Bistability and biofilm formation in Bacillus subtilis

Mol Microbiol. 2008 Jan;67(2):254-63. doi: 10.1111/j.1365-2958.2007.06040.x. Epub 2007 Nov 28.


Biofilms of Bacillus subtilis consist of long chains of cells that are held together in bundles by an extracellular matrix of exopolysaccharide and the protein TasA. The exopolysaccharide is produced by enzymes encoded by the epsA-O operon and the gene encoding TasA is located in the yqxM-sipW-tasA operon. Both operons are under the control of the repressor SinR. Derepression is mediated by the antirepressor SinI, which binds to SinR with a 1:1 stoichiometry. Paradoxically, in medium promoting derepression of the matrix operons, the overall concentration of SinR in the culture greatly exceeded that of SinI. We show that under biofilm-promoting conditions sinI, which is under the control of the response regulator Spo0A, was expressed only in a small subpopulation of cells, whereas sinR was expressed in almost all cells. Activation of Spo0A is known to be subject to a bistable switch, and we infer that SinI reaches levels sufficient to trigger matrix production only in the subpopulation of cells in which Spo0A is active. Additionally, evidence suggests that sinI is expressed at intermediate, but not low or high, levels of Spo0A activity, which may explain why certain nutritional conditions are more effective in promoting biofilm formation than others.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacillus subtilis / cytology
  • Bacillus subtilis / genetics
  • Bacillus subtilis / physiology*
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biofilms / growth & development*
  • Culture Media / analysis
  • Gene Expression Regulation, Bacterial
  • Operon
  • Polysaccharides, Bacterial / genetics
  • Polysaccharides, Bacterial / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / isolation & purification
  • Recombinant Fusion Proteins / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / isolation & purification
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • Bacterial Proteins
  • Culture Media
  • Polysaccharides, Bacterial
  • Recombinant Fusion Proteins
  • Repressor Proteins
  • SinI protein, Bacillus subtilis
  • Spo0A protein, Bacillus subtilis
  • Transcription Factors
  • FlaD protein, Bacteria