SlrA/SinR/SlrR inhibits motility gene expression upstream of a hypersensitive and hysteretic switch at the level of σ(D) in Bacillus subtilis

Mol Microbiol. 2012 Mar;83(6):1210-28. doi: 10.1111/j.1365-2958.2012.08003.x. Epub 2012 Feb 22.


Exponentially growing Bacillus subtilis cultures are epigenetically differentiated into two subpopulations in which cells are either ON or OFF for σ(d) -dependent gene expression: a pattern suggestive of bistability. The gene encoding σ(D) , sigD, is part of the 31-gene fla/che operon where its location at the 3' end, 25 kb away from the strong P(fla/che) promoter, determines its expression level relative to a threshold. Here we show that addition of a single extra copy of the slrA gene in the chromosome inhibited σ(d) -dependent gene expression. SlrA together with SinR and SlrR reduced sigD transcript by potentiating a distance-dependent decrease in fla/che operon transcript abundance that was not mediated by changes in expression from the P(fla/che) promoter. Consistent with acting upstream of σ(D) , SlrA/SinR/SlrR was bypassed by artificial ectopic expression of sigD and hysteretically maintained for 20 generations by engaging the sigD gene at the native locus. SlrA/SinR/SlrR was also bypassed by increasing fla/che transcription and resulted in a hypersensitive output in flagellin expression. Thus, flagellin gene expression demonstrated hypersensitivity and hysteresis and we conclude that σ(d) -dependent gene expression is bistable.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacillus subtilis / genetics
  • Bacillus subtilis / metabolism*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Down-Regulation*
  • Gene Expression Regulation, Bacterial
  • Molecular Sequence Data
  • Operon
  • Promoter Regions, Genetic
  • Sigma Factor / genetics
  • Sigma Factor / metabolism*
  • Transcription, Genetic


  • Bacterial Proteins
  • Sigma Factor