Genetic analysis of Borrelia.

DNA homology studies were performed on Borrelia hermsii, B. duttoni, B. crocidurae and the O. coriaceus spirochete. These organisms had a genus level relationship with each other. B. hermsii was 17 to 53% homologous with B. duttoni, B. crocidurae, and the O. coriaceus spirochetes; B. crocidurae was 17-32% related to B. hermsii, B. anserina and the O. coriaceus spirochete, and the O. coriaceus spirochete was 28-50% related to B. hermsii, B. crocidurae and B. anserina. The O. coriaceus spirochete was 10% homologous with B. burgdorferi, the etiologic agent of Lyme disease. Plasmid DNA was detected in these strains of Borrelia. Southern blot analysis of plasmid DNA from these strains suggested little or no homology with plasmid DNA from B. hermsii used as a probe. A plasmid of 9.2 kilobases was seen in B. burgdorferi strain CT1. This plasmid was shown to be a tandem repeat with unit length of 4.6 kilobases. Sequences corresponding to this plasmid were detected in several fresh tick isolates from North America, and were not seen in any animal, human or European isolates surveyed. The role in the biology of the spirochete played by this plasmid is unknown.