Genetic Diversity of Siberian Isolates of Borrelia burgdorferi Sensu Lato by the ospA Gene

The genetic diversity of the <i>osp</i>A gene of the <i>Borrelia burgdorferi</i> sensu lato species complex encoding outer surface protein A has been widely investigated. However, the information on the genetic variability of <i>Borrelia</i> isolates from Siberia for this gene is limited. In this study, we analyzed complete <i>osp</i>A gene sequences from 36 <i>Borrelia</i> isolates from Western Siberia, comprising 6 <i>Borrelia afzelii</i>, 16 <i>Borrelia bavariensis</i>, 1 <i>Borrelia garinii</i>, and 13 "<i>Candidatus</i> Borrelia sibirica" isolates. The obtained <i>osp</i>A gene sequences of <i>B. afzelii</i> were conserved and formed a single clade. In contrast, <i>B. bavariensis</i> sequences were highly variable, segregating into two distinct clades consistent with the phylogeography of Asian isolates. Notably, the <i>B. bavariensis</i> samples identified in molted <i>Ixodes trianguliceps</i> and <i>Ixodes apronophorus</i> were first characterized for the <i>osp</i>A gene; the obtained sequences corresponded to those from <i>I. persulcatus</i>. This study provides the first characterization of the <i>osp</i>A gene in "<i>Candidatus</i> B. sibirica", revealing highly conserved sequences (99.8-100% intraspecific identity). The <i>osp</i>A gene sequences of "<i>Candidatus</i> B. sibirica" shared less than 88.7% identity with those of other <i>Borrelia</i> genospecies. Phylogenetic analysis placed "<i>Candidatus</i> B. sibirica" in a unique, well-supported clade, confirming its distinct phylogenetic status and suggesting potential ecological specialization in nidicolous <i>Ixodes</i> species.