Siderophores properties, mechanism and preparation

2. Role of siderophores
 High affinity system of Fe3+ acquisition, utilization
and storage.
 Sometimes, required for virulence.
 Helps in growth, colonization and asexual
sporulation.
 Elicit the plant defense through an antagonism
mechanism between SA and JA signaling cascades.
2

3. MECHANISM OF IRON ACQUISTION
BACTERIA
FUNGI
Reduction of Fe(III) to Fe(II)
Direct acquisition
By iron binding proteins
ferric siderophores
Siderophore-mediated Fe3+ uptake
RIA (reductive iron assimilation)
heme uptake
direct Fe2+ uptake
3

4. Mechanism of siderophore mediated iron uptake
inbacteria
(Syed Sajeed Ali, 2013) 4

5. Postulated fungal siderophore biosynthetic pathway
NRPS (Nonribosomal Peptide Synthetase) : Large multifunctional
enzymes that synthesize peptides from proteinogenic and
nonproteinogenic precursors independently of the ribosome. 5

6. Detection of siderophore production
• widely used method for detection of
siderophore production by microorganisms in
solid medium is the universal chrome azurol S
(CAS)-agar plate assay.
6

7. 7

8. Types of siderophores
• Hydroxamate,
• Catecholate and
• Carboxylate
8

9. Hydroxamate
• Hydroxamate group-bearing siderophores are mainly
synthesized by fungi and Gram-positive filament-
forming bacteria (streptomycetes).
• In fungal systems the hydroxamic acid chelating
group is commonly derived from acylated Nδ-acyl-
Nδ-hydroxy-L-ornithine.
9

10. Catecholate
• Each catecholate group provides two oxygen atoms for
chelation with iron so that a hexadentate octahedral complex is
formed as in the case of the hydroxamate siderophores. Linear
catecholate siderophore are also produced in certain species.
• Agrobactin and parabactin are produced by Agrobacterium
tumefaciens and Paracoccus denitrificans respectively.
10

11. Carboxylate
• The best characterized carboxylate type siderophore with a
novel structure is rhizobactin.
• Rhizobactin is produced by Rhizobium meliloti strain DM4
and is an amino poly (carboxylic acid) with
ethylenediaminedicarboxyl and hydroxycarboxyl moieties as
ironchelating groups.
• Staphyloferrin A, produced by Staphylococcus hyicus
DSM20459, is another member of this class of complexon
siderophores.
11

12. Siderophore structure in bacteria
12

13.  All fungal siderophores identified so far are hydroxamates
 Fungal hydroxamates are derived from the
nonproteinogenic amino acid ornithine and different acyl
groups,
 grouped into four structural families
(I) Rhodotorulic acid
(ii) Fusarinines
(iii) Coprogens
(iv) Ferrichromes
SIDEROPHORES
IN PLANT PATHOGENIC FUNGI
13

14. Representative fungal siderophores, Peptide and ester bonds separating
N5 – acyl- N5- hydroxyornithine 14

15. Characterized Pathogenic Fungal Siderophore NRPS
NRPS name Fungal species Siderophores Reference
Ferrichrome NRPS
Sid2 U. maydis Ferrichrome Yuan et al., 2001
Nps2 C. heterostrophus Ferricrocin Oide et al., 2007
Nps2 F. graminearum Ferricrocin Oide et al., 2007
Ssm1 M. grisea Ferricrocin Hof et al., 2007
SidFA/Fer3 U. maydis Ferrichrome A Eichhorn et al., 2006
Coprogen NRPS
Nps6 A.brassicicola N-dimethylcoprogen Oide et al., 2006
Nps6 C.heterostrophus Coprogen Oide et al., 2006
Nps6 C.miyabeanus nd Oide et al., 2006
Fusarinine NRPS
Nps6 F.graminearum Fusarinine C Oide et al., 2006
15

16. Mechanism of siderophores in bio
control of plant pathogens
• Siderophores produced by a microorganism can bind iron with
high specificity and affinity, making the iron unavailable for
other microorganisms; thereby limiting their growth.
• Competition for iron by siderophore production is an
important antagonistic trait found in many of the bacterial bio
control agents against plant pathogens.
• Microbial siderophores may stimulate plant growth directly by
increasing the availability of iron in the soil surrounding the
roots or indirectly by competitively inhibiting the growth of
plant pathogens with less efficient iron-uptake systems.
16

17. IRON – AN IMPORTANT ESSENTIAL ELEMENT
 Iron is a constituent of protein.
 It activates the number of enzymes.
 Iron is a vital element require by all living organisms for
many cellular processes such as electron transport chain and as
a cofactor for many enzymes
 It plays an essential role in the nucleic acid metabolism.
 It is necessary for synthesis and maintenance of chlorophyll in
plants.

18.  Siderophores are compounds from ancient Greek words, sidero
‘iron’ and phore ‘carriers’ meaning ‘iron carriers’.
 These are low-molecular-weight iron-chelating compounds,
produced by ‘rhizospheric bacteria’ under iron-limited conditions.
 They are small, high affinity iron chelating compounds secreted
by microorganisms such as bacteria, fungi etc.
 Siderophore usually form a stable hexahendate, octahedral
complex with Fe3+
 Kloepper et al.(1980) were the first to demonstrate the importance
of Siderophores.
Siderophores

19. TYPES OF SIDEROPHORE
 Hydroxymate siderophore.
eg- Pseudomonas fluorescens
 Catecholate siderophore
eg-Azotobacter vinelandi
 Carboxylate siderophore
eg- Rhizobium meliloti

22. HOW SIDEROPHORES WILL FORM???
Cells produce
siderophores
Iron binds to
siderophore
complex
Siderophore
binds to
recognition site
on cell
Iron is reduced
(Fe3+
into Fe )
2+
Iron is often
insoluble
(oxides,
hydroxides)
Iron is taken up
by the cell.

23. Siderophore
Siderophore receptor site on cell
Outside the Cell
Inside the Cell
Fe
3+

24. Siderophore receptor site on cell
Outside the Cell
Fe
3+
Fe
3+
Inside the Cell

25. Siderophore receptor site on cell
Fe
3+
Fe
3+
Siderophore
Outside the Cell
Fe
3+
Inside the Cell

27. SIDEROPHORE PRODUCING MICROORGANISM
• Azotobacter
• Pseudomonas
• Bacillus
• Streptomyces
•Among thesemicrobes Pseudomonas species isthe activesiderophore
producer

28. DETECTION OF SIDEROPHORE PRODUCTION
Widely used method for detection of siderophore
production by microorganisms in solid medium is
the universal Chrome azurol S (CAS) agar plate
assay.

29. APPLICATION OF SIDEROPHORE

30. Role of Siderophore in Agriculture
 Soil mineral weathering
 Enhancing Growth of plant
 Pathogen Biocontrol of plants