The high affinity, siderophore mediated iron assimilation systems of prokaryotic and eukaryotic microorganisms will be investigated by application of the standard techniques of molecular genetics. The biosynthesis and transport components of the cloned, plasmid-derived, aerobactin system of hospital isolates of Escherichia coli will be defined. Definitive proof for the pathway from lysine to N omega-hydroxylysine to aerobactin will be sought and the enzymes characterized. The nature of the transcriptional regulation of this system by iron will be studied to determine if the message accumulated at low iron results from iron-repressor binding to the promoter-operator or, alternatively, from altered rates of turnover of the mRNA. Preliminary experiments will be aimed at cloning all or part of the rhodotorulic acid siderophore system of the basidiomycetous yeast Rhodotorula pilimanae.