FimE-catalyzed Off-To-On Inversion of the Type 1 Fimbrial Phase Switch and Insertion Sequence Recruitment in an Escherichia Coli K-12 fimB Strain

FEMS Microbiol Lett. 2000 Jan 15;182(2):319-25. doi: 10.1111/j.1574-6968.2000.tb08915.x.


We have investigated the capacity of a well-defined Escherichia coli fimB strain, AAEC350 (a derivative of MG1655), to express type 1 fimbriae under various growth conditions. The expression of type 1 fimbriae is phase-variable due to the inversion of a 314-bp DNA segment. Two tyrosine recombinases, FimB and FimE, mediate the inversion of the phase switch. FimB can carry out recombination in both directions, whereas the current evidence suggests that FimE-catalyzed switching is on-to-off only. We show here that AAEC350 is in fact capable of off-to-on phase switching and type 1 fimbrial expression under aerobic static growth conditions. The phase switching is mediated by FimE, and allows emerging fimbriate AAEC350 to outgrow their non-fimbriate counterparts by pellicle formation. Following inversion of the phase switch, this element can remain phase-locked in the on orientation due to integration of insertion sequence elements, viz. IS1 or IS5, at various positions in either the fimE gene or the phase switch.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agglutination
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Culture Media
  • DNA Transposable Elements
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Escherichia coli / genetics*
  • Escherichia coli / growth & development
  • Escherichia coli / metabolism
  • Escherichia coli / ultrastructure
  • Escherichia coli Proteins*
  • Fimbriae, Bacterial / metabolism*
  • Gene Expression Regulation, Bacterial*
  • Integrases*
  • Polymerase Chain Reaction / methods
  • Recombination, Genetic
  • Sequence Analysis, DNA


  • Bacterial Proteins
  • Culture Media
  • DNA Transposable Elements
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • fimB protein, E coli
  • fimE protein, E coli
  • Integrases