ANALYSIS OF THE DISTRIBUTION AND MOLECULAR HETEROGENEITY OF THE OSPD GENE AMONG THE LYME-DISEASE SPIROCHETES - EVIDENCE FOR LATERAL GENE EXCHANGE

Analysis of the ospD gene has revealed that this gene is not universal among Lyme disease spirochete isolates. The gene was found to be carr ied by 90, 50, and 24% of the Borrelia garinii, B. afzelii, and B. bur gdorferi isolates tested. Size variability in the ospD-encoding plasmi d was also observed. Sequence analysis has demonstrated the presence o f various numbers of a 17-bp repeated sequence in the upstream control (promoter) region of the gene. In addition, a region within the codin g sequence where various insertions, deletions, and direct repeats occ ur was identified. ospD gene sequences from 31 different isolates were determined and utilized in pairwise sequence comparisons and construc tion of a gene tree. These analyses suggest that the ospD gene was the target of several recombinational events and that the gene was recent ly acquired by Lyme disease spirochetes and laterally transferred betw een species.