Cpe1786/IscR of Clostridium perfringens represses expression of genes involved in Fe-S cluster biogenesis

Cpe1786 of Clostridium perfringens is an Rrf2-type regulator containing the three-cysteine residues coordinating a Fe-S in IscR, the repressor controlling Fe-S homeostasis in enterobacteria. The cpe1786 gene formed an operon with iscSU involved in Fe-S biogenesis and tmrU. This operon was transcribed from a σA-dependent promoter. We showed that in the heterologous host Bacillus subtilis, Cpe1786, renamed IscRCp, negatively controlled its own transcription. We constructed an iscR mutant in C. perfringens. We then compared the expression profile of strain 13 and of the iscR mutant. IscRCp controlled expression of genes involved in Fe-S biogenesis, in amino acid or sugar metabolisms, in fermentation pathways and in host compound utilization. We then demonstrated, using a ChIP-PCR experiment, that IscRCp interacted with its promoter region in vivo in C. perfringens and with the promoter of cpe2093 encoding an amino acid ABC transporter. We utilized a comparative genomic approach to infer a candidate IscR binding motif and reconstruct IscR regulons in clostridia. We showed that point mutations in the conserved motif of 29 bp identified upstream of iscR decreased the cysteine-dependent repression of iscR mediated by IscRCp.