Bistability in the Bacillus subtilis K-state (competence) system requires a positive feedback loop

Mol Microbiol. 2005 May;56(3):615-24. doi: 10.1111/j.1365-2958.2005.04592.x.


High expression of the transcriptional activator ComK occurs in 10-20% of the cells in stationary phase cultures of Bacillus subtilis strain 168. ComK drives the expression of more than 100 genes constituting the semidormant K-state, distinct from sporulation and vegetative growth. Among the genes so activated are those that permit competence for genetic transformation. We have addressed the origin of bistability in expression of ComK. We show that bistability requires positive autoregulation at the promoter of comK, but not a potential toggle switch, in which ComK represses the promoter of rok and Rok represses the promoter of comK. We further address the source of the noise that results in the stochastic selection of cells that will express comK. A revised model for the regulation of comK expression is proposed that partially explains bistability.

Publication types

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

MeSH terms

  • Adaptation, Physiological / genetics
  • Bacillus subtilis / genetics*
  • Bacillus subtilis / physiology
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Feedback, Physiological*
  • Gene Expression Regulation, Bacterial*
  • Homeostasis
  • Mutation
  • Promoter Regions, Genetic
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism*
  • Transformation, Bacterial / genetics
  • beta-Galactosidase / genetics
  • beta-Galactosidase / metabolism


  • Bacterial Proteins
  • DNA-Binding Proteins
  • Repressor Proteins
  • Transcription Factors
  • comK protein, Bacillus subtilis
  • beta-Galactosidase