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

Bodil Stentebjerg-Olesen, Trinad Chakraborty, Per Klemm

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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.
Original languageEnglish
JournalF E M S Microbiology Letters
Pages (from-to)319-325
Publication statusPublished - 2000

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