Growth conditions mediate differential transcription of fim genes involved in phase variation of type 1 pili

Abstract

Type 1 pili in Escherichia coli undergo phase variation in which individual cells in a population reversibly switch between piliated (Pil+) and nonpiliated (Pil-) states. The switching process is mediated by an invertible DNA fragment which contains the promoter for fimA, the gene encoding the major structural subunit of type 1 pili. Although type 1 pili randomly phase vary in broth cultures, many clinical isolates of E. coli do not express type 1 pili when cultured on agar media. We investigated the role of the invertible element and the upstream genes, fimB and fimE, in the agar-mediated suppression of pili in an agar-negative clinical isolate, strain 149. Southern hybridization and polymerase chain reaction analyses of the fimA promoter region in broth-grown 149 cells indicated that the invertible element was present in orientations corresponding to both Pil+ and Pil- phenotypes. In contrast, only one orientation of the invertible element, corresponding to the Pil- phenotype, was observed in strain 149 cells cultured on agar. A second clinical isolate, strain 2-7, which expresses type 1 pili on agar was also examined; the invertible element was found in both the Pil+ and Pil- orientations during growth of this strain on agar as well as in broth. The introduction of the fim gene cluster from strain J96 on a multicopy plasmid into agar-negative strain 149 resulted in the production of both J96 and 149 pili during growth on agar. Experiments with subclones of the J96 genes indicated that the presence of an intact fimB gene allowed strain 149 pili to be produced on agar. Differences in pilus production between agar and broth cultures appear to be the result of differential transcription of fimB and fimE under the two growth conditions. In contrast, the pattern of expression of these genes in agar phase-variable strain 2-7 did not differ between broth- and agar-grown cells.

Environmental regulation of the fim switch controlling type 1 fimbrial phase variation in Escherichia coli K-12: effects of temperature and media

“…It has been clearly shown that at least some of these effects reflect strong selection for or against fimbriate bacteria. Several authors have suggested that liquid and agar represent different environments that result in differential regulation of the fim switch (22,43). We have measured switching frequencies both on agar and in liquid media and found no obvious differences in control.…”

The Flagellar Sigma Factor FliA Regulates Adhesion and Invasion of Crohn Disease-associated Escherichia coli via a Cyclic Dimeric GMP-dependent Pathway

“…We used a PCR-based approach (38) to confirm that the deficiency in type 1 pili resulted from the shift of the DNA invertible element orientation toward the phase-OFF orientation (Fig. 1C).…”

In vivo detection of Escherichia coli type 1 fimbrial expression and phase variation during experimental urinary tract infection

“…Two recombinases encoded by the fim cluster, FimB and FimE, mediate the inversion of the invertible element (Klemm, 1986). Several elements regulating the expression of FimB and FimE and the sensitivity of the invertible element towards switching, including environmental factors such as temperature and growth media, have been identified (Old & Duguid, 1970 ;Schwan et al, 1992 ;Blomfield et al, 1993 ;Gally et al, 1993 ;Newman et al, 1994 ;Olsen et al, 1998).…”