The Shiga-toxin VT2-encoding bacteriophage φ297 integrates at a distinct position in the Escherichia coli genome

The plaque-forming VT2-encoding lambdoid bacteriophage p297 was isolated from a Belgian clinical Escherichia coli O157:H7 isolate. PCR walking, starting from the int gene of phage phi297, demonstrated that the phi297 prophage integrated in the yecE gene of a lysogenic E. coli K12 strain. This integration site, in E. coli K12 and in the original clinical O157:H7 isolate, was confirmed by PCR using primers flanking this site. The excisionase protein of phage phi297 is identical to the excisionase of VT1-encoding phage VT1-Sakai, while the integrases, which are 82% identical, show significant sequence divergence in the central and C-terminal region. This can explain the different integration sites of both prophages. The activity of the integrase was proven by its ability to mediate the integration of a suicide plasmid, carrying the attachment site of phi297, at the appropriate position in the E. coli chromosome. (C) 2002 Elsevier Science B.V. All rights reserved.