Abstract
BackgroundThe Borrelia burgdorferi sensu lato (s.l.) species complex consists of tick-transmitted bacteria and currently comprises approximately 20 named and proposed genospecies some of which are known to cause Lyme Borreliosis. Species have been defined via genetic distances and ecological niches they occupy. Understanding the evolutionary relationship of species of the complex is fundamental to explaining patterns of speciation. This in turn forms a crucial basis to frame testable hypotheses concerning the underlying processes including host and vector adaptations.ResultsIllumina Technology was used to obtain genome-wide sequence data for 93 strains of 14 named genospecies of the B. burgdorferi species complex and genomic data already published for 18 additional strain (including one new species) was added. Phylogenetic reconstruction based on 114 orthologous single copy genes shows that the genospecies represent clearly distinguishable taxa with recent and still ongoing speciation events apparent in Europe and Asia. The position of Borrelia species in the phylogeny is consistent with host associations constituting a major driver for speciation. Interestingly, the data also demonstrate that vector associations are an additional driver for diversification in this tick-borne species complex. This is particularly obvious in B. bavariensis, a rodent adapted species that has diverged from the bird-associated B. garinii most likely in Asia. It now consists of two populations one of which most probably invaded Europe following adaptation to a new vector (Ixodes ricinus) and currently expands its distribution range.ConclusionsThe results imply that genotypes/species with novel properties regarding host or vector associations have evolved recurrently during the history of the species complex and may emerge at any time. We suggest that the finding of vector associations as a driver for diversification may be a general pattern for tick-borne pathogens. The core genome analysis presented here provides an important source for investigations of the underlying mechanisms of speciation in tick-borne pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3016-4) contains supplementary material, which is available to authorized users.
Highlights
The Borrelia burgdorferi sensu lato (s.l.) species complex consists of tick-transmitted bacteria and currently comprises approximately 20 named and proposed genospecies some of which are known to cause Lyme Borreliosis
The aim of our study was to produce a robust phylogeny for the B. burgdorferi s.l. species complex to obtain a better understanding of their global evolution and to put into perspective the evolution of host and vector adaptations
To gain knowledge on the global evolution of the bacterial species complex B. burgdorferi s.l., we sequenced 93 strains belonging to 14 of the approximately 20 described genospecies of the complex (Additional file 1: S1) and downloaded chromosome sequence data for 18 additional Lyme Borreliosis (LB) strains including one strain of B. chilensis [23] and for the Relapsing Fever strain Ly of B. duttonii that was used as outgroup in the phylogeny [24]
Summary
The Borrelia burgdorferi sensu lato (s.l.) species complex consists of tick-transmitted bacteria and currently comprises approximately 20 named and proposed genospecies some of which are known to cause Lyme Borreliosis. Phylogenetic analysis is a powerful tool for generating hypotheses on the pattern of descent and evolution of species and strains, their host and vector adaptation or pathogenicity. This in turn provides information for comparative genomics, an effective approach for studying genetic differences between strains and/or species that may lead to differences in phenotype related to host or vector associations, pathogenicity and others [1, 2]. In this study we used vector-borne bacterial pathogens, the Borrelia burgdorferi sensu lato (s.l.) species complex, to advance the understanding of the phylogenetic relationship of members of this species complex and to put into perspective the evolution of vector- and host associations. Host and vector associations are obviously contributing to the asymmetrical geographic distribution of species within the distribution range between around 40th and 60th degree northern latitude but the question of how these traits evolved has remained unresolved
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
