We propose to investigate the genetic regulation and pathobiologic significance of fimbrial phase variation in Escherichia coli. All strains of E. coli examined to date, including laboratory and clinical isolates, have preserved the ability to express type 1 fimbriae, which are adhesive organelles that promote bacterial adherence to mucosal surfaces. These organelles are probably important in permitting E. coli to colonize and infect humans, particularly in the genitourinary and gastrointestinal tracts. But type 1 fimbriae also mediate bacterial binding to human phagocytic cells, which also contain the mannose receptors specific for type 1 fimbriae. Thus, at invasive phases of infection, fimbriae might actually be suicide factors for the bacteria. Presumably to overcome this need for expressing and then shedding fimbriae, bacteria have evolved a system of phase variation that turns the fimbriae expression on and off. We demonstrated that phase variation is regulated genetically by an invertible element of DNA, whose oscillating orientation correlates with the on-off transcription of the fimbrial subunit gene. Also, at least two trans-active elements were discovered that are required to promote the DNA rearrangement. We propose two major aims: 1. Characterize the molecular details of phase variation by examining both the cis-active switch and the trans-active factors. A variety of molecular genetic and biochemical approaches will be attempted. 2. Determine the role of phase variation in bacterial physiology and pathobiology. To this and phase-locked mutants will be constructed. A minor aim is to continue the investigation of the biology of organelle assembly using immunoelectron microscopy. Eventually the investigators hope to develop a detailed understanding of the molecular mechanisms and cell biologic significance of E. coli phase variation.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Bacteriology and Mycology Subcommittee 1 (BM)
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University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
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Blomfield, I C; Kulasekara, D H; Eisenstein, B I (1997) Integration host factor stimulates both FimB- and FimE-mediated site-specific DNA inversion that controls phase variation of type 1 fimbriae expression in Escherichia coli. Mol Microbiol 23:705-17
McClain, M S; Blomfield, I C; Eberhardt, K J et al. (1993) Inversion-independent phase variation of type 1 fimbriae in Escherichia coli. J Bacteriol 175:4335-44
Blomfield, I C; Calie, P J; Eberhardt, K J et al. (1993) Lrp stimulates phase variation of type 1 fimbriation in Escherichia coli K-12. J Bacteriol 175:27-36
Gally, D L; Bogan, J A; Eisenstein, B I et al. (1993) Environmental regulation of the fim switch controlling type 1 fimbrial phase variation in Escherichia coli K-12: effects of temperature and media. J Bacteriol 175:6186-93
McClain, M S; Blomfield, I C; Eisenstein, B I (1991) Roles of fimB and fimE in site-specific DNA inversion associated with phase variation of type 1 fimbriae in Escherichia coli. J Bacteriol 173:5308-14
Blomfield, I C; McClain, M S; Princ, J A et al. (1991) Type 1 fimbriation and fimE mutants of Escherichia coli K-12. J Bacteriol 173:5298-307
Blomfield, I C; Vaughn, V; Rest, R F et al. (1991) Allelic exchange in Escherichia coli using the Bacillus subtilis sacB gene and a temperature-sensitive pSC101 replicon. Mol Microbiol 5:1447-57
Blomfield, I C; McClain, M S; Eisenstein, B I (1991) Type 1 fimbriae mutants of Escherichia coli K12: characterization of recognized afimbriate strains and construction of new fim deletion mutants. Mol Microbiol 5:1439-45
Eisenstein, B I (1990) New molecular techniques for microbial epidemiology and the diagnosis of infectious diseases. J Infect Dis 161:595-602
Eisenstein, B I (1990) The polymerase chain reaction. A new method of using molecular genetics for medical diagnosis. N Engl J Med 322:178-83

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