MLST of housekeeping genes captures geographic population structure and suggests a European origin ofBorrelia burgdorferi

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Abstract
Lyme borreliosis, caused by the tick-borne bacteriumBorrelia burgdorferi, has become the most common vector-borne disease in North America over the last three decades. To understand the dynamics of the epizootic spread and to predict the evolutionary trajectories ofB. burgdorferi, accurate information on the population structure and the evolutionary relationships of the pathogen is crucial. We, therefore, developed a multilocus sequence typing (MLST) scheme forB. burgdorferibased on eight chromosomal housekeeping genes. We validated the MLST scheme onB. burgdorferispecimens from North America and Europe, comprising both cultured isolates and infected ticks. These data were compared with sequences for the commonly used genetic markersrrs-rrlAintergenic spacer (IGS) and the gene encoding the outer surface protein C (ospC). The study demonstrates that the concatenated sequences of the housekeeping genes ofB. burgdorferiprovide highly resolved phylogenetic signals and that the housekeeping genes evolve differently compared with the IGS locus andospC. Using sequence data, the study reveals that North American and European populations ofB. burgdorfericorrespond to genetically distinct populations. Importantly, the MLST data suggest thatB. burgdorferioriginated in Europe rather than in North America as proposed previously.