Epigenetic phase variation of the pap operon in Escherichia coli

ABSTRACT The occurrence of unilateral flagellar phase variation was previously demonstrated in Escherichia coli strains carrying the non-fliC flagellin-specifying locus flk. In this study, we investigated the mechanism involved in this process. By using sequencing and sequence analysis, the flk region between the chromosomal genes yhaC and rnpB was characterized in all described flk-positive E. coli strains, including the H35 strain identified in this study (the other strains used are H3, H36, H47, and H53 strains), and this region was found to contain a putative integrase gene and flanking direct repeats in addition to the flk flagellin-specifying gene flkA and a fliC repressor gene, flkB, indicating that there is a typical genomic islet (GI), which was designated the flk GI. The horizontal transfer potential of the flk GI was indicated by detection of the excised extrachromosomal circular form of the flk GI. By generating fliC-expressing variants of H3 and H47 strains, unilateral flagellar phase variation in flk-positive strains was shown to be mediated by excision of the flk GI. The function of the proposed integrase gene was confirmed by deletion and a complementation test. The potential integration sites of the flk GI were identified. A general model for flagellar phase variation in flk-positive E. coli strains can be expressed as fliC off + flkA on → fliC on + flkA none. This is the first time that a molecular mechanism for flagellar phase variation has been reported for E. coli.

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Regulation of P-Fimbrial Phase Variation Frequencies in Escherichia coli CFT073

Infection and Immunity ◽

10.1128/iai.01989-06 ◽

2007 ◽

Vol 75 (7) ◽

pp. 3325-3334 ◽

Cited By ~ 30

Author(s):

Nicola Holden ◽

Makrina Totsika ◽

Lynn Dixon ◽

Kirsteen Catherwood ◽

David L. Gally

Keyword(s):

Escherichia Coli ◽

Phase Transition ◽

Regulatory Region ◽

Phase Variation ◽

Culture Conditions ◽

Host Tissue ◽

Clinical Isolates ◽

E Coli ◽

K 12 ◽

First Time

ABSTRACT Adherence of uropathogenic Escherichia coli to host tissue is required for infection and is mediated by fimbriae, such as pyelonephritis-associated pili (Pap). Expression of P fimbriae is regulated by phase variation, and to date, phase transition frequencies have been measured only for pap regulatory region constructs integrated into the E. coli K-12 chromosome. The aim of this work was to measure P phase transition frequencies in clinical isolates for the first time, including frequencies for the sequenced strain E. coli CFT073. P fimbriation and associated phase transition frequencies were measured for two E. coli clinical isolates and compared with levels for homologous pap constructs in E. coli K-12. Fimbriation and off-to-on transition frequencies were always higher in the clinical isolate. It was concluded that the regulatory inputs controlling papI expression are likely to be different in E. coli CFT073 and E. coli K-12 as (i) phase variation could be stimulated in E. coli K-12 by induction of papI and (ii) the level of expression of a papI::gfp + fusion was higher in E. coli CFT073 than in E. coli K-12. Furthermore, phase transition frequencies for the two E. coli CFT073 pap clusters were shown to be different depending on the culture conditions, indicating that there is a hierarchy of expression depending on signal inputs.

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