Identification of Genes, desR and desA, Required for Utilization of Desferrioxamine B as a Xenosiderophore in Vibrio furnissii

We found that Vibrio (V) furnissii ATCC35016 can gain iron through a xenosiderophore desferrioxamine B (DFOB) for its growth under iron-limiting conditions, concurrent with the expression of the 79-kDa iron-repressible outer membrane protein (I ROMP) in response to the presence of DFOB. Based on the sequence of the ferrioxamine B (an iron-bound form of DFOB) receptor gene in K vulnificus, two V furnissii genes, termed desA and desR, encoding the 79-kDa IROMP and AraC-type transcriptional regulator, respectively, were identified and cloned. Nucleotide sequences located in the promoter regions of both desR and desA predicted the presence of consensus ferric uptake regulation (Fur)-binding sequences. The transcription of both genes was negatively regulated by exogenous iron levels. Deletion of the desA gene abolished the ability of V furnissii to utilize DFOB, and neither desA mRNA nor DesA was detected in the deletion mutant of desR regardless of the presence of DFOB. The functions of DesA and DesR as the ferrioxamine B receptor and transcriptional activator for desA, respectively, were confirmed by complementation of desA and desR deletion mutants.