Identification of a system for hydroxamate xenosiderophore-mediated iron transport in Burkholderia cenocepacia.

One of the mechanisms employed by the opportunistic pathogen Burkholderia cenocepacia to acquire the essential element iron is the production and release of two ferric iron chelating compounds (siderophores), ornibactin and pyochelin. Here we show that B. cenocepacia is also able to take advantage of a range of siderophores produced by other bacteria and fungi ('xenosiderophores') that chelate iron exclusively by means of hydroxamate groups. These include the tris-hydroxamate siderophores ferrioxamine B, ferrichrome, ferricrocin and triacetylfusarinine C, the bis-hydroxamates alcaligin and rhodotorulic acid, and the monohydroxamate siderophore cepabactin. We also show that of the 24 TonB-dependent transporters encoded by the B. cenocepacia genome, two (FhuA and FeuA) are involved in the uptake of hydroxamate xenosiderophores, with FhuA serving as the exclusive transporter of iron-loaded ferrioxamine B, triacetylfusarinine C, alcaligin and rhodotorulic acid, while both FhuA and FeuA are able to translocate ferrichrome-type siderophores across the outer membrane. Finally, we identified FhuB, a putative cytoplasmic membrane-anchored ferric-siderophore reductase, as being obligatory for utilization of all of the tested bis- and tris-hydroxamate xenosiderophores apart from alcaligin

Iron oxide dissolution and solubility in the presence of siderophores

Abstract.: Iron is an essential trace nutrient for most known organisms. The iron availability is limited by the solubility and the slow dissolution kinetics of iron-bearing mineral phases, particularly in pH neutral or alkaline environments such as carbonatic soils and ocean water. Bacteria, fungi, and plants have evolved iron acquisition systems to increase the bioavailability of iron in such environments. A particularly efficient iron acquisition system involves the solubilization of iron by siderophores. Siderophores are biogenic chelators with high affinity and specificity for iron complexation. This review focuses on the geochemical aspects of biological iron acquisition. The significance of iron-bearing minerals as nutrient source for siderophore-promoted iron acquisition has been confirmed in microbial culture studies. Due to the extraordinary thermodynamic stability of soluble siderophore-iron complexes, siderophores have a pronounced effect on the solubility of iron oxides over a wide pH range. Very small concentrations of free siderophores in solution have a large effect on the solution saturation state of iron oxides. This siderophore induced disequilibrium can drive dissolution mechanisms such as proton-promoted or ligand-promoted iron oxide dissolution. The adsorption of siderophores to oxide surfaces also induces a direct siderophore-promoted surface-controlled dissolution mechanism. The efficiency of siderophores for increasing the solubility and dissolution kinetics of iron oxides are compared to other natural and anthropogenic ligand

Complexes Formed in Solution Between Vanadium(IV)/(V) and the Cyclic Dihydroxamic Acid Putrebactin or Linear Suberodihydroxamic Acid

The ability of microbial siderophores to coordinate metal ions, particularly Fe(III), continues to generate interest in the poten-tial applications of these bioligands in the environment and medicine.13 Siderophores produced by terrestrial and marin

Octadentate zirconium(IV)-loaded macrocycles with varied stoichiometry assembled from hydroxamic acid monomers using metal-templated synthesis

Published: February 28, 2017The reaction between Zr(IV) and the forward endo-hydroxamic acid monomer 4-[(5-aminopentyl)(hydroxy)amino]-4-oxobutanoic acid (for-PBH) in a 1:4 stoichiometry in the presence of diphenylphosphoryl azide and triethylamine gave the octadentate Zr(IV)-loaded tetrameric hydroxamic acid macrocycle for-[Zr(DFOT₁)] ([M + H]⁺ calc 887.3, obs 887.2). In this metal-templated synthesis (MTS) approach, the coordination preferences of Zr(IV) directed the preorganization of four oxygen-rich bidentate for-PBH ligands about the metal ion prior to ring closure under peptide coupling conditions. The replacement of for-PBH with 5-[(5-aminopentyl) (hydroxy)amino]-5-oxopentanoic acid (for-PPH), which contained an additional methylene group in the dicarboxylic acid region of the monomer, gave the analogous Zr(IV)-loaded macrocycle for-[Zr(PPDFOT₁)] ([M + H]⁺ calc 943.4, obs 943.1). A second, well-resolved peak in the liquid chromatogram from the for-PPH MTS system also characterized as a species with [M + H]⁺ 943.3, and was identified as the octadentate complex between Zr(IV) and two dimeric tetradentate hydroxamic acid macrocycles for-[Zr(PPDFOT1D)₂]. Treatment of for-[Zr(PPDFOT₁)] or for-[Zr(PPDFOT1D)₂] with EDTA at pH 4.0 gave the respective hydroxamic acid macrocycles as free ligands: octadentate PPDFOT₁ or two equivalents of tetradentate PPDFOT1D (homobisucaberin, HBC). At pH values closer to physiological, EDTA treatment of for-[Zr(DFOT₁)], for-[Zr(PPDFOT₁)], or Zr(IV) complexes with related linear tri- or tetrameric hydroxamic acid ligands showed the macrocycles were more resistant to the release of Zr(IV), which has implications for the design of ligands optimized for the use of Zr(IV)-89 in positron emission tomography (PET) imaging of cancer.William Tieu, Tulip Lifa, Andrew Katsifis, and Rachel Cod

Identificación y caracterización de moléculas biológicas microbianas con aplicación como inhibidores de corrosión

En el presente trabajo se realizó un estudio sistemático teórico-experimental para la determinación de las características estructurales que deben reunir los sideróforos para ser usados como inhibidores de corrosión ecológicos; se demostró que el sideróforo ferrioxamina B controla eficientemente los problemas de corrosión que se presentan en ambientes ácidos característicos de la industria petrolera. La ferrioxamina B es un sideróforo base trihidroxamato que funciona como inhibidor de corrosión ecológico a una concentración mínima de 75 ppm, fue purificado por técnicas cromatográficas y caracterizada a través de técnicas espectroscópicas de IR, RMN 1 H, RMN 13 C. El productor de la ferroxiamina B fue Bacillus sp., el cual se aisló de una muestra de suelo alcalino proveniente del Lago de Texcoco y se identificó a través de técnicas de Biología Molecular. La eficiencia de inhibición a la corrosión de la ferrioxamina B fue determinada a través de técnicas gravimétricas que se utilizan a nivel mundial para evaluar el desempeño de inhibidores de corrosión que se aplican actualmente en la industria petrolera. Una posible explicación, a través de simulación molecular, de cómo la ferrioxamina B controla el problema de corrosión en superficies de óxido de hierro fue propuesta. Además se diseñaron nuevos prototipos de inhibidores de corrosión anfifílicos ecológicos sintéticos base ferrioxamina B, los cuales tendrían las características estructurales idóneas para funcionar eficientemente a nivel industrial en ambientes corrosivos característicos de la industria petrolera.In the present work a theoretical-experimental systematic study for the determination of the structural characteristics that siderophores must reunite to be used like ecological corrosion inhibitors was realized, we demonstrated that ferrioxamine B siderophore controls efficiently problems of corrosion that appear in acid atmospheres characteristic of the oil industry. Ferrioxamine B is a siderophore base trihydroxamate that works like ecological corrosion inhibitor to minim concentration of 75 ppm, it was purified by chromatographic techniques and characterized through spectroscopic techniques IR, NMR 1 H, NMR 13 C. The producer of the ferroxiamine B was Bacillus sp., which was isolate of an originating alkaline soil sample of the Lake of Texcoco and it was identified through techniques of Molecular Biology. The efficiency of inhibition to the corrosion of the ferrioxamine B was determined through gravimetric techniques that are used at world level to evaluate the corrosion inhibitor performance which are applied actually in the oil industry. A possible explanation, through molecular simulation, of how the ferrioxamine B controls corrosion problems in iron oxide surfaces was proposed. In addition, new synthetic ecological amphiphilic corrosion inhibitor prototypes were designed base ferrioxamine B, which would have suitable structural characteristics to work efficiently at level industrial in corrosive atmosphere characteristic of the oil industry

Synthesis of peptides with hydroxamic acid side chain appendages.

Chapter 1 detailed the synthesis method of hydroxamate peptides derivatives of pentapeptide Ac-PHSXX\\u27-N-NH2 by solid phase hydroxamate peptide synthesis method. The glutamic acid/aspartic acid side chain was modified to hydroxamic acid by on resin N-C coupling. The hydroxamate benzyl protecting group was removed during HF cleavage. In Chapter 2 a novel multiple hydroxamic acid peptide siderophore was prepared and the metal binding activity of these peptides was studied by ESI-MS and MS/MS. Siderophore peptide Ac-Gly1-Glu2(NHOH)-D-Pro3-Gly4-Glu5(NHOH)-D-Pro6-NH2 was found to have significant preference to Fe(III) over Zn(II) and Ni(II), while the natural peptide analogue Ac-Gly1-Glu2-D-Pro 3-Gly4-Glu5-D-Pro6-NH2 did not show any obvious preference in these metal ions. The study of these multi hydroxamate ligands metal coordination revealed that the C-terminal binding site (Glu5(NHOH)) has the stronger chelation capability than the N terminal (Glu2(NHOH)) metal binding site and the amide bonds between glutamic acid and proline were identified as the most fragile bonds by MS/MS study

Identification and characterisation of novel iron acquisition mechanisms in Sinorhizobium meliloti 2011 and Pseudomonas aeruginosa

All known microorganisms with the exception of lactobacilli display an absolute requirement for iron. Although iron is the fourth most abundant element on earth, it is rapidly oxidised at neutral pH forming insoluble hydroxides. To overcome this limitation, microorganisms have developed a plethora of mechanisms to acquire iron. Sinorhizobium meliloti 2011, the endosymbiont of Medicago sativa, produces one known siderophore, rhizobactin 1021. Due to the high demand for iron in the nodule, the iron acquisition mechanisms of S. meliloti 2011 have been subject to particular interest. Rhizobactin 1021 is structurally similar to aerobactin, which is produced by various pathogenic bacteria In E. coli, aerobactin is transported at the inner membrane via the fhu system. The jhu system of E. coli was found to be sufficient to allow the transport of rhizobactin 1021 accross the inner membrane. A fhuC mutant was found to be defective in the transport of rhizobactin 1021. A novel permease, RhtX, was identified in S. meliloti and found to be involved in rhizobactin 1021 transport. Heterologous expression of RhtX in an E. coli JhuC mutant restored rhizobactin 1021 utilisation, but not aerobactin utilisation. A homologue of RhtX was identified in the opportunistic human pathogen P. aeruginosa. Mutation of the gznQ,fptX, was found to result in a deficiency in pyochelin utilisation in P. aeruginosa. P. aeruginosa was found to be capable of utilising the xenosiderophores rhizobactin 1021, schizokinen and aerobactin. A receptor mediating the transport of these siderophores was identified and characterised. S. meliloti 2011 has also been found to be capable of acquiring iron from haem compounds, a characteristic generally found only amongst pathogens. A number of putative haem acquisition loci were identified in S. meliloti 2011 and were subject to analyses. The protein encoded by Smc02726 was identified as the receptor for haemin and haemoglobin under free living conditions

The Chemistry and Biology of Iron-Scavenging Natural Products from Pathogenic Acinetobacter baumannii

Multidrug resistant (MDR) Gram-negative bacteria represent a global health crisis. Traditional antibiotics create selective pressure and breed resistance, making our current drugs less and less effective. Targeting of bacterial virulence factors has gained interest as an alternative strategy to potentially circumvent this problem. Virulent Acinetobacter baumannii synthesize and secrete pre-acinetobactin, a small molecule metal chelator that scavenges life-sustaining iron and is critical for establishing infection. The work described herein sheds light on the unusual properties of a non-enzymatic isomerization from pre-acinetobactin to acinetobactin and proposes a siderophore-swapping mechanism by which A. baumannii expands its pH window for virulence. Knowledge from structure-activity studies of the natural siderophores was used to design a rigidified pre-acinetobactin analog with antibiotic activity. Oxidation of the phenolate-oxazoline (pre-acinetobactin) to a phenolate-oxazole (oxidized pre-acinetobactin) confers low-micromolar MIC90 under iron deficient conditions against a panel of clinical MDR A. baumannii isolates. This work helps to lay a foundation for developing antivirulence agents to combat disease and resistance

Characterizing the heme binding properties of the iron regulated surface determinant proteins of Staphylococcus aureus

Staphylococcus aureus infection is becoming a widespread threat in both hospitals and communities worldwide, resulting in substantial treatment costs and numerous patient deaths. Bacterial survival is largely dependant on the organism’s ability to scavenge iron from a host via specialized pathways. The recently identified cell walland membrane-associated Iron regulated surface determinant (Isd) proteins are one such pathway. They serve to transport iron-containing heme, from hemoglobin, from the environment into the bacterial cell for nourishment. To date very little is known about the heme binding properties of these proteins and the overall Isd heme scavenging mechanism. Through the use of UV-visible absorption and magnetic circular dichroism spectroscopies, mass spectrometry, and mutational analysis, the heme-binding properties of IsdA, IsdC, and IsdE have been characterized. Recombinant IsdA (rIsdA) was found to bind a single high-spin ferric heme, coordinated by tyrosine 166 of the IsdA near abc transporter (NEAT) domain. Recombinant IsdC (rIsdC) was purified bound primarily to protoporphyrin IX, with traces of high-spin ferric heme and an unidentified ligand of approximately 320 Da. Recombinant IsdE (rIsdE) was purified bound to two heme molecules and an unidentified ligand of approximately 320 Da. One heme is ferric and is bound near the edge of a heme binding pocket through the imidazole group of histidine 229. The other is low-spin ferrous and is inaccessible to small ligands. The ferrous heme binding amino acid residue(s) remain unknown but it appears to be bound deep within the heme binding pocket of rIsdE. ii