African relapsing fever borreliae genomospecies revealed by comparative genomics

Abstract

Background: Relapsing fever borreliae are vector-borne bacteria responsible for febrile infection in humans in North America, Africa, Asia, and in the Iberian Peninsula in Europe. Relapsing fever borreliae are phylogenetically closely related, yet they differ in pathogenic- ity and vectors.Their long-termtaxonomy, based on geography and vector grouping, needs to be re-apprised in a genomic context.We therefore embarked into genomic analyses of relapsing fever borreliae, focusing on species found in Africa. Results: Genome-wide phylogenetic analyses group OldWorld Borrelia crocidurae, Borre- lia hispanica, B. duttonii, and B. recurrentis in one clade, and NewWorld Borrelia turicatae and Borrelia hermsii in a second clade. Accordingly, average nucleotide identity is 99% among B. duttonii, B. recurrentis, and B. crocidurae and 96% between latter borreliae and B. hispanica while the similarity is 86%between OldWorld and NewWorld borreliae. Com- parative genomics indicates that the OldWorld relapsing fever B. duttonii, B. recurrentis, B. crocidurae, and B. hispanica have a 2,514-gene pan genome and a 933-gene core genome that includes 788 chromosomal and 145 plasmidic genes. Analyzing the role that natural selection has played in the evolution of Old World borreliae species revealed that 55 loci were under positive diversifying selection, including loci coding for membrane, ?agellar, and chemotaxis proteins, three categories associated with adaption to speci?c niches. Conclusion: Genomic analyses led to a reappraisal of the taxonomy of relapsing fever bor-reliae in Africa. These analyses suggest that B. crocidurae, B. duttonii, and B. recurrentis are ecotypes of a unique genomospecies, while B. hispanica is a distinct species.