EVIDENCE OF PAST RECOMBINATION EVENTS AMONG THE GENES ENCODING THE ERP ANTIGENS OF BORRELIA-BURGDORFERI

A single Borrelia burgdorferi bacterium may contain six or more differ ent 32 kb circular plasmids (cp32s). Although these plasmids are homol ogous throughout much of their sequences, two loci have been identifie d at which they can vary significantly. The cp32 plasmids and their re latives each contain two adjacent genes, orfC and orf3, that vary in s equence between plasmids found within clones of individual bacteria. T he orfC gene product is homologous to proteins involved in partitionin g of bacterial plasmids. and the differences at this locus between pla smids may account for their compatibility. The orfC-orf3 loci are loca ted approximately 5 kb from another variable locus called erp. The orf C-orf3 loci were used as physically linked markers to assess genetic r earrangements in the erp loci; this revealed examples of recombination involving both individual genes and entire erp loci. Recombination of the genes encoding the ErP antigens might contribute to the evasion o f the mammalian immune response and could play roles in the establishm ent and persistence of B. burgdorferi infections in mammalian hosts.