Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+ Fe3+

Pathogen

Siderophores

Antagonist

Role of Siderophores in Bio-control

Mechanism of Action:

Competition-for nutrients, i.e. Iron

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.

On the basis of their chemical

structure: • Two distinct type;

• Catecholate type: with catechol residue

• Hydroxymate type: with hydroxymic acid residue

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.

• 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.

Microorganism Siderophores

A. Fungi

Aspergillus spp. &Penicillium spp.

Ferrichromes

Neurospora spp & Ustilago spp.

Copnogen

Rhodotorula sp. Rhodotorulic acid

Ectomycorrhizal spp. Hydroxymate type

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

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

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

• Rhizobaceria, Pseudomonas fluorescens,P.putida:

-- fluorescent,yellow-green water soluble siderophores with both hydroxymate and phenolate groups.

Classified as either pyoviridins or pseudobactins.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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)

• 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.

• 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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