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(p)ppGpp regulates type 1 fimbriation of Escherichia coli by modulating the expression of the site-specific recombinase FimB.
Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
Umeå University, Faculty of Science and Technology, Molecular Biology (Faculty of Science and Technology).
2006 (English)In: Molecular Microbiology, ISSN 0950-382X, Vol. 60, no 6, 1520-1533 p.Article in journal (Refereed) Published
Abstract [en]

In this report we have examined the role of the regulatory alarmone (p)ppGpp on expression of virulence determinants of uropathogenic Escherichia coli strains. The ability to form biofilms is shown to be markedly diminished in (p)ppGpp-deficient strains. We present evidence (i) that (p)ppGpp tightly regulates expression of the type 1 fimbriae in both commensal and pathogenic E. coli isolates by increasing the subpopulation of cells that express the type 1 fimbriae; and (ii) that the effect of (p)ppGpp on the number of fimbrial expressing cells can ultimately be traced to its role in transcription of the fimB recombinase gene, whose product mediates inversion of the fim promoter to the productive (ON) orientation. Primer extension analysis suggests that the effect of (p)ppGpp on transcription of fimB occurs by altering the activity of only one of the two fimB promoters. Furthermore, spontaneous mutants with properties characteristic of ppGpp(0) suppressors restore fimB transcription and consequent downstream effects in the absence of (p)ppGpp. Consistently, the rpoB3770 allele also fully restores transcription of fimB in a ppGpp(0) strain and artificially elevated levels of FimB bypass the need for (p)ppGpp for type 1 fimbriation. Our findings suggest that the (p)ppGpp-stimulated expression of type 1 fimbriae may be relevant during the interaction of pathogenic E. coli with the host.

Place, publisher, year, edition, pages
2006. Vol. 60, no 6, 1520-1533 p.
Keyword [en]
Agglutination, Bacterial Proteins/metabolism, Biofilms/growth & development, DNA Nucleotidyltransferases/genetics, DNA-Binding Proteins/*genetics/metabolism, Escherichia coli/drug effects/genetics/*pathogenicity, Escherichia coli Proteins/*genetics/metabolism, Fimbriae Proteins/genetics, Fimbriae; Bacterial/genetics, Gene Expression Regulation; Bacterial, Guanosine Pentaphosphate/genetics/pharmacology/*physiology, Guanosine Tetraphosphate/genetics/pharmacology/*physiology, Integrases/*genetics, Mutation, Promoter Regions (Genetics)/drug effects, Sigma Factor/metabolism, Suppression; Genetic, Transcription; Genetic/drug effects, Urologic Diseases/microbiology, Yeasts/cytology
URN: urn:nbn:se:umu:diva-16638DOI: doi:10.1111/j.1365-2958.2006.05191.xPubMedID: 16796685OAI: diva2:156311
Available from: 2008-01-08 Created: 2008-01-08 Last updated: 2010-03-04Bibliographically approved
In thesis
1. New insights into the role of ppGpp and DksA through their effect on transcriptional regulation of housekeeping and colonization related genes of Escherichia coli
Open this publication in new window or tab >>New insights into the role of ppGpp and DksA through their effect on transcriptional regulation of housekeeping and colonization related genes of Escherichia coli
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacteria have the ability to sense different environmental signals. When an environmental stress is detected, bacteria rapidly adjust their gene expression profile to be able to survive and thrive. The transduction of such environmental signals often requires the coordinated involvement of several factors that constitute complex regulatory networks. Hence, depending on the combination of signals, a unique gene expression profile required to adapt to the specific stress conditions is generated. Proteins are the best-known regulatory factors. However, non-proteinaceous molecules are also important in signal-responsive control of bacterial gene expression. Alarmones are low molecular weight non-proteinaceous regulatory factors which can characteristically be rapidly turned-over to mediate instant changes in gene expression. One such alarmone is the modified nucleotide ppGpp, which directly binds to RNA polymerase to alter its activity. The levels of this alarmone are expected to rapidly increase in response to any environmental stress that result in slow proliferation. DksA, a putative ppGpp co-regulator that likewise directly targets RNA polymerase, has been suggested to be required for both the positive and negative regulation mediated by ppGpp in Escherichia coli.

This thesis describes dissection of the role of ppGpp and DksA on transcriptional regulation, primarily using the fim genetic determinant that encodes for the type 1 fimbriae. Type 1 fimbriae are involved in adhesion to abiotic surface and initial adhesion/invasion of bladder cells, as well as in biofilm formation. We found that ppGpp regulates phase variation by increasing the sub-population of cells that express the fimbriae. The effect of ppGpp was ultimately traced to its role in transcription of the fimB gene that encodes a recombinase involved in the phase variation process (paper 1). In contrast, we unexpectedly found that lack of DksA causes an increase, rather than a decrease, in transcription from the fimB P2 promoter in vivo. However, in vitro transcription studies demonstrated that ppGpp and DksA, both independently and co-dependently, stimulate transcription from the fimB P2 promoter. These seemingly contradictory results from the in vivo and in vitro transcriptional studies were shown to be, at least in part, a consequence of the increased association of Gre-factors with RNA polymerase that can occur in the absence of DksA in vivo (paper 2).

The results outlined above have implications for the role of ppGpp and/or DksA in global gene expression. Using gene expression profile (microarray analysis) during the transition from logarithmic to stationary phase of E. coli, we found that while most of the genes regulated by ppGpp and DksA are regulated in the same direction by the two factors, many were not. In addition to the fim genes, genes involved in flagella functioning, taxis responses, and a few genes encoding different transport systems are also differentially regulated in ppGpp- and DksA-deficient strains in vivo. Our results clearly indicate that the effect of deficiencies in ppGpp and DksA is far more complex than phenotypic similarity of the corresponding mutants anticipated by the proposed concerted action of ppGpp and DksA on gene expression (paper 2 & 3).

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Medicinska fakulteten), 2008. 65 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1184
Escherichia coli, type 1 fimbriae, fimB, phase variation, transcription, global gene regualtion, ppGpp, DksA, gre-factors, RNA polymerase
National Category
Microbiology in the medical area
urn:nbn:se:umu:diva-1669 (URN)978-91-7264-536-3 (ISBN)
Public defence
2008-06-04, Major Groove, 6L, Molekylärbiologen, Umeå, 09:00 (English)
Available from: 2008-05-20 Created: 2008-05-20 Last updated: 2009-05-08Bibliographically approved

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