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All microorganisms with an exception to been some lactobacilli require iron employed as a cofactor by many metabolic enzymes and regulatory proteins because of its characteristic, two stable oxidation states Fe2+ (ferrous form) and Fe3+(ferric form). Although the iron is abundant in the environment yet the iron is a limiting factor for bacterial growth because it forms insoluble ferric hydroxide complexes under aerobic conditions and neutral pH.

The bacteria have developed specialised high affinity transport system to acquire sufficient amount of iron. Most bacteria bear the ability to produce and secrete molecules called siderophores (means iron bearers, in Greek). The siderophores are special iron chelating agents which help in solubilization and uptake of iron. Siderophores are water soluble low molecular weight (500 — 1500 Da) molecules which bind with ferric iron with great affinity.

There are two main categories of siderophores which have been studied extensively. Phenolcatechol derivatives are synthesized by enterobacteria and have been given common names enterochelin and enterobactin. These systems carry iron into the cell.

There is system to monitor the intracellular level of iron in the bacterial cell. The iron deficiency leads to excretion of siderophores. The shortage of iron in bacterial cell will bring down the growth while high concentrations of iron are toxic to bacterial cells.

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