EXPANDED DIVERSITY AMONG CALIFORNIAN BORRELIA ISOLATES AND DESCRIPTION OF BORRELIA-BISSETTII SP. NOV. (FORMERLY BORRELIA GROUP DN127)

Up to now, the only species in the complex Borrelia burgdorferi sensu late known to cause Lyme borreliosis in the United States has been B. burgdorferi sensu stricto. However, some atypical strains closely rela ted to the previously designated genomic group DN127 have been isolate d in the United States, mostly in California. To explore the diversity of B. burgdorferi sensu late group DN127, we analyzed the nucleotide sequences of the rrf-rrl intergenic spacer regions from 19 atypical st rains (18 from California and one from New York) and 13 North American B, burgdorferi sensu stricto strains (6 from California). The spacer region sequences from the entire B, burgdorferi sensu late complex ava ilable in data banks were used for comparison, Phylogenetic analysis o f sequences shows that the main species of the B. burgdorferi sensu la te complex (B. afzelii, B, garinii, B. andersonii, B. japonica, B. bur gdorferi sensu stricto, B, valaisiana, and B, lusitaniae) each form a coherent cluster, A heterogeneous group comprising strains belonging t o the previously designated group DN127 clustered separately from B. b urgdorferi sensu stricto, Within this cluster, the deep branches expre ssing the distances between the rrf-rrl sequences reflect a high level of divergence. This unexpected diversity contrasts with the monomorph ism exhibited by B. burgdorferi sensu stricto, To clarify the taxonomi c status of this highly heterogeneous group, analysis of the rrs seque nces of selected strains chosen from deeply separated branches was per formed. The results show that these strains significantly diverge at a level that is compatible,vith several distinct genomic groups. We con clude that the taxonomy and phylogeny of North American B. burgdorferi sensu late should be reevaluated. For now, we propose that the genomi c group DN127 should be referred to as a new species, B, bissettii sp, nov., and that other related but distinct strains, which require furt her characterization, be referred to as Borrelia spp.