Fig. 6.

Model for the evolution of vlp- and vsp-related genes in Borrelia. It is hypothesized that a common ancestor of LB and RF organisms contained single copies of primordial vlp and vsp homologues. Following the divergence of LB and RF groups, these precursor genes duplicated and developed into the vls system and ospC in a primordial LB organism, and into the VMP system and vtp in a primordial RF ancestor. Each of these antigenic variation systems and related surface proteins continued to evolve and diverge under the pressure of immune selection.