able to clearly demonstrate that <i>V. ordalii</i> produces piscibactin under iron limitation. The synthesis and transport of this siderophore is encoded by a chromosomal gene cluster homologous to another one described in <i>V. anguillarum</i>, which also encodes the synthesis of piscibactin. Using β-galactosidase assays we were able to show that two potential promoters regulated by iron control the transcription of this gene cluster in <i>V. ordalii</i>. Moreover, biosynthetic and transport proteins corresponding to piscibactin synthesis and uptake could be identified in membrane fractions of <i>V. ordalii</i> cells grown under iron limitation. The synthesis of piscibactin was previously reported in other fish pathogens like <i>Photobacterium damselae</i> subsp. <i>piscicida</i> and <i>V. anguillarum</i>, which highlights the importance of this siderophore as a key virulence factor in Vibrionaceae bacteria infecting poikilothermic animals.