Pseudomonas aeruginosa is an opportunistic pathogen, synthesizing two major siderophores, pyoverdine (Pvd) and pyochelin (Pch), to cover its needs in iron(III). If the high affinity and specificity of Pvd toward iron(III) (pFe = 27.0) was well described in the literature, the physicochemical and coordination properties of Pch toward biologically relevant metals (Fe(III), Cu(II) or Zn(II)) have been only scarcely investigated. We report a thorough physico-chemical investigation of Pch (potentiometry, spectrophotometries, ESI/MS) that highlighted its moderate but significantly higher affinity for Fe³⁺ (pFe = 16.0 at p[H] 7.4) than reported previously. We also demonstrated that Pch strongly chelates divalent metals such as Zn(II) (pZn = 11.8 at p[H] 7.4) and Cu(II) (pCu = 14.9 at p[H] 7.4) and forms predominantly 1 : 2 (M²⁺/Pch) complexes. Kinetic studies revealed that the formation of the ferric Pch complexes proceeds through a Eigen-Wilkins dissociative ligand interchange mechanism involving two protonated species of Pch and the Fe(OH)²⁺ species of Fe(III). Our physico-chemical parameters supports the previous biochemical studies which proposed that siderophores are not only devoted to iron(III) shuttling but most likely display other specific biological role in the subtle metals homeostasis in microorganisms. This work also represents a step toward deciphering the role of siderophores throughout evolution.

Bacteria use small molecules called siderophores to scavenge iron. Siderophore-Fe³⁺complexes are recognised by outer-membrane transporters and imported into the periplasm in a process dependent on the inner-membrane protein TonB. The siderophore enterobactin is secreted by members of the family Enterobacteriaceae, but many other bacteria includingPseudomonasspecies can use it. Here, we show that thePseudomonastransporter PfeA recognises enterobactin using extracellular loops distant from the pore. The relevance of this site is supported by in vivo and in vitro analyses. We suggest there is a second binding site deeper inside the structure and propose that correlated changes in hydrogen bonds link binding-induced structural re-arrangements to the structural adjustment of the periplasmic TonB-binding motif.

Pyochelin is a siderophore common to Pseudomonas aeruginosa and several other pathogenic bacteria. A pyochelin functionalized at the N3′′ position with a propyl-amine extension was previously synthesized. In the present work we proved that this analog binds FptA, the pyochelin outer membrane receptor, and transports iron(III) efficiently into bacteria. This functionalized pyochelin seemed to be a good candidate for antibiotic vectorization in the framework of a Trojan horse prodrug strategy. In this context, conjugates between pyochelin and three fluoroquinolones (norfloxacin, ciprofloxacin and N-desmethyl-ofloxacin) were synthesized with a spacer arm that was either stable or hydrolyzable in vivo. Some pyochelin–fluoroquinolone conjugates had antibacterial activities in growth inhibition experiments on several P. aeruginosa strains. However, these activities were weaker than those of the antibiotic alone. These properties appeared to be related to both the solubility and bioavailability of conjugates and to the stability of the spacer arm used.

Aspergillus fumigatus and Pseudomonas aeruginosa are central fungal and bacterial members of the pulmonary microbiota. The interactions between A. fumigatus and P. aeruginosa have only just begun to be explored. A balance between inhibitory and stimulatory effects on fungal growth was observed in mixed A. fumigatus–P. aeruginosa cultures. Negative interactions have been seen for homoserine-lactones, pyoverdine and pyochelin resulting from iron starvation and intracellular inhibitory reactive oxidant production. In contrast, several types of positive interactions were recognized. Dirhamnolipids resulted in the production of a thick fungal cell wall, allowing the fungus to resist stress. Phenazines and pyochelin favor iron uptake for the fungus. A. fumigatus is able to use bacterial volatiles to promote its growth. The immune response is also differentially regulated by co-infections.

Siderophores are small metal chelators synthesized by numerous organisms to access iron. These secondary metabolites are ubiquitously present on Earth, and because their production represents the main strategy to assimilate iron, they play an important role in both positive and negative interactions between organisms. In addition, siderophores are used in biotechnology for diverse applications in medicine, agriculture and the environment. The generation of non-natural siderophore analogs provides a new opportunity to create new-to-nature chelating biomolecules that can offer new properties to expand applications. This review summarizes the main strategies of combinatorial biosynthesis that have been used to generate siderophore analogs. We first provide a brief overview of siderophore biosynthesis, followed by a description of the strategies, namely, precursor-directed biosynthesis, the design of synthetic or heterologous pathways and enzyme engineering, used in siderophore biosynthetic pathways to create diversity. In addition, this review highlights the engineering strategies that have been used to improve the production of siderophores by cells to facilitate their downstream utilization.

Pseudomonas aeruginosa is a Gram-negative pathogenic bacterium responsible for severe infections in which resistance to most of the approved families of antibiotics is increasing. Oxazolidinone antibiotics are active against many Gram-positive bacteria, but are only weakly active against Gram-negative pathogens. We describe the synthesis of conjugates between a catechol moiety and oxazolidinone antibiotics. These conjugates were significantly more active against P. aeruginosa (218–1024 μM) than linezolid (MIC > 1024 μM), the reference molecule from the oxazolidinone family. Antibiotic activity was slightly higher in medium depleted of iron, suggesting the involvement of a bacterial iron uptake system in this biological activity. The bacterial iron uptake pathway involved in the transport is still to be addressed, but the present data excluded a contribution of the enterobactin transporter PfeA.