Environmental iron is mostly in a form (the 3+ oxidation state) that is characterized by extreme insolubility at biological pH. In order to dissolve iron, many bacterial and fungal species synthesize a line of relatively low molecular weight, virtually ferric-specific chelating, or binding, agents generically called siderophores (Gr. “iron bearer,” ISI Atlas of Science: Biochemistry, 1, 53-6, 1988). The affinity of siderophores for iron (III) is such that they can compete effectively with hydroxyl ion for the metal. Microorganisms have also evolved highly efficient transport systems for ferric siderophores that enable them to recognize trace amounts of the complexed metal ion and make it available to metabolic demands within the cell.
A remarkable feature of the siderophore biosynthesis an transport pathway is its ability to adapt to the external level of iron At less than molecular concentrations in the growth medium, the systems are usually fully induced whereas at iron ...
