Trans-Atlantic exchanges have shaped the population structure of the Lyme disease agent Borrelia burgdorferi sensu stricto

S. Castillo-Ramírez, V. Fingerle, S. Jungnick, R. K. Straubinger, S. Krebs, H. Blum, D. M. Meinel, H. Hofmann, P. Guertler, A. Sing, G. Margos
2016 Scientific Reports  
The origin and population structure of Borrelia burgdorferi sensu stricto (s.s.), the agent of Lyme disease, remain obscure. This tick-transmitted bacterial species occurs in both North America and Europe. We sequenced 17 European isolates (representing the most frequently found sequence types in Europe) and compared these with 17 North American strains. We show that trans-Atlantic exchanges have occurred in the evolutionary history of this species and that a European origin of B. burgdorferi
more » ... s. is marginally more likely than a USA origin. The data further suggest that some European human patients may have acquired their infection in North America. We found three distinct genetically differentiated groups: i) the outgroup species Borrelia bissettii, ii) two divergent strains from Europe, and iii) a group composed of strains from both the USA and Europe. Phylogenetic analysis indicated that different genotypes were likely to have been introduced several times into the same area. Our results demonstrate that irrespective of whether B. burgdorferi s.s. originated in Europe or the USA, later trans-Atlantic exchange(s) have occurred and have shaped the population structure of this genospecies. This study clearly shows the utility of next generation sequencing to obtain a better understanding of the phylogeography of this bacterial species. Genome sequencing has drastically changed our understanding of microbial microevolution over the past decades. This is particularly the case for bacteria causing infectious diseases. Furthermore, the advent of next-generation sequencing (NGS) has allowed scientists to handle large population samples and to address a variety of biological questions concerning the evolution and ecology of bacterial pathogens. For example, NGS data has been used to study pathogen evolution within a single patient 1 , transmission chains within a single hospital 2,3 and clonal diversification over time and space 4,5 . Without any doubt the unprecedented resolution provided by NGS is changing the way in which evolutionary biology and molecular epidemiology studies are conducted 4-6 . Borrelia burgdorferi sensu stricto, a tick-borne spirochete bacterium, belongs to the species complex B. burgdorferi sensu lato (s.l.) that now comprises more than 20 accepted and proposed species of which five are regularly isolated from human patients 7,8 . The species that cause Lyme Borreliosis (LB) (also called Lyme disease) include B. burgdorferi s.s., B. afzelii, B. spielmanii, B. garinii and B. bavariensis. LB can be regarded as a multi-systemic disease, because it presents different symptoms in patients, such as erythema migrans (EM), arthritis, neurological manifestations (neuroborreliosis) or lymphocytoma 9-11 . So far, B. burgdorferi s.s. is the only human pathogenic Borrelia species of the Lyme borreliosis group of spirochetes in North America 9 and symptoms described in the USA differ somewhat from those in Europe 11-13 . LB is a zoonotic vector-borne disease, hence, the natural transmission cycles of these bacteria depend on vertebrate reservoir hosts and vector ticks of the Ixodes persulcatus species complex 14,15 . This ecological dependence
doi:10.1038/srep22794 pmid:26955886 pmcid:PMC4783777 fatcat:ipaoyew7qfeqvglj22aiwjouvi