Dr Ian Blomfield
Senior Lecturer in Molecular Microbiology
School of Biosciences
- 01227 (82)3697
Dr Ian Blomfield joined the School of Biosciences in April 1999. He is a member of the Microbial Pathogenesis Group and the Centre for Biomedical Informatics. Work in the Blomfield group is focused on understanding how and why genes expression is controlled in bacteria, with an emphasis on virulence factors in E.coli.back to top
Also view these in the Kent Academic Repository
back to top
Phase variation in E.coli
The expression of many cell surface virulence factors in bacteria are controlled by phase variation. Work in the infectious diseases group is focused on understanding the phase variation in expression of the type 1 fimbrial adhesin (fim) in E.coli.
Type 1 fimbriae are a virulence factor in uropathogenic E.coli that cause cystitis (Bladder infection), yet are also produces by many commensal strains. Phase variation is controlled by the site-specific inversion of a short (314bp) DNA element (the fim switch) that contains the promoter for the fimbrial structural genes. Work in the laboratory is focused on understanding how and why the fim switch is regulated. Understanding the fim system could lead eventually to new approaches for treating and managing infections.
More about phase variation and fim
The gene required for the expression of type 1 fimbriae in E.coli are organised into a cluster on the genome (Fig 1). Phase variation (ON↔OFF switching of gene expression) controls many bacterial virulence factors. For type 1 fimbriation in E.coli (fim), phase variation operates at the level of transcription, and involves the inversion of a short (~300 bp) DNA element (fimS). The fim inversion requires one of two recombinases, FimB or FimE. Whereas FimE dominates ON-to-OFF recombination, inversion of the fim "switch" from OFF-to-ON is catalyzed mainly by FimB. Both recombinase specificity, and suppression of recombinase expression in the OFF orientation ("Orientational control"), contribute to the specificity of the fimE locus. Inversion of the fim switch is affected by a number of co-factors, including Lrp (Leucine-responsive regulatory protein) , IHF (Integration host factor) and H-NS, and is regulated in response to environmental factors including sialic acid and N-acetylglucosamine, the branched-chain amino acids (isoleucine, valine, and leucine) and alanine and temperature. We propose that type 1 fimbriation is regulated in response to inflammatory indicators in the host and that this helps the bacterium circumvent host defences.3
Fig. 1. Organisation of the fim region in phase ON cells. The fim genes are situated at 98 minutes on the E.coli K-12 genome, with transcription of all of the genes in a clockwise direction (arrows). fimB is separated from the divergently transcribed nanC operon by a large intergenic region or "grey hole". NanC is a sialic acid porin,4 and the expression of ths gene and fimB are coordinated by shaired regulatory elements.3-5 The fim invertible element or "switch", only 314bp in length, lies downstream of fimE, and contains a promoter that drives transcription of the fim structural genes in the ON orientation. Whereas fimA encodes the major subunit, fimH encodes the mannose-binding adhesin.
Type 1 fimbriae are a virulence factor in urinary tract infections, and understanding how and why the expression of the adhesin is regulated could lead to new approaches to managing and treating chronic-recurrent cystitis among others.
- Blomfield, I.C., and van der Woude, M. 2002. Regulation and function of phase variation in Escherichia coli in Bacterial Adhesion to Host Tissues (Cambridge University Press). Advances in Molecular and Cellular Microbiology 1: 89-113. [Chapter
- Blomfield, I.C. 2001. The regulation of Pap and type 1 fimbriation in Escherichia coli Advances in Microbial Physiology 45:1-49. [Abstract]
- Sohanpal, B.K., El-Labany, S., Lahooti, M., Plumbridge, J.A., and Blomfield, I.C. 2004. Integrated regulatory responses of fimB to N-acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12. 2004. Proceedings of the National Academy of Sciences U S A. 101:16322-16327. [Abstract] [Full paper]
- Condemine, G., Berrier, C., Plumbridge, J., and Ghazi, A. 2005. Function and expression of an N-acetylneuraminic acid-inducible outer membrane channel in Escherichia coli. Journal of Bacteriology 187:1959-1965. [Abstract] [Full paper]
- Sohanpal, B.K., Friar, S., Roobol, J., Plumbridge, J.A., and Blomfield, I.C. 2007. Multiple co-regulatory elements and IHF are necessary for the control of fimB expression in response to sialic acid and N-acetylglucosamine in Escherichia coli K-12. Molecular Microbiology. 63:1223-1236. [Abstract]
The coordinate control of fimB and the nanC operon
fimB is separated from the divergently transcribed nanC yjhTS operon by a large (1.4kbp) intergenic region (Fig. 1), yet expression of fimB and the nanC operon are co-ordinately controlled by sialic acid-responsive and GlcNAc-responsive regulatory factors NanR and NagC + IHF.3-5 NanC is a sialic acid porin (4) and its co-regulation with fimB expression indicates a connection between sialic acid and adherence that remains to be understood.
The operator site for NanR (ONR), and one of the operator sites for NagC (ONC1),
lie adjacent to Dam methylation sites (GATCNanR and GATCNagC) that are frequently
unmethylated, indicating their inclusion in stable nucleoprotein complexes.
Methylation protection of GATCNanR and GATCNagC requires NanR and NagC
respectively, and is apparently alternate, suggesting that the two proteins
activate fimB expression as part of a regulatory cycle. NanR and NagC are
inactivated by sialic acid and GlcNAc-6P respectively. Since sialic metabolism
generates GlcNAc-6P, inhibition of fimB expression by sialic acid arises by loss
of both NanR and NagC activation. Furthermore the operator sites for NanR and
NagC overlap the nanC operon promoter, and hence expression of these genes and
fimB are coordinated.
Type 1 fimbriae are pro-inflammatory and a virulence factor. For example, the
adhesin both facilitates invasion of, and growth within, host cells as a key step
in uropathogenesis. We proposed that decreased expression of type 1 fimbriation
in the presence of sialic acid and GlcNAc, febrile temperatures and limitation
for the branched-chain amino acids, are all responses that help E.coli to avoid
host defences.1-3,6 Work in our laboratory is focused currently on understanding
how and why NagC and NanR and other factors control type 1 fimbriation as they
do. In addition, we are interested in the function of the nanC yjhTS operon, and
in the toxicity of sialic acid and its metabolic products in E.coli.
- El-Labany, S., Sohanpal, B.K., Lahooti, M., Akerman, R., and Blomfield, I.C. 2003. Distant cis-active sequences and sialic acid control the expression of fimB in Escherichia coli K-12. Molecular Microbiology 49:1109-1118
- Sohanpal, B.K., El-Labany, S., Lahooti, M., Plumbridge, J.A., and Blomfield, I.C. 2004. Integrated regulatory responses of fimB to N-acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12. 2004. Proceedings of the National Academy of Sciences U S A. 101:16322-16327
- Sohanpal, B.K., Friar, S., Roobol, J., Plumbridge, J.A., and Blomfield, I.C. 2007. Multiple co-regulatory elements and IHF are necessary for the control of fimB expression in response to sialic acid and N-acetylglucosamine in Escherichia coli K-12. Molecular Microbiology. 63:1223-1236
- Condemine, G., Berrier, C., Plumbridge, J., and Ghazi, A. 2005. Function and expression of an N-acetylneuraminic acid-inducible outer membrane channel in Escherichia coli. Journal of Bacteriology 187:1959-1965
- Severi, E., Muller, A., Potts, J.R., Leech, A., Williamson, D., Wilson, K.S., and Thomas, G.D. 2007. Sialic acid mutarotation is catalysed by the Escherichia coli beta -propeller protein YJHT. Journal of Biological Chemistry E pub ahead of print
- Lahooti, M., Roesch, P.L., and Blomfield, I.C. 2005. Modulation of the sensitivity of FimB recombination to branched-chain amino acids and alanine in Escherichia coli K-12. Joural of Bacteriology. 187:6273-6280
- Chu, D., Roobol, J., and Blomfield, I.C. 2008. A theoretical interpretation of the transient sialic acid toxicity of a nanR mutant of Escherichia coli. Journal of Molecular Biology. 375:875-889
back to top
Funding from: Wellcome Trust
- BI501 - Gene Expression and Its Control
- BI505 - Infection and Immunity
- BI511 - Physiology of the Microbial Cell I (Module convenor)
- BI601 - Skills for Biochemists
- BI606 - Pathogens & Pathogenicity
- BI635 - Physiology of Microorganisms Plants & Animals (Module convenor)
- BI651 - Skills for Biologists III