Plasmid contains unique Helicobacter Pylori insertion sequence IS605

Helicobacter pylori is a human gastric pathogen that causes chronic gastritis, peptic ulcer disease and gastric adenocarcinoma. Other pathogenic bacteria, including Salmonella and Escherichia, contain stretches of sequence that encode pathogenicity genes, and are referred to as pathogenicity islands (PAI); a 40 kbp chromosomal PAI occurs in pathogenic strains of H. pylori. IS605, an insertion sequence unique to H. pylori is found in the PAI of some isolates and is thought to be involved in the deletion formations that are noted in these strains.

Plasmids have been speculated to be responsible, in part, for the rearrangements of the H. pylori PAI. In this study, we describe a 13 kbp plasmid, pHPM186, which contains two copies of IS605. In addition, pHPM186 carries 1.6 kbp of DNA that show strong sequence identity to region 86 of the H. pylori chromosome, which encodes a PARA protein and 2 hypothetical proteins of unknown functions. Also pHPM 186 has a replication gene (repA) with strong sequence identity to repA genes found in pHPM180, pHPM179 and pHel. The sequence analysis of pHPM186 provided direct evidence that portions of the H. pylori chromosome can be carried by plasmids, making these plasmids possible vehicles for movement of chromosomal DNA between H. pylori strains.

Creation of a shuttle vector between H. pylori and E. coli was also attempted in this study. Ligations of the repA region of pHPM186 and a kanamycin resistance gene were transformed into both E. coli and H. pylori. Transformants were recovered only when F$\backslash sp+$ strains of E. coli were used as recipients. Two different sizes of recombinants were isolated that were resistant to kanamycin, but in both the repA region was rearranged. Small H. pylori transformants were initially recovered, but they failed to grow. Attempts to create a shuttle vector showed that the repA gene from H. pylori is not maintained in E. coli, it appears to undergo vast rearrangement. These results provide evidence that a creation of a shuttle vector between this two strains is not possible using this type of recombinant construct.