The objective of this research is to understand the detailed molecular mechanisms by which microorganisms sequester iron. Research in this area has previously concentrated on a group of compounds, called siderophores, which chelate ferric ion and transport it into the cells via specific transport systems. However, it is well known that microorganisms can also assimilate the metal from a wide variety of other complexes, such as citric acid and siderophores from non-related organisms. Recent work in our laboratory strongly suggests that often this non-specific uptake involves reduction of the metal to the ferrous state followed by translocation of the metal into the cell with the organic ligand remaining extracellular. Virtually nothing is known about the detailed mechanism of this process. This research would establish the reductive mechanism as general in the microbial kingdom and address questions of the specificity of the system, i.e., can other metals be reduced and is iron octahedrally coordinated to oxygen ligands required. What is the source of electrons for the extracellular reduction? Are membrane-associated ferrireductases involved? Isotopic iron will be complexed to a variety of organic ligands and tested with several unrelated organisms to establish the generality of the process. An appropriate organism, probably E. coli, will be chosen to examine the details. Membrane preparations will be examined for their ability to reduce ferric chelates, and the enzyme responsible will be purified. We will also examine the possibility that fungal esterases, which have been shown to be sensitive to sulfhydryl reagents, act as ferrireductases in the presence of an electron source. There is increasing evidence that iron acquisition plays an important role in the course of bacterial and fungal infections in man, and for this reason research in the role of siderophores in microbial iron transport has become increasingly clinically relevant. However, the finding that microorganisms possess a reductive mechanism of iron transport, which enables them to obtain iron from a host of chelates, puts this area of research in a new light. If chemotherapy based on depriving infecting microorganism of irons is to be truly effective, it will be necessary to understand the mechanism of the reductive transport system also.
