Microbial Iron Transport Structure and Function of Siderophores

Abstract

The extreme insolubility of iron limits the supply of most organisms by this metal which forms an essential part of enzymes active in the energy-generating electron transport chains and of the intermediary metabolism. The article emphasizes the intricate mechanisms by which microbes, bacteria as well as fungi, overcome iron deficiency imposed by the human host. In humans extracelluar iron is almost exclusively bound to transferrin and lactoferrin. To withdraw iron from these proteins most microbes secrete siderophores which exert an extremely high affinity and selectivity for iron (III). In addition, they posess unique transport systems by which the iron(III)-siderophores are actively transported into the microbial cells. Upon infection the human host actively reduces the iron available to microbes. The unique properties render iron (III) a suitable target for the host to control microbial growth (“nutritional immunity”). Interference with siderophore biosynthesis is considered as a therapeutic means to treat microbial infections. Highly effective antibiotics are known which contain a siderophore as carrier of the antimicrobially active moiety. A siderophore is used to remove iron which has accumulated in the body as a consequence of iron overload diseases.