Iron siderophores are low molecular weight (400-1500 Da) ferric ion binding proteins. Bacteria ( Escherichia coli, Salmonella, Klebsiella pneumoniae, Vibrio cholerae, Vibrio anguillarum, Aeromonas, Aerobacter aerogens, Enterobacter, Yersinia and Mycobacterium sp.), fungi ( Aspergillus nidulans, A. versicolor, Penicillium chrysogenum, P. citrinum, Mucor, Rhizopus, Trametes versicolor, Ustilago sphaerogina, Saccharomyces cerivisiae, Rhodotorula minuta and Debaromyces sp.) and actinomycetes (Actinomadura madurae, Nocardia asteroids and Streptomyces griseus) were reported to produce different types of siderophores (Kannahi and Senbagam, 2014). Around 500 iron siderophores are reported to date (Boukhalfa & Crumbliss, 2002) from bacteria, fungi, actinomycetes and plants.
Types of iron siderophores
| SN. | Types of iron siderophores | Representative microorganisms | References | |
| 1 | Hydroxamate | |||
| Ferrichrome | Ustilago sphaerogena (Fungi) | Messenger and Ratledge, 1985 | ||
| Ferribactin | Pseudomonas fluorescens | |||
| Gonobactin and Nocobactin | Neisseria gonorrhoeae and N. meningitids | |||
| 2 | Catecholate (Phenolates) | |||
| Enterochelin | E. coli, S. typhimurium and K. pneumonia | |||
| Agrobactin | Agrobacterium tumefaciens | |||
| Parabactin | Paracoccus denitrificans | |||
| Catecholates | Erwinia carotovora | Leong and Neilands, 1982 | ||
| 3 | Carboxylate (complexones) | |||
| Rhizobactin | Rhizobium meliloti | |||
(Note - data were adopted from Ali and Vidhale, 2013)
Iron is the verdant element in the earth crust, most often present as goethite, hematite and ferrihydrite (oxide and hydroxide form of ferric ion that are responsible for red and yellow soil colors). It is an essential micronutrient for almost all organisms, including bacteria, fungi and plants. However lactic acid bacterial community is able to grow in the absence of iron (Bruyneel et al., 1989).
Iron chelating siderophores posses clinical (human pathogenesis), agricultural (iron uptake in plants) and environmental (excess iron chelators) applications.
In the human body, iron is buried inside the iron holding proteins (such as transferrin, lactoferrin and ferritin). These iron complexes are unavailable for pathogenic bacteria that infect human body. But the pathogenic microbes are able to produce siderophores to chelate ferric iron (Fe3+). These microbial siderophores conduce to take out iron from iron holding proteins (Wooldridge and Williams, 1993) and further contribute towards pathogenic virulence mechanism. For example, the anthrax pathogen Bacillus anthracis releases two siderophores- bacillibactin and petrobactin to scavenge ferric iron from iron binding proteins (Abergel et al., 2006). Apart from this, siderophore form Klebsiella pneumonia has been reported to act as anti-malarial agent (Gysin et al., 1991). Another siderophore (Desferrioxamine B) produced by Streptomycespilosus has significant activity against Plasmodium falciparum (protozoic parasite responsible for malaria). Usually siderophore enters inside P. falciparum cell and imbibe intracellular iron.
Plants reduce Fe (III) complexes (also called Fe3+ or ferric complexes) to oxidized Fe (II) ions (also called Fe2+ or ferrous ions) at the root surface (via siderophore producing microbial community associated with plant root system) and then uptake iron (Fe2+) as micronutrient for cellular metabolism and growth (Loper and Buyer, 1991; Loper and Henkels, 1999). In case of plant iron deficiency, graminaceous plants (grasses, cereals and rice) secrete phytosiderophores into the soil to make bioavailable form of iron (ferric to ferrous ions) for plant root system (Sugiura and Nomoto, 1984). Apart from siderophores, lower pH also favor iron uptake in plants.
These siderophore proteins could be used to remove excess iron from the water. Iron utilizing industries are usually expelling their waste water in river or in soil. Thus iron compounds are accumulated in ecosystem. Excess iron becomes harmful to human beings. Iron or its compounds enter inside human body via drinking water or by food stuff. According to Iron Disorders Institute (situated at Greenville, South Carolina) when level of iron exceed in vital organs, increases the risk for liver disease (cirrhosis, cancer), heart attack or heart failure, diabetes mellitus, osteoarthritis, osteoporosis, metabolic syndrome, hypothyroidism, hypogonadism, premature death, accelerate neurodegenerative diseases (such as Alzheimer’s, early-onset Parkinson’s, Huntington’s, epilepsy and multiple sclerosis).
Rhizosphere soil organisms produce siderophores to improve the plant growth. On other hand, some siderophores are able to inhibit the growth of plant pathogen. In humans, pathogenic microorganisms use siderophores for the acquisition of iron as their nutrition form human body. Some siderophores act as anti-malarial drug (Gysin et al., 1991) and siderophores (such as dexrazoxane, O-trensox, desferriexochelins, desferrithiocin, tachpyridine) inhibit the growth of cancer cells (Miethke and Marahiel, 2007). Apart from this, siderophores are used to remove iron compounds form water.
References
Abergel R.J., Wilson M.K., Arceneaux J.E.L., Hoette T.M., Strong R.K., Byers B.R., and Raymond K.N., (2006) Anthrax pathogen evades the mammalian immune system through stealth siderophore production. PNAS 103 (49): 18499â€"18503.
Ali S.S. and Vidhale N.N., (2013) Bacterial Siderophore and their Application: A review. Int. J. Curr. Microbiol. App. Sci, 2(12): 303-312.
Boukhalfa H. and Crumbliss A.L., (2002) Chemical aspects of siderophore mediated iron transport. Biometals, 15, 325-339.
Bruyneel B., Vandewoestyne M. and Verstraete W., (1989) Lactic acid bacteria: microorganisms able to grow in the absence of available iron and copper. Biotechnol. Lett. 11:401-406.
Gysin et al., (1991) Siderophores as anti parasitic agents. US patent. 5, 192-807.
Kannahi M. and Senbagam N., (2014) Studies on siderophore production by microbial isolates obtained from rhizosphere soil and its antibacterial activity, Journal of Chemical and Pharmaceutical Research, 6(4):1142-1145.
Leong S.A. and Neilands J.B., (1982) Siderophore production by phytopathogenic microbial species. Arch. Biochem. Biophys. 281, 351-359.
Loper J. E. and Buyer J. S., (1991) Siderophores in microbial interactions of plant surfaces. Mol. Plant-Microbe Interact. 4, 5-13.
Loper J.E. and Henkels M.D., (1999) Utilization of heterologous siderophore enhances levels of iron available to Pseudomonas putida in the rhizosphere. Applied Environmental Microbiology. 65, 5357-5363.
Messenger A.J.M. and Ratledge C., (1985) Siderophores: Comprehensive Biotechnology, Edited by M MooYoung (Pergamon press, New York), pp. 275-295.
Miethke M. and Marahiel M. A., (2007) Siderophore-Based Iron Acquisition and Pathogen Control. Microbiol Mol Biol Rev. 71(3), 413 51.
Sugiura Y. and Nomoto K., (1984) Phytosiderophores structures and properties of mugineic acids and their metal complexes. Structure and Bonding, 58: 107â€"135.
Wooldridge K.G. and Williams P.H., (1993) Iron uptake mechanism of pathogenic bacteria. FEMS Microbiol. Rev. 12, 325- 348.
About Author / Additional Info:
Research Scholar,
Department of Biotechnology, NIT Raipur
Research Interest: Bio-fuels and biological waste water treatment