Analysis of theCorynebacterium diphtheriaeDtxR Regulon: Identification of a Putative Siderophore Synthesis and Transport System That Is Similar to theYersiniaHigh-Pathogenicity Island-Encoded Yersiniabactin Synthesis and Uptake System

Abstract

The diphtheria toxin repressor, DtxR, is a global iron-dependent regulatory protein in Corynebacterium diphtheriae that controls gene expression by binding to 19-bp operator sequences. To further define the DtxR regulon in C. diphtheriae, a DtxR repressor titration assay (DRTA) was developed and used to identify 10 previously unknown DtxR binding sites. Open reading frames downstream from seven of the newly identified DtxR binding sites are predicted to encode proteins associated with iron or heme transport. Electrophoretic mobility shift assays indicated that DtxR was able to bind to DNA fragments carrying the 19-bp operator regions, and transcriptional analysis of putative promoter elements adjacent to the binding site sequences revealed that most of these regions displayed iron-and DtxR-regulated activity. A putative siderophore biosynthesis and transport operon located downstream from one of the DtxR binding sites, designated sid, is similar to the yersiniabactin synthesis and uptake genes encoded on the Yersinia pestis high pathogenicity island. The siderophore biosynthetic genes in the sid operon contained a large deletion in the C. diphtheriae C7 strain, but the sid genes were unaffected in four clinical isolates that are representative of the dominant strains from the recent diphtheria epidemic in the former Soviet Union. Mutations in the siderophore biosynthetic genes in a clinical strain had no effect on siderophore synthesis or growth in low-iron conditions; however, a mutation in one of the putative transport proteins, cdtP, resulted in reduced growth in iron-depleted media, which suggests that this system may have a role in iron uptake. The findings from this study indicate that C. diphtheriae contains at least 18 DtxR binding sites and that DtxR may affect the expression of as many as 40 genes.

The Iron-Regulated iupABC Operon Is Required for Saprophytic Growth of the Intracellular Pathogen Rhodococcus equi at Low Iron Concentrations

“…Iron-dependent transcriptional regulation of genes required for siderophore biosynthesis and uptake is mediated by DtxR in Corynebacterium (30,35,(44)(45)(46) and the homologous proteins IdeR and DmdR in, respectively, Mycobacterium (1, 15, 16, 40) and Streptomyces (17,22). DtxR complexed with Fe 2ϩ binds to the operator sequences of iron-regulated genes to repress transcription (53).…”

Genomics ofActinobacteria: Tracing the Evolutionary History of an Ancient Phylum

“…Transcription of tox is regulated by the host-encoded diphtheria toxin represssor DtxR and becomes derepressed during iron depletion (181). Iron-dependent regulators of the DtxR family have been detected in many corynebacteria (326) and described as global regulatory proteins in C. diphtheriae and C. glutamicum (48,245). DtxR obviously links expression of the phage-encoded tox gene with the control of iron homeostasis in the bacterial cell, resulting in a complex host-pathogen-phage interaction.…”

At the Crossroads of Bacterial Metabolism and Virulence Factor Synthesis in Staphylococci

“…regulate iron-dependent gene expression using proteins that are orthologous to the diphtheria toxin regulator (DtxR) (e.g., the iron-dependent regulator [IdeR]) (22,195). Similar in function to Fur, these iron-dependent regulators control the biosynthesis and transport of siderophores, metabolism, and the oxidative stress response (25,128,187). In addition, when complexed with iron, DtxR binds as a dimer to a 19-bp palindromic operator sequence of the diphtheria toxin (tox) promoter in C. diphtheria, repressing the transcription of tox (94).…”