The high-pathogenicity island of Yersinia enterocolitica Ye8081 undergoes low-frequency deletion but not precise excision, suggesting recent stabilization in the genome

Highly pathogenic strains of Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica are characterized by the possession of a pathogenicity isla nd designated the high-pathogenicity island (HPI). This 35- to 45-kb island carries an iron uptake system named the yersiniabactin locus. While the HP Is of Y. pestis and Y. pseudotuberculosis are subject to high-frequency spo ntaneous deletion from the chromosome,,ve were initially unable to obtain H PI-deleted Y. enterocolitica 1B isolates. In the present study, using a pos itive selection strategy,,ve identified three HPI-deleted mutants of Y. ent erocolitica strain Ye8081. In these three independent clones, the chromosom al deletion aas not limited to the HPI but encompassed a larger DNA fragmen t of approximately 140 kb. Loss of this fragment, which occurred at a frequ ency of approximately 5 x 10(-7), resulted in the disappearance of several phenotypic traits, such as growth in a minimal medium, hydrolysis of o-nitr ophenyl-beta-D-thiogalactopyranoside, Tween esterase activity, and motility , and in a decreased virulence for mice. However, no precise excision of th e Ye8081 HPI was observed. To gain more insight into the molecular basis fo r this phenomenon, the putative machinery of HPI excision in Y. enterocolit ica was analyzed and compared to that in Y. pseudotuberculosis. We show tha t the probable reasons for failure of precise excision of the HPI of Y. ent erocolitica Ye8081 are (i) the interruption of the P4-like integrase gene l ocated close to its right-hand boundary by a premature stop codon and (ii) lack of conservation of 17-bp att-like sequences at both extremities of the HPI. These mutations may represent a process of HPI stabilization in the s pecies Y. enterocolitica.