Disruption of the siderophore-binding desE receptor gene in Streptomyces coelicolor A3(2) results in impaired growth in spite of multiple iron-siderophore transport systems

Abstract

Ferrioxamines-mediated iron acquisition by Streptomyces coelicolor A3(2) has recently received increased attention. In addition to the biological role of desferrioxamines (dFOs) as hydroxamate siderophores, and the pharmaceutical application of dFO-B as an iron-chelator, the ferrioxamines have been shown to mediate microbial interactions. In S. coelicolor the siderophore-binding receptors DesE (Sco2780) and CdtB (Sco7399) have been postulated to specifically recognize and uptake FO-E (cyclic) and FO-B (linear) respectively. Here, disruption of the desE gene in S. coelicolor, and subsequent phenotypic analysis, is used to demonstrate a link between iron metabolism and physiological and morphological development. Streptomyces coelicolor desE mutants, isolated in both wild-type (M145) and a coelichelin biosynthesis and transport minus background (mutant W3), a second hydroxamate siderophore system only found in S. coelicolor and related species, resulted in impaired growth and lack of sporulation. This phenotype could only be partially rescued by expression in trans of either desE and cdtB genes, which contrasted with the ability of FO-E, and to a lesser extent of FO-B, to fully restore growth at µM concentrations, with a concomitant induction of a marked phenotypic response involving precocious synthesis of actinorhodin and sporulation. Moreover, growth restoration of the desE mutant by complementation with desE and cdtB showed that DesE, which is universally conserved in Streptomyces, and CdtB, only present in certain streptomycetes, have partial equivalent functional roles under laboratory conditions, implying overlapping ferrioxamine specificities. The biotechnological and ecological implications of these observations are discussed.