Characterization of the SigD regulon of C. difficile and its positive control of toxin production through the regulation of tcdR

PLoS One. 2013 Dec 16;8(12):e83748. doi: 10.1371/journal.pone.0083748. eCollection 2013.


Clostridium difficile intestinal disease is mediated largely by the actions of toxins A (TcdA) and B (TcdB), whose production occurs after the initial steps of colonization involving different surface or flagellar proteins. In B. subtilis, the sigma factor SigD controls flagellar synthesis, motility, and vegetative autolysins. A homolog of SigD encoding gene is present in the C.difficile 630 genome. We constructed a sigD mutant in C. difficile 630 ∆erm to analyze the regulon of SigD using a global transcriptomic approach. A total of 103 genes were differentially expressed between the wild-type and the sigD mutant, including genes involved in motility, metabolism and regulation. In addition, the sigD mutant displayed decreased expression of genes involved in flagellar biosynthesis, and also of genes encoding TcdA and TcdB as well as TcdR, the positive regulator of the toxins. Genomic analysis and RACE-PCR experiments allowed us to characterize promoter sequences of direct target genes of SigD including tcdR and to identify the SigD consensus. We then established that SigD positively regulates toxin expression via direct control of tcdR transcription. Interestingly, the overexpression of FlgM, a putative anti-SigD factor, inhibited the positive regulation of motility and toxin synthesis by SigD. Thus, SigD appears to be the first positive regulator of the toxin synthesis in C. difficile.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • Bacterial Toxins / biosynthesis*
  • Bacterial Toxins / genetics*
  • Base Sequence
  • Binding Sites
  • Clostridioides difficile / genetics*
  • Clostridioides difficile / growth & development
  • Clostridioides difficile / metabolism*
  • Consensus Sequence
  • DNA-Directed RNA Polymerases / metabolism
  • Flagella / genetics
  • Flagella / metabolism
  • Gene Expression Regulation, Bacterial*
  • Gene Silencing
  • Genetic Complementation Test
  • Mutation
  • Phenotype
  • Position-Specific Scoring Matrices
  • Promoter Regions, Genetic
  • Protein Binding
  • Protein Biosynthesis
  • Transcription Initiation Site
  • Transcription, Genetic
  • Transcriptome


  • Bacterial Proteins
  • Bacterial Toxins
  • DNA-Directed RNA Polymerases

Grant support

Funding was provided by the University of Rouen. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.