Phylogenetic population structure of F. tularensis subspecies holarctica from the Country of Georgia

Background: Francisella tularensis, the causative agent of tularemia, displays subspecies-specific differences in virulence and geographic distribution. Our phylogenetic understanding of the most geographically dispersed subspecies, holarctica (found throughout the Northern Hemisphere), remains limited because of its significant genetic homogeneity and lack of genetic knowledge of holarctica isolates outside Europe and Northern America. Results: Here we describe the phylogenetic structure of holarctica isolates from the country of Georgia through sequencing the whole-genome of a Georgian strain. The Georgian strains belong to the B.Br.013/014 subclade and descended from a major lineage within the B.Br.013/014 subclade that is distinct and basal to the lineages of the European strains. We identified five phylogenetic groups within the Georgian lineage, reflecting considerable diversity within a small geographic scale. Descendents of the Georgian lineage was found in the Ukraine. Conclusion: We describe the phylogenetic structure of F. tularensis descendents in Georgia. They arose from a newly described distinct lineage within the B.Br.013/014 subclade that separated from the common ancestor before those lineages of the European descendents. The descendents of this newly described lineage are phylogenetically diverse and appear to be concentrated along regions that boarder Europe and Asia.