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. 1998 Apr;66(4):1735-9.
doi: 10.1128/IAI.66.4.1735-1739.1998.

Molecular characterization of the fragilysin pathogenicity islet of enterotoxigenic Bacteroides fragilis

J S Moncrief  1 , A J Duncan, R L Wright, L A Barroso, T D Wilkins
Affiliations

Molecular characterization of the fragilysin pathogenicity islet of enterotoxigenic Bacteroides fragilis

J S Moncrief et al. Infect Immun. 1998 Apr.

Abstract

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.

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Figures

FIG. 1
FIG. 1
Schematic of the fragilysin pathogenicity islet. ORFs are represented by thick arrows. Small arrows at the ends represent direct repeats. Open boxes at the ends represent DNA outside the islet, which is also present in nontoxigenic B. fragilis. Restriction sites are BamHI (B), EcoRI (E), PstI (P), SacI (Sc), SmaI (Sm), XmnI (X), HindIII (H), and NdeI (N).
FIG. 2
FIG. 2
Nucleotide sequences used to define the ends of the fragilysin pathogenicity islet. The nontoxigenic sequence was from B. fragilis VPI 2553. Toxigenic sequences across the left and right ends of the pathogenicity islet were from enterotoxigenic B. fragilis strain VPI 13784. Lowercase letters represent where the sequence from the nontoxigenic strain varied from the sequence flanking the ends of the islet. A 17-bp sequence present only in DNA from the nontoxigenic strain is boxed. Arrows indicate the ends of the islet and corresponding nucleotide number. Direct repeats (DR) are underlined.
FIG. 3
FIG. 3
Alignment of the predicted amino acid sequences of MP II and fragilysin. |, identical residues; *, conserved substitutions.
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