Phylogenesis of Relapsing Fever Borrelia spp.

This study analyzed the phylogenetic relationships of 20 relapsing fever (RF) Borrelia species by sequencing and comparing their 16S ribosomal RNA (rrs) genes. Complete rrs sequences were aligned and examined using three phylogenetic methods: neighbor-joining, maximum-parsimony, and maximum-likelihood. Sequence similarity among RF Borrelia species ranged from 97.7 to 99.9%. The analysis divided RF Borrelia into three major phylogenetic clusters: one containing B. crocidurae, B. duttonii, B. recurrentis, and B. hispanica; another with B. coriaceae, B. lonestari, B. miyamotoi, B. parkeri, B. turicatae, and B. hermsii; and a third containing only B. anserina. The phylogenetic position of B. persica remained uncertain. To address the difficulty of culturing these fastidious organisms, the authors designed RF Borrelia-specific primers and demonstrated that restriction fragment length polymorphism (RFLP) analysis of PCR-amplified rrs genes could reliably distinguish between RF Borrelia species, offering a practical diagnostic tool.

Key findings

• Phylogenetic analysis of 16S rRNA sequences divided 20 relapsing fever Borrelia species into three major evolutionary clusters with distinct relationships.
• Sequence similarity among RF Borrelia species ranged from 97.7 to 99.9%, suggesting the current taxonomy should be revised.
• PCR amplification combined with restriction fragment length polymorphism (RFLP) analysis provides a rapid, culture-independent method for identifying and distinguishing RF Borrelia species.
• B. recurrentis may represent a clone from the B. crocidurae-B. duttonii-B. hispanica cluster that adapted to human lice vectors rather than being a separate species.
• B. anserina appears evolutionarily distinct from other RF Borrelia species, possibly reflecting ancient adaptation to migratory birds.