Catechol Siderophore Transport by Vibrio cholerae

ABSTRACTSiderophores, small iron-binding molecules secreted by many microbial species, capture environmental iron for transport back into the cell.Vibrio choleraesynthesizes and uses the catechol siderophore vibriobactin and also uses siderophores secreted by other species, including enterobactin produced byEscherichia coli.E. colisecretes both canonical cyclic enterobactin and linear enterobactin derivatives likely derived from its cleavage by the enterobactin esterase Fes. We show here thatV. choleraedoes not use cyclic enterobactin but instead uses its linear derivatives.V. choleraelacked both a receptor for efficient transport of cyclic enterobactin and enterobactin esterase to promote removal of iron from the ferrisiderophore complex. To further characterize the transport of catechol siderophores, we show that the linear enterobactin derivatives were transported intoV. choleraeby either of the catechol siderophore receptors IrgA and VctA, which also transported the synthetic siderophore MECAM [1,3,5-N,N′,N″-tris-(2,3-dihydroxybenzoyl)-triaminomethylbenzene]. Vibriobactin is transported via the additional catechol siderophore receptor ViuA, while theVibrio fluvialissiderophore fluvibactin was transported by all three catechol receptors. ViuB, a putativeV. choleraesiderophore-interacting protein (SIP), functionally substituted for theE. coliferric reductase YqjH, which promotes the release of iron from the siderophore in the bacterial cytoplasm. InV. cholerae, ViuB was required for the use of vibriobactin but was not required for the use of MECAM, fluvibactin, ferrichrome, or the linear derivatives of enterobactin. This suggests the presence of another protein inV. choleraecapable of promoting the release of iron from these siderophores.IMPORTANCEVibrio choleraeis a major human pathogen and also serves as a model for theVibrionaceae, which include other serious human and fish pathogens. The ability of these species to persist and acquire essential nutrients, including iron, in the environment is epidemiologically important but not well understood. In this work, we characterize the ability ofV. choleraeto acquire iron by using siderophores produced by other organisms. We resolve confusion in the literature regarding its ability to use theEscherichia colisiderophore enterobactin and identify the receptor and TonB system used for the transport of several siderophores. The use of some siderophores did not require the ferric reductase ViuB, suggesting that an uncharacterized ferric reductase is present inV. cholerae.

Transcription Termination within the Iron Transport-Biosynthesis Operon of Vibrio anguillarum Requires an Antisense RNA

ABSTRACT The iron transport-biosynthesis (ITB) operon in Vibrio anguillarum includes four genes for ferric siderophore transport, fatD, -C, -B, and -A, and two genes for siderophore biosynthesis, angR and angT. This cluster plays an important role in the virulence mechanisms of this bacterium. Despite being part of the same polycistronic mRNA, the relative levels of transcription for the fat portion and for the whole ITB message differ profoundly, the levels of the fat transcript being about 17-fold higher. Using S1 nuclease mapping, lacZ transcriptional fusions, and in vitro studies, we were able to show that the differential gene expression within the ITB operon is due to termination of transcription between the fatA and angR genes, although a few transcripts proceeded beyond the termination site to the end of this operon. This termination process requires a 427-nucleotide antisense RNA that spans the intergenic region and acts as a novel transcriptional terminator.