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Infect Immun, April 1998, p. 1735-1739, Vol. 66, No. 4
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Molecular Characterization of the Fragilysin Pathogenicity Islet of Enterotoxigenic Bacteroides fragilis

J. Scott Moncrief,* A. Jane Duncan, Rhonda L. Wright, Lisa A. Barroso, and Tracy D. Wilkins

Department of Biochemistry, Fralin Center for Biotechnology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0346

Received 22 October 1997/Returned for modification 21 November 1997/Accepted 3 January 1998

Enterotoxigenic strains of Bacteroides fragilis produce an extracellular metalloprotease toxin (termed fragilysin) which is cytopathic to intestinal epithelial cells and induces fluid secretion and tissue damage in ligated intestinal loops. We report here that the fragilysin gene is contained within a small genetic element termed the fragilysin pathogenicity islet. The pathogenicity islet of B. fragilis VPI 13784 was defined as 6,033 bp in length and contained nearly perfect 12-bp direct repeats near its ends. Sequencing across the ends of the pathogenicity islet from two additional enterotoxigenic strains, along with PCR analysis of 20 additional enterotoxigenic strains, revealed that the islet is inserted at a specific site on the B. fragilis chromosome. The site of integration in three nontoxigenic strains contained a 17-bp GC-rich sequence which was not present in toxigenic strains and may represent a target sequence for chromosomal integration. In addition to the fragilysin gene, we identified an open reading frame encoding a predicted protein with a size and structural features similar to those of fragilysin. The deduced amino acid sequence was 28.5% identical and 56.3% similar to fragilysin and contained a nearly identical zinc-binding motif and methionine-turn region.

* Corresponding author. Mailing address: Department of Biochemistry, Fralin Center for Biotechnology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0346. Phone: (540) 231-5094. Fax: (540) 231-7126. E-mail: jmoncrie{at}vt.edu.




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