Role of Siderophores in Bio-Control
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Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+
Pathogen
Siderophores
Antagonist
Role of Siderophores in Bio-control
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Mechanism of Action:
Competition-for nutrients, i.e. Iron
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Siderophores
• Are the extra cellular, low molecular weight(500 to 1000 Daltons), virtually Fe III (ferric)-specific legands produced as scavenging agent in order to combat low iron stress.
• Iron chelating agents (Proteins)- make complex with iron III with high affinity.
Most aerobic and facultative anaerobic microorganisms respond to low iron stress by producing siderophores.
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On the basis of their chemical
structure: • Two distinct type;
• Catecholate type: with catechol residue
• Hydroxymate type: with hydroxymic acid residue
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Other general charecteristics:• They are also produced by some plants-
phytosiderophores• Produced by one organism can be utilized by
another organism although there is great deal of specificity in their uptake mechanism.
• Are utilized specifically i.e, the producer organisms have special receptors for their utilization.
• Condition of low iron solubility in soil, iron chelators are extremely important for mobilizing iron and increasing its availability to plant and microbes.
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• Operate in Gram-negative and Gram-positive bacterial spp,
• Animal and plant pathogens,
• Aerobic bacteria and fungi,
• Symbiotic and free living nitrogen fixing bacteria and others.
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Microorganism Siderophores
A. Fungi
Aspergillus spp. &Penicillium spp.
Ferrichromes
Neurospora spp & Ustilago spp.
Copnogen
Rhodotorula sp. Rhodotorulic acid
Ectomycorrhizal spp. Hydroxymate type
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B. Bacteria
Actinomyces sp. Ferrioxamines
Agrobacterium tumefaciens
Agrobactin
Anabaena sp. Schizokinen
Arthrobacter sp. Arthrobactin
Bacillus megaterium Schizokinen
Enteric sp. Agrobactin, Enterobactin
Pseudomonas sp. Pseudobactin,Pyochelin, Pyoverdine,Terribactin
Mycobacteria Mycobactins
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Sidrophore produced by bacterial antagonists-Glimpses of Plant Pathology-TNAU-V.Sendhilvel,…
• Siderophore1) Schizokien2) Azotobactin3) Pseudobactin4) Rhizobactin5) Anguibactin6) Pyoverdin7) Cepabactin8) Chrysobactin9) Staphyloferrin A10)Ferribactin11)Ornibactin12)Desferrioxamine B&E
• Producing organism1) Bacillus megaterium,Ralstonia
solancearum2) Azotobacter vinelandii3) Pseudomonas putida B 104) Rhizobium meliloti5) Vibriotanguillarum 775 (PJM)6) Pseudomonas aeruginosa,
P.chlororaphis,7) P.cepacia8) Erwinia chrysanthemi9) Staphylococcus hyicus10)Pseudomonas fluorescens11)Pseudomonas cepacia12)Streptomyces viridosporus
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Examples of siderophores produced by various
bacteria and fungi are: Wikipedia
• ferrichrome (Ustilago sphaerogena),• enterobactin (Escherichia coli), • enterobactin and bacillibactin (Bacillus subtilis),• ferrioxamine B (Streptomyces pilosus),• fusarinine C (Fusarium roseum), • yersiniabactin (Yersinia pestis),• vibriobactin (Vibrio cholerae),• azotobactin (Azotobacter vinelandii), • pseudobactin (Pseudomonas B 10) • or erythrobactin (Saccharopolyspora erythraea
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• Rhizobaceria, Pseudomonas fluorescens,P.putida:
-- fluorescent,yellow-green water soluble siderophores with both hydroxymate and phenolate groups.
Classified as either pyoviridins or pseudobactins.
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• Different siderophores differ in their affinity for iron and other cations-competition between siderophores .
• If an antagonist produces a better siderophores than the pathogen, then the pathogen could be deprived of iron and therefore grows less well.
• Kloepper et al (1980) were the first to demonstrate the importance of siderophores in bio-control.
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• Role of bacterial siderophores in dissolution of hornblende-L.J.Liermann et al.
• Fe(III) is unavailableto cells in aerobic environments due to low solubility of Fe oxyhydroxides near neutral pH.
• Siderophores(Gk.=iron bearer) denotes a virtually Fe(III)-specific ligand that produced by aerobic bacteria and fungi growing under low iron conditions.
• Most are of either the hydroxamate (eg.ferrioxamines) or catechol class; others include carboxylates and pyoverdines.
• Those with hexadentate coordination of Fe(III) have higher affinity than those with tetradentate or bidentate coordination.
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• The siderophore released by Streptomyces sp. was identified as a catecholamide, which is unusual for Streptomycetes.
• However, there are known mixed ligand siderophores produced by actinomycetes (Catechol-hydroxamate).
• The hydroxamates are generated by the microorganism in a higher iron environment, whereas the catecholamide works as a “ back-up” system when the iron concentrations are lower.
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• Role of iron in rhizobacteria-mediated induced systemic resistance of cucumber-C.M.Press et al.
• Seed treatment with the rhizosphere bacterium Serratia marcescens strain 90-166 suppressed anthracnose of cucumber, caused by Colletotrichum orbiculare, through ISR.
• When the iron concentration of a planting mix was decreased by addition of an iron chelator, suppression of anthracnose by strain 90-166 was significantly improved. The strain produced 465+/-70 mg/litre of catechol siderophore.
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• ISR induced by Pseudomonas fluorescens wcs374 against Fusarium wilt of radish is inversely related to iron availability of the planting substrate.
• Among siderophores produced by rhizosphere bacteria, only the pyoverdines (also called pseudobactins) produced by the fluorescent pseudomonads have been implicated in ISR.
• The siderophore produced by 90-166 has not been identified, but other strains of Serratia marcescens produce the catechol siderophore enterobactin.
• Pyoverdin deficient strain of P.fluorescens CHAO(CHA400) no longer induced resistance against Tobacco necrosis virus in tobacco.
• Siderophores differ in their influence on plant resistance responses or that some bacterial strains have additional characteristics inolved in ISR that can compensate for lack of siderophore production.
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• Antifungals from fluorescent pseudomonads: biosynthesis and regulation-Deepti
Dwivedi&B.N.Johri.
• Pseudomonads can indirectly suppress fungal pathogens by scavenging iron in the rhizosphere environment through the release of siderophores (Pyoverdins).
• Under Fe-starvation conditions, siderophores can trap traces of insoluble complexes. Such complexes are internalized into cells through specific membrane-bound receptors.
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• Isolation of siderophore-producing strains of Rhizobium meliloti and their biocontrol potential against macrophomina phaseolina that causes charcoal rot
of groundnut-N.K.Arora,S.C.kang&D.K.Maheshwari.
• Use of antagonistic rhizobia has an added advantage in that they have also the ability to fix nitrogen. Different strain of rhizobia have now been reported to produce siderophores (Catechol-phenolic type and hydroxamate type)
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• Book:• Siderophore may also act as growth factor• Some are potent antibiotic exhibiting both
fungicidal and bactericidal effects under low iron.
• Various compounds of siderophores produced by fluorescent pseudomonads are: ferrichrome, ferrioxamine, phytosiderophores, pseudobactin B10, pyochelin, pyoverdine,etc.
• In phyllosphere, siderophores may originate from the plant (Phytosiderophores) or from colonizing microorganisms.
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• Phytosiderophores, found only in some grasses are produced under iron-limiting conditions.
• These are mugieneic acid from barley,
• Avenic acid-A from oat and
• 2-deoxymugineic acid from wheat
• Phytosiderophores appear to have less affinity than microbial siderophores for ferric ion.
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