The bundle-forming pili of enteropathogenic Escherichia coli: transcriptional regulation by environmental signals

Authors

  • Jose Luis Puente,

    1. Department of Microbiology and Immunology Division of Infectious Diseases and Geographic Medicine
    2. Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, 94305, USA.
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    • Instituto De Biotechnologia, Universidad Nacional Autonoma de Mexico APDO, 510–3 Cuerna-vaca, Mor. 62271, Mexico.

    • §

      These authors contributed equally to this study.

  • David Bieber,

    1. Department of Microbiology and Immunology Division of Infectious Diseases and Geographic Medicine
    2. Department of Medicine Division of Infectious Diseases and Geographic Medicine
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    • §

      These authors contributed equally to this study.

  • Sandra W. Ramer,

    1. Department of Microbiology and Immunology Division of Infectious Diseases and Geographic Medicine
    2. Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, 94305, USA.
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  • William Murray,

    1. Department of Microbiology and Immunology Division of Infectious Diseases and Geographic Medicine
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    • Biological Sciences Department, San Jose State University, San Jose, California 95192, USA.

  • Gary K. Schoolnik

    Corresponding author
    1. Department of Microbiology and Immunology Division of Infectious Diseases and Geographic Medicine
    2. Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, 94305, USA.
    3. Department of Medicine Division of Infectious Diseases and Geographic Medicine
    • *For correspondence. E-mail ml.gks.forsythe.stanford.edu; Tel. (414) 7238158; Fax (415) 7231399.

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Summary

The bundle-forming pili (BFP) of enteropathogenic Escherichia coli (EPEC) are required for the development of circumscribed colonies of bacteria attached to the surfaces of cultured epithelial cells, a process termed the localized adherence (LA) phenotype. Similar lesions are evident in jejunal biopsies from EPEC-infected children. BFP production is not constitutive, but instead occurs upon transfer of bacteria from nutrient broth to tissue culture media, indicating that the expression of BFP may be environmentally regulated. To learn more about how BFP protein expression is induced during epithelial-cell adherence, bfpA-cat transcriptional fusions and northern blot analyses were employed to monitor bfpA expression as a function of environmental signals and growth kinetics. bfpA expression was found to be regulated at the transcriptional level, and to require a separate locus on the EPEC adherence factor (EAF) plasmid. Expression occurred selectively during exponential-growth phase and was greatest between 35 and 37°C, and in the presence of calcium. Ammonium (20 mM) significantly reduced bfpA mRNA and protein expression and the development of the LA phenotype. Analysis of the bfpA upstream sequence and identification of the transcription initiation site revealed a conventional σ70-dependent promoter and an AT-rich tract that might affect promoter activity. Taken together, these findings further support the pathogenic role of BFP

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