Siderophores Subject

The nature of the tonB mutation required for assimilation of the iron of all known siderophores remains elusive in spite of a continuing discussion of the subject (73, 93, 94). It has recently been reported that tonB mutants are defective in the energy-dependent step in Bi2 transport,... 

Iron is transported in forms in which it is tightly complexed to small chelators called siderophores (microorganisms) or to proteins called transferrins (animals) or to citrate or mugeneic acid (plants). The problem of how the iron is released in a controlled fashion is largely unresolved. The process of mineral formation, called biomineralization, is a subject of active investigation. Vanadium and molybdenum are transported as stable anions. Zinc and copper appear to be transported loosely associated with peptides or proteins (plants) and possibly mugeneic acid in plants. Much remains to be learned about the biological transport of nonferrous metal ions. 

Siderophores are low molecular weight compounds that chelate Fe3+ and transport it into the cell. Competition for iron appears to occur between pseudomonads and the rhizosphere bacteria and fungi. Three unusual siderophores with antifungal activity have been described from fluorescent pseudomonads, pyochelin (9), S-dihydroaeruginoic acid (10) and aeruginoic acid [13]. The importance of siderophores in biological control has been the subject of some debate [14]. 

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