Inner-membrane transporters for the siderophores pyochelin in Pseudomonas aeruginosa and enantio-pyochelin in Pseudomonas fluorescens display different enantioselectivities

Abstract

Iron uptake and transcriptional regulation by the enantiomeric siderophores pyochelin (Pch) and enantio-pyochelin (EPch) of Pseudomonas aeruginosa and Pseudomonas fluorescens, respectively, are stereospecific processes. The iron-loaded forms of Pch (ferriPch) and of EPch (ferriEPch) are recognized stereospecifically (i) at the outer membrane by the siderophore receptors FptA in P. aeruginosa and FetA in P. fluorescens and (ii) in the cytoplasm by the two AraC-type regulators PchR, which are activated by their cognate siderophore. Here, stereospecific siderophore recognition is shown to occur at the inner membrane also. In P. aeruginosa, translocation of ferriPch across the inner membrane is carried out by the singlesubunit siderophore transporter FptX. In contrast, the uptake of ferriEPch into the cytoplasm of P. fluorescens was found to involve a classical periplasmic binding protein-dependent ABC transporter (FetCDE), which is encoded by the fetABCDEF operon. Expression of a translational fetA-gfp fusion was repressed by ferric ions, and activated by the cognate siderophore bound to PchR, thus resembling the analogous regulation of the P. aeruginosa ferriPch transport operon fptABCX. The inner-membrane transporters FetCDE and FptX were expressed in combination with either of the two siderophore receptors FetA and FptA in a siderophore-negative P. aeruginosa mutant deleted for the fptABCX operon. Growth tests conducted under iron limitation with ferriPch or ferriEPch as the iron source revealed that FptX was able to transport ferriPch as well as ferriEPch, whereas FetCDE specifically transported ferriEPch. Thus, stereospecific siderophore recognition occurs at the inner membrane by the FetCDE transporter.

Metallome of Pseudomonas aeruginosa: a role for siderophores

“…It has since been shown that PCH has a higher affinity for Fe than previously described: 10 28.8 M −2 and 10 30.8 M −1 for PCH and PVD respectively (Albrecht-Gary et al, 1994;Brandel et al, 2012) and Fe chelation involves a stoichiometry of 1 for PVD and 2 for PCH. For the PCH pathway, the ferri-siderophore is released from the siderophore into the cytoplasm (Youard et al, 2011;Reimmann, 2012) by an unknown mechanism. The molecular mechanisms involved in iron release from siderophores in bacterial cells also differ between these two pathways (for reviews see Schalk and Guillon, 2013) and may affect the efficiency of both systems to supply P. aeruginosa cells with Fe.…”

“…Siderophore-free iron is then transported across the inner membrane by an ABC transporter (Borgna-Pignatti et al, 2006). For the PCH pathway, the ferri-siderophore is released from the siderophore into the cytoplasm (Youard et al, 2011;Reimmann, 2012) by an unknown mechanism. Moreover, PVD biosynthesis probably requires more energy than PCH biosynthesis because it involves more enzymes and precursors .…”

Chalkophores

“…Finally, pMMO itself houses a copper active site in the periplasmic portion of the PmoB subunit (55, 124), which is believed to be the final destination of most copper trafficked into methanotroph cells. For siderophores, demetalation can occur in the cytoplasm (e.g., pyochelin; 125) or the periplasm (e.g., pyoverdine; 117), and more work is needed to determine which is the better model for CuMbn copper release.…”

Disruption of Transporters Affiliated with Enantio-Pyochelin Biosynthesis Gene Cluster of Pseudomonas protegens Pf-5 Has Pleiotropic Effects

“…Recently, FetF in P . protegens CHA0 was determined not to be essential for iron-E-Pch complex uptake and is proposed to be involved in E-Pch recycling [ 21 ]. In this study, we characterized the roles of these putative transporters in E-Pch production.…”