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

Abstract

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 σ-dependent promoter. We showed that in the heterologous host Bacillus subtilis, Cpe1786, renamed IscR, 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. IscR 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 IscR 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 IscR.

Chromosomal Resistance to Metronidazole in Clostridioides difficile Can Be Mediated by Epistasis between Iron Homeostasis and Oxidoreductases

“…Iron-sulfur [Fe-S] clusters are essential to the biochemistry of several proteins that conduct electron transfer reactions (39,40). In pathogenic bacteria the assembly and incorporation of [Fe-S] clusters are mostly controlled by the isc and suf operons, of which isc is the housekeeping system; furthermore, C. difficile lacks the suf operon (41). Holo-IscR binds DNA as a homodimer, but damage to its [4Fe-4S] by reactive free radicals or iron starvation increases cellular levels of apo-IscR, triggering defensive mechanisms, including antioxidants such as cysteine and non-protein thiols (42).…”

“…Further assessment of the function of IscR in resistance. Because IscR has not been previously linked to metronidazole resistance, we further studied its role by focusing on pyruvate-lactate metabolism, which is altered by iscR deletion in Clostridium perfringens (41). Additionally, in B. fragilis with decreased PFOR activity, a shift to lactate fermentation is accompanied by reduced metronidazole activity (51).…”

Chromosomal Resistance to Metronidazole inClostridioides difficilecan be Mediated By Epistasis Between Iron Homeostasis and Oxidoreductases

“…Iron-sulfur [Fe–S] clusters are essential to the biochemistry of several proteins that conduct electron transfer reactions (28, 29). In pathogenic bacteria the assembly and incorporation of [Fe–S] clusters is mostly controlled by the isc and suf operons, of which isc is the house-keeping system; furthermore, C. difficile lacks the suf operon (30). Holo-IscR binds DNA as a homodimer, but damage to its [4Fe-4S] by reactive free radicals or iron-starvation increases cellular levels of apo-IscR, triggering defensive mechanisms including antioxidants such as cysteine and non-protein thiols (31).…”

Transcriptional regulation of the Pseudomonas aeruginosa iron-sulfur cluster assembly pathway by binding of IscR to multiple sites

“…The ability to identify IscR Type-1 binding sites in bacterial genomes is an important tool for the analysis of IscR global regulation of gene expression. The availability of characterized IscR Type-1 binding sites from different bacteria, including Clostridium perfringens [43], E . coli [19, 20, 22, 44], Erwinia chrysanthemi [26], Klebsiella pneumoniae [27, 45], Thylacinus potens [42], Xanthomonas campestris [14], and P .…”