From a total synthesis of cepabactin and its 3:1 ferric complex to the isolation of a 1:1:1 mixed complex between iron (III), cepabactin and pyochelin

A novel and straightforward total synthesis of cepabactin and its iron (III) complex is described. The latter compound was compared and identified to that obtained from the cultures of Burkholderia cepacia. On treatment of the growth medium of two different strains of B. cepacia with ferric chloride, we have isolated and characterized an unexpected mixed complex of iron (III), cepabactin and pyochelin.     

Binding properties of pyochelin and structurally related molecules to FptA of Pseudomonas aeruginosa

Pyochelin (Pch) is a siderophore that is produced in iron-limited conditions, by both Pseudomonas aeruginosa and Burkholderia cepacia. This iron uptake pathway could therefore be a target for the development of new antibiotics. Pch is (4'R,2'R/S,4'R)-2'-(2-hydroxyphenyl)-3'-methyl-4',5',2',3',4',5'-hexahydro-[4',2']bithiazolyl-4'-carboxylic acid, and has three chiral centres located at positions C4', C2' and C4'. In P.aeruginosa, this siderophore chelates iron in the extracellular medium and transports it into the cells via a specific outer membrane transporter FptA. Docking experiments using the X-ray structure of FptA-Pch-Fe showed that iron-loaded or unloaded Pch diastereoisomers could bind to FptA. This was confirmed by in vivo binding assays. These binding properties and the iron uptake ability were not affected by removal of the C4' chiral centre. After removal of both the C4' and C2' chiral centres, the molecule still bound to FptA but was unable to transport iron. The overall binding mode of this iron-complexed analogue was inverted. These findings describe the first antagonist of the Pch/FptA iron uptake pathway. Pch also complexes with iron in conjunction with other bidentate ligands such as cepabactin (Cep) or ethylene glycol. Docking experiments showed that such complexes bind to FptA via the Pch molecule. The mixed Pch-Fe-Cep complex was also recognized by FptA, having an affinity intermediate between that for Pch(2)-Fe and Cep(3)-Fe. Finally, the iron uptake properties of the different Pch-related molecules suggested a mechanism for FptA-Pch-Fe complex formation similar to that of the FpvA/Pvd uptake system. All these findings improve our understanding of specificity of the interaction between FptA and its siderophore.     

Iron metabolism in Pseudomonas: salicylic acid, a siderophore of Pseudomonas fluorescens CHAO.

Under iron-starvation conditions of growth, Pseudomonas fluorescens CHA0, a soil isolate involved in phytopathogenic fungi antagonisms, produced, together with pyoverdine, a second iron-chelating compound which was purified and identified by spectroscopy, HPLC and 1H-NMR to be salicylic acid. Mutants unable to synthesize pyoverdine overproduced this compound by a factor of 9-14. The biosynthesis of salicylic acid was under iron control; it was fully inhibited by 5 microM added iron in the growth medium. In contrast, salicylic acid of either bacterial or commercial origin facilitated labeled iron incorporation in iron-starved cells. Based on these two relationships observed with bacterial iron metabolism it is concluded that salicylic acid has a siderophore function for this strain.     

Metabolic utilization of 57Fe-labeled coprogen in Neurospora crassa. An in vivo M?ssbauer study

M?ssbauer spectra of whole cells of Neurospora crassa arg-5 ota aga (a siderophore-free mutant) show that the siderophore coprogen is accumulated inside the cell as an entity. 57Fe from 57Fe-labeled coprogen is slowly removed from the complex (45% in 27 h). The rate of removal depends on the degree of iron starvation of the cells. The distribution of 55Fe from [55Fe]coprogen in vacuoles, membranes, and cytoplasm has been also determined. From this it is clear that coprogen is accumulated in the cytoplasm. In addition to its role as a siderophore, coprogen serves as an iron-storage compound. No holoferritins could be detected. We therefore conclude that this type of iron-storage protein is lacking in N. crassa. Metabolized iron was found predominantly to exist as an envelope of Fe(II) high-spin (delta = 1.2-1.3 mm s-1; delta EQ = 3.0-3.1 mm s-1 at 4.2 K) and fast-relaxing Fe(III) high-spin species (delta approximately equal to 0.25 mm s-1 and 0.45 mm s-1; delta EQ approximately equal to 0.6 mm s-1 and 0.55 mm s-1, respectively, at 4.2 K). An assignment of these major iron metabolites is difficult. The M?ssbauer data of the Fe(II) species do not fit those reported for heme, cytochromes and ferredoxins. We therefore assume that this iron metabolite represents a novel internal iron compound. One of the Fe(III) species becomes the dominant component of the cell spectra after 65 h of metabolization and might correspond to an iron-storage compound with iron oxide cores similar to bacterioferritin. After 27 h of growth in mycelia supplied with 57Fe-labeled coprogen, the siderophore ferricrocin was observed in the cell spectra. This is unexpected, since N. crassa arg-5 ota aga is unable to synthesize ornithine. We assume that ferricrocin is synthesized by the use of coprogen degradation products.     

Antimicrobial effects of novel siderophores linked to beta-lactam antibiotics

As a strategy to increase the penetration of antibiotic drugs through the outer membrane of gram-negative pathogens, facilitated transport through siderophore receptors has been frequently exploited. Hydroxamic acids, catechols, or very close isosteres of catechols, which are mimics of naturally occurring siderophores, have been used successfully as covalently linked escorting moieties, but a much wider diversity of iron binding motifs exists. This observation, coupled to the relative lack of specificity of siderophore receptors, prompted us to initiate a program to identify novel, noncatechol siderophoric structures. We screened over 300 compounds for their ability to (1) support growth in low iron medium of a Pseudomonas aeruginosa siderophore biosynthesis deletion mutant, or (2) compete with a bactericidal siderophore-antibiotic conjugate for siderophore receptor access. From these assays we identified a set of small molecules that fulfilled one or both of these criteria. We then synthesized these compounds with functional groups suitable for attachment to both monobactam and cephalosporin core structures. Siderophore-beta-lactam conjugates then were tested against a panel of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains. Although several of the resultant chimeric compounds had antimicrobial activity approaching that of ceftazidime, and most compounds demonstrated very potent activity against their cellular targets, only a single compound was obtained that had enhanced, siderophore-mediated antibacterial activity. Results with tonB mutants frequently showed increased rather than decreased susceptibilities. suggesting that multiple factors influenced the intracellular concentration of the drugs.     

Effects of growth rate and nutrient limitation on virulence factor production in Burkholderia cepacia.

The influence of growth rate and oxygen availability on siderophore, protease, and lipase production in Burkholderia cepacia was assessed for cells grown in a chemostat under iron limitation. Whereas siderophore and protease production increased with growth rate and oxygen yet decreased under oxygen depletion, lipase production demonstrated the opposite trend.     

Crystal structure at high resolution of ferric-pyochelin and its membrane receptor FptA from Pseudomonas aeruginosa

Pyochelin is a siderophore and virulence factor common to Burkholderia cepacia and several Pseudomonas strains. We describe at 2.0 A resolution the crystal structure of the pyochelin outer membrane receptor FptA bound to the iron-pyochelin isolated from Pseudomonas aeruginosa. One pyochelin molecule bound to iron is found in the protein structure, providing the first three-dimensional structure at the atomic level of this siderophore. The pyochelin molecule provides a tetra-dentate coordination of iron, while the remaining bi-dentate coordination is ensured by another molecule not specifically recognized by the protein. The overall structure of the pyochelin receptor is typical of the TonB-dependent transporter superfamily, which uses the proton motive force from the cytoplasmic membrane through the TonB-ExbB-ExbD energy transducing complex to transport ferric ions across the bacterial outer membrane: a transmembrane 22 beta-stranded barrel occluded by a N-terminal domain that contains a mixed four-stranded beta-sheet. The N-terminal TonB box is disordered in two crystal forms, and loop L8 is found to point towards the iron-pyochelin complex, suggesting that the receptor is in a transport-competent conformation.     

Iron transport-mediated antagonism between plant growth-promoting and plant-deleterious Pseudomonas strains

Both plant growth-promoting Pseudomonas B10 and its yellow-green, fluorescent iron transport agent (siderophore) pseudobactin enhance potato growth and biologically control certain soil-borne fungal diseases in part by depriving specific root-colonizing endemic microorganisms including phytopathogens of iron(III), thus inhibiting their growth. The present study examines this mode of iron deprivation. The growth inhibition of certain bean-deleterious fluorescent pseudomonads by specific bean-beneficial fluorescent pseudomonads is due in part to the inability of susceptible strains to utilize siderophores from beneficial strains to transport iron(III). Conversely, deleterious strains which were able to utilize siderophores from beneficial strains were not inhibited. The ability of a given pseudomonad to utilize another pseudomonad's siderophore may depend upon its possessing a specific outer membrane receptor protein for that pseudomonad's ferric siderophore. Siderophore-mediated competition for iron in microbial systems appears to be a widespread phenomenon.     

Ornibactin production and transport properties in strains of Burkholderia vietnamiensis and Burkholderia cepacia (formerly Pseudomonas cepacia)

Several strains of Burkholderia vietnamiensis, isolated from the rhizosphere of rice plants, and four strains formerly known as Pseudomonas cepacia including two collection strains and two clinical isolates were compared for siderophore production and iron uptake. The B. vietnamiensis (TVV strains) as well as the B. cepacia strains (ATCC 25416 and ATCC 17759) and the clinical isolates K132 and LMG 6999 were all found to produce ornibactins under iron starvation. The two ATCC strains of B. cepacia additionally produced the previously described siderophores, pyochelin and cepabactin. Analysis of the ratio of isolated ornibactins (C4, C6 and C8) by HPLC revealed nearly identical profiles. Supplementation of the production medium with ornithine (20 mm) resulted in a 2.5-fold increase in ornibactin synthesis. Ornibactin-mediated iron uptake was independent of the length of the acyl side chain and was observed with all strains of B. vietnamiensis and B. cepacia, but was absent with strains of Pseudomonas aeruginosa, Pseudomonas fluorescens and Pseudomonas stutzeri, known to produce pyoverdines or desferriferrioxamines as siderophores. These results suggest that ornibactin production is a common feature of all Burkholderia strains and that these strains develop an ornibactin-specific iron transport system which is distinct from the pyoverdine-specific transport in Pseudomonas strains.     

A siderophore from Pseudomonas putida type A1: structural and biological characterization

A siderophore from a root-colonizing, plant-beneficial fluorescent Pseudomonas (P. putida type A1) isolated from chickpea rhizosphere was studied. Culture conditions required for optimal production of the chromophore by the organism were standardized. The compound was purified by gel filtration, ion exchange and RP-HPLC chromatographic procedures. The purified compound exhibited siderophore activity for P. putida and antifungal activity on phytopathogens, Fusarium oxysporum f. sp. ciceri and Helminthosporium oryzae. Growth inhibition of the pathogens was observed under iron-deficient conditions. Complete acid hydrolysis of the compound revealed that it is a peptide containing Asx, Thr, Glx, Val, His, Lys, Ser and Gly. Spectral analysis revealed that it contains hydroxyquinoline-based chromophore in addition to an aromatic residue and the molecular weight of the compound was 1.5 kDa. EPR analysis of the peptide-chromophore-iron complex showed that the compound binds to iron and the bound iron was in the Fe(3+) oxidation state having a high spin d(5) system. The peptide-chromophore-iron complex takes a turn structure in solution as shown by circular dichroism spectroscopy, a feature which was hitherto not known for other siderophores. The siderophore studied here is unique in this respect but otherwise strikingly similar to other pseudobactin-type siderophores of plant growth-promoting and plant-deleterious pseudomonads. The possible functional significance of the compound is discussed in relation to the secondary structure described earlier for siderophores.     

Burkholderia cepacia XXVI siderophore with biocontrol capacity against Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is the causal agent of anthracnose in mango. Burkholderia cepacia XXVI, isolated from mango rhizosphere and identified by 16S rDNA sequencing as a member of B. cepacia complex, was more effective than 6 other mango rhizosphere bacteria in inhibiting the model mango pathogen, C. gloeosporioides ATCC MYA 456. Biocontrol of this pathogen was demonstrated on Petri-dishes containing PDA by > 90 % reduction of surface colonization. The nature of the biocontrol metabolite(s) was characterized via a variety of tests. The inhibition was almost exclusively due to production of agar-diffusible, not volatile, metabolite(s). The diffusible metabolite(s) underwent thermal degradation at 70 and 121 °C (1 atm). Tests for indole acetic acid production and lytic enzyme activities (cellulase, glucanase and chitinase) by B. cepacia XXVI were negative, indicating that these metabolites were not involved in the biocontrol effect. Based on halo formation and growth inhibition of the pathogen on the diagnostic medium, CAS-agar, as well as colorimetric tests we surmised that strain XXVI produced a hydroxamate siderophore involved in the biocontrol effect observed. The minimal inhibitory concentration test showed that 0.64 μg ml(-1) of siderophore (Deferoxamine mesylate salt-equivalent) was sufficient to achieve 91.1 % inhibition of the pathogen growth on Petri-dishes containing PDA. The biocontrol capacity against C. gloeosporioides ATCC MYA 456 correlated directly with the siderophore production by B. cepacia XXVI: the highest concentration of siderophore production in PDB on day 7, 1.7 μg ml(-1) (Deferoxamine mesylate salt-equivalent), promoted a pathogen growth inhibition of 94.9 %. The growth of 5 additional strains of C. gloeosporioides (isolated from mango "Ataulfo" orchards located in the municipality of Chahuites, State of Oaxaca in Mexico) was also inhibited when confronted with B. cepacia XXVI. Results indicate that B. cepacia XXVI or its siderophore have the potential to be used as a biological control agent against C. gloeosporioides; thus diminishing environmental problems caused by the current practices to control this disease.     

The Pseudomonas aeruginosa pirA gene encodes a second receptor for ferrienterobactin and synthetic catecholate analogues

Actively secreted iron chelating agents termed siderophores play an important role in the virulence and rhizosphere competence of fluorescent pseudomonads, including Pseudomonas aeruginosa which secretes a high affinity siderophore, pyoverdine, and the low affinity siderophore, pyochelin. Uptake of the iron-siderophore complexes is an active process that requires specific outer membrane located receptors, which are dependent of the inner membrane-associated protein TonB and two other inner membrane proteins, ExbB and ExbC. P. aeruginosa is also capable of using a remarkable variety of heterologous siderophores as sources of iron, apparently by expressing their cognate receptors. Illustrative of this feature are the 32 (of which 28 putative) siderophore receptor genes observed in the P. aeruginosa PAO1 genome. However, except for a few (pyoverdine, pyochelin, enterobactin), the vast majority of P. aeruginosa siderophore receptor genes still remain to be characterized. Ten synthetic iron chelators of catecholate type stimulated growth of a pyoverdine/pyochelin deficient P. aeruginosa PAO1 mutant under condition of severe iron limitation. Null mutants of the 32 putative TonB-dependent siderophore receptor encoding genes engineered in the same genetic background were screened for obvious deficiencies in uptake of the synthetic siderophores, but none showed decreased growth stimulation in the presence of the different siderophores. However, a double knock-out mutant of ferrienterobactin receptor encoding gene pfeA (PA 2688) and pirA (PA0931) failed to be stimulated by 4 of the tested synthetic catecholate siderophores whose chemical structures resemble enterobactin. Ferric-enterobactin also failed to stimulate growth of the double pfeA-pirA mutant although, like its synthetic analogues, it stimulated growth of the corresponding single mutants. Hence, we confirmed that pirA represents a second P. aeruginosa ferric-enterobactin receptor. The example of these two enterobactin receptors probably illustrates a more general phenomenon of siderophore receptor redundancy in P. aeruginosa.     

The metal dependence of pyoverdine interactions with its outer membrane receptor FpvA

To acquire iron, Pseudomonas aeruginosa secretes the fluorescent siderophore pyoverdine (Pvd), which chelates iron and shuttles it into the cells via the specific outer membrane transporter FpvA. We studied the role of iron and other metals in the binding and transport of Pvd by FpvA and conclude that there is no significant affinity between FpvA and metal-free Pvd. We found that the fluorescent in vivo complex of iron-free FpvA-Pvd is in fact a complex with aluminum (FpvA-Pvd-Al) formed from trace aluminum in the growth medium. When Pseudomonas aeruginosa was cultured in a medium that had been treated with a metal affinity resin, the in vivo formation of the FpvA-Pvd complex and the recycling of Pvd on FpvA were nearly abolished. The accumulation of Pvd in the periplasm of Pseudomonas aeruginosa was also reduced in the treated growth medium, while the addition of 1 microM AlCl(3) to the treated medium restored the effects of trace metals observed in standard growth medium. Using fluorescent resonance energy transfer and surface plasmon resonance techniques, the in vitro interactions between Pvd and detergent-solubilized FpvA were also shown to be metal dependent. We demonstrated that FpvA binds Pvd-Fe but not Pvd and that Pvd did not compete with Pvd-Fe for FpvA binding. In light of our finding that the Pvd-Al complex is transported across the outer membrane of Pseudomonas aeruginosa, a model for siderophore recognition based on a metal-induced conformation followed by redox selectivity for iron is discussed.     

Degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS

A bacterium was isolated from water by enrichment on 2-chlorobenzoate as sole source of carbon and energy. Based on morphological and physiological properties, this microorganism was assigned to the species Pseudomonas cepacia. The organism was designated Pseudomonas cepacia 2CBS. During growth on 2-chlorobenzoate, the chlorine substituent was released quantitatively, and a small amount of 2,3-dihydroxybenzoate accumulated in the culture medium. Mutants of Pseudomonas cepacia 2CBS were induced by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Some of these mutants produced catechol from 2-chlorobenzoate. Other mutants accumulated the meta-cleavage product of catechol, 2-hydroxy-cis,cis-muconic acid semialdehyde. In crude cell-free extracts of Pseudomonas cepacia 2CBS, an enzyme was detected which catalysed the conversion of 2-chlorobenzoate to catechol. Molecular oxygen, NADH and exogenous Fe2+ were required for activity. Stoichiometric amounts of chloride were released. Experiments with 18O2 revealed that both oxygen atoms in the hydroxyl groups of the product were derived from molecular oxygen. Thus, the enzyme catalysing the conversion of 2-chlorobenzoate was identified as 2-chlorobenzoate 1,2-dioxygenase (1,2-hydroxylating, dehalogenating, decarboxylating). 2-Chlorobenzoate 1,2-dioxygenase from Pseudomonas cepacia 2CBS was shown to be a multicomponent enzyme system. The activities of catechol 2,3-dioxygenase and catechol 1,2-dioxygenase were detected in crude cell-free extracts. The activity of catechol 2,3-dioxygenase was 60 times higher than the activity of catechol 1,2-dioxygenase, indicating that catechol is mainly degraded via meta-cleavage in Pseudomonas cepacia 2CBS. No enzyme was found which converted 2,3-dihydroxybenzoate, suggesting that this compound is a dead-end metabolite of 2-chlorobenzoate catabolism. A pathway for the degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS is proposed.     

Thioquinolobactin, a Pseudomonas siderophore with antifungal and anti-Pythium activity

Under conditions of iron limitation Pseudomonas fluorescens ATCC 17400 produces two siderophores, pyoverdine, and a second siderophore quinolobactin, which itself results from the hydrolysis of the unstable molecule 8-hydroxy-4-methoxy-2-quinoline thiocarboxylic acid (thioquinolobactin). Pseudomonas fluorescens ATCC 17400 also displays a strong in vitro antagonism against the Oomycete Pythium, which is repressed by iron, suggesting the involvement of a siderophore(s). While a pyoverdine-negative mutant retains most of its antagonism, a thioquinolobactin-negative mutant only slowed-down Pythium growth, and a double pyoverdine-, thioquinolobactin-negative mutant, which does not produce any siderophore, totally lost its antagonism against Pythium. The siderophore thioquinolobactin could be purified and identified from spent medium and showed anti-Pythium activity, but it was quickly hydrolysed to quinolobactin, which we showed has no antimicrobial activity. Analysis of antagonism-affected transposon mutants revealed that genes involved in haem biosynthesis and sulfur assimilation are important for the production of thioquinolobactin and the expression of antagonism.     

Exogenous siderophore-mediated iron uptake in Pseudomonas aeruginosa: possible involvement of porin OprF in iron translocation.

In addition to the two siderophores pyoverdine and pyochelin synthesized by Pseudomonas aeruginosa ATCC 15692 (strain PAO1), several siderophores produced by other bacteria or fungi, namely cepabactin, salicylic acid, desferriferrichrysin, desferriferricrocin, desferriferrioxamine B, desferriferrioxamine E and coprogen, were able to promote iron uptake with variable efficiencies into this bacterium. For most of these siderophores, these results were consistent with the growth stimulation produced by the same compounds in a plate bioassay. Desferriferrichrome A, enterobactin and desferriferrirubin, however, did not promote iron uptake, although enterobactin and desferriferrirubin stimulated bacterial growth. These paradoxical data are discussed in view of siderophore-inducible iron uptake systems, as demonstrated recently for enterobactin. Among the strains tested, including the wild-type PAO1, the pyoverdine-less mutant PAO6606 and the two porin-mutants P. aeruginosa H636 (oprF::omega) and P. aeruginosa H673 (oprD::Tn501), only for the porin-OprF mutant were fewer siderophores able to promote iron uptake compared to the other strains. Such results suggest that beside specific routes for iron uptake P. aeruginosa is also able to take up siderophore-liganded iron through OprF.     

Burkholderia pseudomallei known siderophores and hemin uptake are dispensable for lethal murine melioidosis

Burkholderia pseudomallei is a mostly saprophytic bacterium, but can infect humans where it causes the difficult-to-manage disease melioidosis. Even with proper diagnosis and prompt therapeutic interventions mortality rates still range from >20% in Northern Australia to over 40% in Thailand. Surprisingly little is yet known about how B. pseudomallei infects, invades and survives within its hosts, and virtually nothing is known about the contribution of critical nutrients such as iron to the bacterium's pathogenesis. It was previously assumed that B. pseudomallei used iron-acquisition systems commonly found in other bacteria, for example siderophores. However, our previous discovery of a clinical isolate carrying a large chromosomal deletion missing the entire malleobactin gene cluster encoding the bacterium's major high-affinity siderophore while still being fully virulent in a murine melioidosis model suggested that other iron-acquisition systems might make contributions to virulence. Here, we deleted the major siderophore malleobactin (mba) and pyochelin (pch) gene clusters in strain 1710b and revealed a residual siderophore activity which was unrelated to other known Burkholderia siderophores such as cepabactin and cepaciachelin, and not due to increased secretion of chelators such as citrate. Deletion of the two hemin uptake loci, hmu and hem, showed that Hmu is required for utilization of hemin and hemoglobin and that Hem cannot complement a Hmu deficiency. Prolonged incubation of a hmu hem mutant in hemoglobin-containing minimal medium yielded variants able to utilize hemoglobin and hemin suggesting alternate pathways for utilization of these two host iron sources. Lactoferrin utilization was dependent on malleobactin, but not pyochelin synthesis and/or uptake. A mba pch hmu hem quadruple mutant could use ferritin as an iron source and upon intranasal infection was lethal in an acute murine melioidosis model. These data suggest that B. pseudomallei may employ a novel ferritin-iron acquisition pathway as a means to sustain in vivo growth.     

Pseudomonas fluorescens CHA0 produces enantio-pyochelin, the optical antipode of the Pseudomonas aeruginosa siderophore pyochelin

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 4'R, 2'R, 4'R (pyochelin I) and 4'R, 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.     

Isolation and partial characterization of catechol-type siderophore fromPseudomonas stutzeri RC 7

Pseudomonas stutzeri RC 7 grown under iron-deficient conditions produced catecholtype siderophore, which was identified to be arginine conjugate of 2,3-dihydroxy-benzoic acid. Hydroxamic acids were not detected. The concentration of siderophore in the culture supernatant was maximal after 24 h of growth. Addition of iron to the medium increased bacterial growth but repressed the production of siderophore.