THE 102-KILOBASE UNSTABLE REGION OF YERSINIA-PESTIS COMPRISES A HIGH-PATHOGENICITY ISLAND LINKED TO A PIGMENTATION SEGMENT WHICH UNDERGOES INTERNAL REARRANGEMENT

Several pathogenicity islands have recently been identified in differe nt bacterial species, including a high-pathogenicity island (HPI) in Y ersinia enterocolitica 1B. In Y. pestis, a 102-kb chromosomal fragment (pgm locus) that carries genes involved in iron acquisition and colon y pigmentation can be deleted en bloc. In this study, characterization and mapping of the 102-kb region of Y. pestis 6/69 were performed to determine if this unstable region is a pathogenicity island. We found that the 102-kb region of I: pestis is composed of two clearly distinc t regions: an approximate to 35-kb iron acquisition segment, which is an HPI per se, linked to an approximate to 68-kb pigmentation segment. This linkage was preserved in all of the Y. pestis strains studied. H owever, several nonpigmented I: pestis strains harboring an irp2 gene have been previously identified, suggesting that the pigmentation segm ent is independently mobile. Comparison of the physical map of the 102 -kb region of these strains with that of strain 6/69 and complementati on experiments were carried out to determine the genetic basis of this phenomenon. We demonstrate that several different mechanisms involvin g mutations and various-size deletions are responsible for the nonpigm ented phenotype in the nine strains studied. However, no deletion corr esponded exactly to the pigmentation segment. The 102-kb region of I: pestis is an evolutionarily stable linkage of an HPI with a pigmentati on segment in a region of the chromosome prone to rearrangement in vit ro.