Microbial siderophores as molecular shuttles for metal cations: sources, sinks and application perspectives.

Iron is one of the highly abundant elements on the earth's crust, an essential micronutrient for a majority of life forms, and exists in two frequent oxidation states such as ferrous (Fe) and ferric (Fe). These two oxidation states are interconvertible by redox reactions and form complexes with a wide range of siderophores. At neutral pH in soil, Fe is highly soluble upto 100 mM but have less biological value, whereas Fe is less soluble upto 10 M.