The bdr gene families of the Lyme disease and relapsing fever spirochetes:Potential influence on biology, pathogenesis, and evolution

Species of the genus Borrelia cause human and animal infections, including Lyme disease, relapsing fever, and epizootic bovine abortion. The borrelial genome is unique among bacterial genomes in that it is composed of a linea r chromosome and a series of linear and circular plasmids. The plasmids exh ibit significant genetic redundancy and carry 175 paralogous gene families, most of unknown function. Homologous alleles on different plasmids could i nfluence the organization and evolution of the Borrelia genome by serving a s foci for interplasmid homologous recombination. The plasmid-carried Borre lia direct repeat (bdr) gene family encodes polymorphic, acidic proteins wi th putative phosphorylation sites and transmembrane domains. These proteins may play regulatory roles in Borrelia. We describe recent progress in the characterization of the Borrelia bdr genes and discuss the possible influen ce of this gene family on the biology, pathogenesis, and evolution of the B orrelia genome.