Structure, Biogenesis and Mode of Action of Pyoverdins

Iron with rare exceptions is available to microorganisms only in its trivalent form. Due to the low dissociation constants of its various oxide hydrates the concentration of free Fe3+ at pH 7.0 is at best 10-17 mole/liter while about 10-6 mole/liter would be needed to maintain the necessary supply for the living cells. Soil bacteria as well as those infesting animals or man (where the Fe3+ supply is limited due to binding to peptidic complexing substances) form a variety of complexing agents (usually called siderophores) capable to bind Fe3+ or secure it by transcomplexation.