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Abstract Background The bioavailability of iron is quite low since it is usually present as insoluble complexes. To solve the bioavailability problem microorganisms have developed highly efficient iron-scavenging systems based on the synthesis of siderophores that have high iron affinity. The systems of iron assimilation in microorganisms are strictly regulated to control the intracellular iron levels since at high concentrations iron is toxic for cells. <it>Streptomyces pilosus </it>synthesizes the siderofore desferrioxamine B. The first step in desferrioxamine biosynthesis is decarboxylation of L-lysine to form cadaverine, a desferrioxamine B precursor. This reaction is catalyzed by the lysine decarboxylase, an enzyme encoded by the <it>desA </it>gene that is repressed by iron. Results The binding of the DmdR (acronym for divalent metal dependent repressor) to the <it>desA </it>promoter in presence of Fe2+ or other divalent ions has been characterized. A 51 bp DNA fragment of the <it>desA </it>promoter containing the 9 bp inverted repeat was sufficient for binding of the DmdR repressor, as observed by the electrophoretic mobility shift assay. The <it>desA </it>mobility shift was prevented by neutralizing DmdR with anti-DmdR antibodies or by chelating the divalent metal in the binding reaction with 2,2'-dipyridyl. Binding to the <it>desA </it>promoter was observed with purified DmdR repressors of <it>Streptomyces coelicolor </it>or <it>Rhodococcus fascians </it>suggesting that there is a common mechanism of iron-regulation in actinomycetes. The complete <it>desA </it>promoter region was coupled using transcriptional fusions to the <it>amy </it>reporter gene (encoding α-amylase) in low copy or multicopy <it>Streptomyces </it>vectors. The iron-regulated <it>desA </it>promoter was induced by addition of the iron chelating agent 2,2'-dipyridyl resulting in a strong expression of the reporter gene. Conclusions The iron-regulated <it>desA </it>promoter can be used for inducible expression of genes in <it>Streptomyces </it>species, as shown by de-repression of the promoter when coupled to a reporter gene.</p

Characterization of the iron-regulated desA promoter of Streptomyces pilosus as a system for controlled gene expression in actinomycetes.