Borrelia evolutionary genomics

Our research interests in the genus Borrelia are to determine the molecular evolution and adaptation of spirochetes to their host environments, particularly to their tick hosts. We have found a lack of congruence between the molecular phylogenies of the several, diverse tick species and their associated spirochetes, and inferred that shifts in vector preference may be common in borreliae. Specificity of Borrelia for their tick hosts is likely to derive from complex phenotypic differences in the spirochete (as well as the tick) pertaining to the adherence and invasion of tick midgut tissues. The genotypic determinants of these traits are largely unknown, but the extensive family of genes encoding surface molecules, located on linear and circular plasmids, may be particularly relevant in this regard. These plasmidborne genes play an important role in the remarkable adaptation by which borreliae evade the vertebrate immune system. A current research priority in our laboratory is to determine molecular basis of generating and maintaining allelic variation among the genes encoded in the plasmid genomes.

Borrelia burgdorferi population dynamics

In addition to genomic studies, we are currently pursuing micro-evolutionary studies of natural populations of Borrelia burgdorferi and its hosts. To this end, we are evaluating genetic variation within and between several populations of ticks, mice and Borrelia located on a series of small, Lyme disease-endemic, islands off the coast of New England. The faunal composition and profound isolation of these islands make them highly suitable “natural experiments” for studying the pathogen's interactions with the hosts in which it is maintained and transmitted. We seek to determine whether, (1) genetic exchange occurs between lineages of B. burgdorferi in endemic sites; (2) there is a non-random association between mouse-tick-Borrelia genotypes, (3) natural selection maintains allelic diversity among Borrelia antigenic determinants. The use of islands as natural experiments and analysis of all trophic levels in the complex disease cycle is novel and make this a highly innovative approach for understanding parasite-host population dynamics.