Pseudomonas fluorescens CHA0 Produces Enantio-pyochelin, the Optical Antipode of the Pseudomonas aeruginosa Siderophore Pyochelin

Abstract

The siderophore pyochelin is made by a thiotemplate mechanism from salicylate and two molecules of cysteine. In Pseudomonas aeruginosa, the first cysteine residue is converted to its D-isoform during thiazoline ring formation whereas the second cysteine remains in its L-configuration, thus determining the stereochemistry of the two interconvertible pyochelin diastereoisomers as 4R,2؆R,4؆R (pyochelin I) and 4R,2؆S,4؆R (pyochelin II). Pseudomonas fluorescens CHA0 was found to make a different stereoisomeric mixture, which promoted growth under iron limitation in strain CHA0 and induced the expression of its biosynthetic genes, but was not recognized as a siderophore and signaling molecule by P. aeruginosa. Reciprocally, pyochelin promoted growth and induced pyochelin gene expression in P. aeruginosa, but was not functional in P. fluorescens. The structure of the CHA0 siderophore was determined by mass spectrometry, thin-layer chromatography, NMR, polarimetry, and chiral HPLC as enantio-pyochelin, the optical antipode of the P. aeruginosa siderophore pyochelin. Enantio-pyochelin was chemically synthesized and confirmed to be active in CHA0. Its potential biosynthetic pathway in CHA0 is discussed.

The plant pathogen Streptomyces scabies 87-22 has a functional pyochelin biosynthetic pathway that is regulated by TetR- and AfsR-family proteins

“…Deletion of the SCAB1471 gene in the DSCAB1401 mutant abrogated production of the metabolite, confirming that it is a product of the PBGC. LC-MS analyses on a homochiral stationary phase confirmed that S. scabies produces pyochelin and not ent-pyochelin, consistent with the presence of a pchG orthologue (SCAB1461) and the absence of a pchK orthologue in the PBGC, as well as the presence of a putative methyl transferase-like epimerization domain in the PchE orthologue SCAB1481 (Youard et al, 2007).…”

“…S1, available with the online version of this paper). The recent report of the isolation of ent-pyochelin from P. fluorescens prompted us to analyse the stereochemistry of pyochelin produced by S. scabies (Youard et al, 2007). Culture supernatants of the DSCAB1401 mutant were compared by LC-MS on a homochiral stationary phase with synthetic standards of pyochelin and ent-pyochelin (Youard et al, 2007).…”

Stereospecific recognition of pyochelin and enantio-pyochelin by the PchR proteins in fluorescent pseudomonads

“…1; Youard et al, 2007). Enantio-pyochelin was found to promote growth of P. fluorescens under iron limitation and to upregulate its own biosynthesis genes in a manner similar to that of pyochelin in P. aeruginosa (Youard et al, 2007). However, enantio-pyochelin does not promote growth of P. aeruginosa and pyochelin has no such activity in P. fluorescens (Youard et al, 2007).…”

“…1; Youard et al, 2007). Enantio-pyochelin was found to promote growth of P. fluorescens under iron limitation and to upregulate its own biosynthesis genes in a manner similar to that of pyochelin in P. aeruginosa (Youard et al, 2007).…”

“…Addition of enantiopyochelin to P. aeruginosa cultures does not induce the expression of the pyochelin biosynthesis genes and addition of pyochelin to P. fluorescens cultures hardly induces the expression of the enantio-pyochelin biosynthesis genes (Youard et al, 2007). It has not been clear, however, if this stereospecificity in signalling might be caused simply by the failure of FptA and FetA to internalize the siderophore of the other species, thereby preventing the activation of the PchR regulatory protein, or whether additionally the PchR protein might not be activated by the siderophore of the other species.…”