Different iron-chelating properties of pyochelin diastereoisomers revealed by LC/MS

Structure of the Outer Membrane Transporter FemA and Its Role in the Uptake of Ferric Dihydro-Aeruginoic Acid and Ferric Aeruginoic Acid in Pseudomonas aeruginosa

Iron is essential for bacterial growth, and Pseudomonas aeruginosa synthesizes the siderophores pyochelin (PCH) and pyoverdine to acquire it. PCH contains a thiazolidine ring that aids in iron chelation but is prone to hydrolysis, leading to the formation of 2-(2-hydroxylphenyl)-thiazole-4-carbaldehyde (IQS). Using mass spectrometry, we demonstrated that PCH undergoes hydrolysis and oxidation in solution, resulting in the formation of aeruginoic acid (AA). This study used proteomic analyses and fluorescent reporters to show that AA, dihydroaeruginoic acid (DHA), and PCH induce the expression of femA, a gene encoding the ferri-mycobactin outer membrane transporter in P. aeruginosa. Notably, the induction by AA and DHA was observed only in strains unable to produce pyoverdine, suggesting their weaker iron-chelating ability compared to that of pyoverdine. 55Fe uptake assays demonstrated that both AA-Fe and DHA-Fe complexes are transported via FemA; however, no uptake was observed for PCH-Fe through this transporter. Structural studies revealed that FemA is able to bind AA2-Fe or DHA2-Fe complexes. Key interactions are conserved between FemA and these two complexes, with specificity primarily driven by one of the two siderophore molecules. Interestingly, although no iron uptake was noted for PCH through FemA, the transporter also binds PCH-Fe in a similar manner. These findings show that under moderate iron deficiency, when only PCH is produced by P. aeruginosa, degradation products AA and DHA enhance iron uptake by inducing femA expression and facilitating iron transport through FemA. This provides new insights into the pathogen's strategies for iron homeostasis.

Plants, Microorganisms and Their Metabolites in Supporting Asbestos Detoxification-A Biological Perspective in Asbestos Treatment

Many countries banned asbestos due to its toxicity, but considering its colossal use, especially in the 1960s and 1970s, disposing of waste containing asbestos is the current problem. Today, many asbestos disposal technologies are known, but they usually involve colossal investment and operating expenses, and the end- and by-products of these methods negatively impact the environment. This paper identifies a unique modern direction in detoxifying asbestos minerals, which involves using microorganisms and plants and their metabolites. The work comprehensively focuses on the interactions between asbestos and plants, bacteria and fungi, including lichens and, for the first time, yeast. Biological treatment is a prospect for in situ land reclamation and under industrial conditions, which can be a viable alternative to landfilling and an environmentally friendly substitute or supplement to thermal, mechanical, and chemical methods, often characterized by high cost intensity. Plant and microbial metabolism products are part of the green chemistry trend, a central strategic pillar of global industrial and environmental development.

The diversity and utility of arylthiazoline and aryloxazoline siderophores: challenges of total synthesis

Siderophores are unique ferric ion chelators produced and secreted by some organisms like bacteria, fungi and plants under iron deficiency conditions. These molecules possess immense affinity and specificity for Fe³⁺ and other metal ions, which attracts great interest due to the numerous possibilities of application, including antibiotics delivery to resistant bacteria strains. Total synthesis of siderophores is a must since the compounds are present in natural sources at extremely small concentrations. These molecules are extremely diverse in terms of molecular structure and physical and chemical properties. This review is focused on achievements and developments in the total synthesis strategies of naturally occurring siderophores bearing arylthiazoline and aryloxazoline units.

A review presents advances in total synthesis of thiazoline and oxazoline-bearing siderophores, unique ferric ion chelators found in some bacteria, fungi and plants.

Siderophore-mediated zinc acquisition enhances enterobacterial colonization of the inflamed gut

Zinc is an essential cofactor for bacterial metabolism, and many Enterobacteriaceae express the zinc transporters ZnuABC and ZupT to acquire this metal in the host. However, the probiotic bacterium Escherichia coli Nissle 1917 (or "Nissle") exhibits appreciable growth in zinc-limited media even when these transporters are deleted. Here, we show that Nissle utilizes the siderophore yersiniabactin as a zincophore, enabling Nissle to grow in zinc-limited media, to tolerate calprotectin-mediated zinc sequestration, and to thrive in the inflamed gut. We also show that yersiniabactin's affinity for iron or zinc changes in a pH-dependent manner, with increased relative zinc binding as the pH increases. Thus, our results indicate that siderophore metal affinity can be influenced by the local environment and reveal a mechanism of zinc acquisition available to commensal and pathogenic Enterobacteriaceae.

Elucidation of crude siderophore extracts from supernatants of Pseudomonas sp. ZnCd2003 cultivated in nutrient broth supplemented with Zn, Cd, and Zn plus Cd

This research aimed to study siderophores secreted from Pseudomonas sp. PDMZnCd2003, a Zn/Cd tolerant bacterium. The effects of Zn and/or Cd stress were examined in nutrient broth to achieve the actual environmental conditions. Acid and alkali supernatants and liquid-liquid extraction with ethyl acetate and butanol were carried out to obtain crude extracts containing different amounts of the metals. The bacterial growth, UV-visible spectra of the supernatants and siderophore production indicated that the production of siderophores tended to be linked to primary metabolites. Pyocyanin was produced in all treatments, while pyoverdine was induced by stress from the metals, especially Cd. FT-IR spectra showed C=O groups and sulfur functional groups that were involved in binding with the metals. LC-MS revealed that pyocyanin, 1-hydroxy phenazine, pyoverdine, and pyochelin were present in the crude extracts. S K-edge XANES spectra showed that the main sulfur species in the extracts were the reduced forms of sulfide, thiol, and disulfide, and their oxidation states were affected by coordination with Zn and/or Cd. In addition, Zn K-edge EXAFS spectra and Cd K-edge EXAFS spectra presented Zn-O and Cd-O as coordination in the first shell, in case the extracts contained less metal. Although the mix O/S ligands had chelation bonding with Zn and Cd in the other extracts. For the role of S groups in pyochelin binding with the metals, this was the first report. The results of these experiments could be extended to Pseudomonas that respond to metal contaminated environments.

Iron acquisition with the natural siderophore enantiomers pyochelin and enantio-pyochelin in Pseudomonas species

The bacterial siderophore pyochelin is composed of salicylate and two cysteine-derived heterocycles, the second of which is modified by reduction and N-methylation during biosynthesis. 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. Stereochemistry is opposite in the Pseudomonas fluorescens siderophore enantio-pyochelin, in which the first ring originates from L-cysteine and the second ring from D-cysteine. Both siderophores promote growth of the producer organism during iron limitation and induce the expression of their biosynthesis genes by activating the transcriptional AraC-type regulator PchR. However, neither siderophore is functional as an iron carrier or as a transcriptional inducer in the other species, demonstrating that both processes are highly stereospecific. Stereospecificity of pyochelin/enantio-pyochelin-mediated iron uptake is ensured at two levels: (i) by the outer membrane siderophore receptors and (ii) by the cytosolic PchR regulators.

A review of recent trends in electrospray ionisation-mass spectrometry for the analysis of metal-organic ligand complexes

Electrospray ionisation-mass spectrometry (ESI-MS) is used in a wide variety of fields to examine the formation, stoichiometry and speciation of complexes involving metals and organic ligands. This article reviews the literature in this area over the past 5 years, examining trends in ESI-MS use and novel applications that enhance the scope of the technique. ESI-MS can provide direct information on changes in speciation with metal:ligand ratio and pH, identify metal oxidation state directly and allow insight into competitive interactions in ternary systems. However, both the instrumental set-up and artefacts in the electrospraying process can affect the species distribution observed, and changes in solution chemistry can affect the relative ion intensity of species. Therefore, ESI-MS data is at its most powerful when corroborated by data from other experimental techniques, such as pH potentiometry. The challenges in interpreting direct ESI-MS data quantitatively are discussed in detail, with reference to differences in the ion intensities of species, signal suppression and quantifying species distributions. The use of HPLC-ESI-MS is also reviewed, highlighting challenges and applications. Overall, the need for more standard reporting of quality assurance data is discussed, to strengthen the applications of ESI-MS to metal-organic ligand complexes further.

Infrared multiphoton dissociation of the siderophore enterobactin and its Fe(III) complex. Influence of Fe(III) binding on dissociation kinetics and relative energetics

The dissociation pathways of the siderophore enterobactin and its complex with Fe(III) were examined using infrared multiphoton dissociation (IRMPD). Under experimental conditions (pH = 3.5), both compounds' electrospray spectra exhibited exclusively singly-charged anions. The compositions of the dissociation products were characterized by accurate mass measurements using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The primary dissociation channel for both species was determined to be the loss of one serine group from the precursor molecules. To further investigate the influence of Fe(III) binding on the intramolecular interactions, dissociation kinetics and relative energetics for the loss of this serine group were determined using the focused radiation for gaseous multiphoton energy-transfer (FRAGMENT) method. From the kinetic data, it was found that enterobactin was approximately seven times more reactive than its Fe(III) complex over the range of laser intensities investigated. The relative activation energies, however, exhibited similar values, approximately 7 kcal.mol(-1). These results suggest that at pH = 3.5, Fe(III) interacts with only two of the three serine groups. The results from the present work are believed to be valuable for the characterization of novel siderophores as well as their associated metabolites and synthetic analogues.