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Lyme borreliosis, also known as
Lyme disease, is now the most common vector transmitted
disease in the northern hemisphere. It is caused by the spirochete Borrelia burgdorferi and related species. In addition to their clinical importance, these organisms are fascinating to study because of the wide variety of unusual features they possess. Ongoing work in the laboratory in several areas will be described. (1) The segmented genomes contain up to two dozen genetic elements, the majority of which are linear with covalently closed hairpin ends. These linear DNAs also display a very high degree of ongoing genetic rearrangement. Mechanisms for these processes will be described. (2) Persistent infection by Borrelia species requires antigenic variation through a complex DNA rearrangement process at the vlsE locus on the linear plasmid lp28-1. Novel features of this recombination process will be presented. (3) Evidence for a new global regulatory pathway of B. burgdorferi gene expression that is required for pathogenicity will be described. The DEAH box RNA helicase HrpA is involved in this pathway, which may be relevant in other bacteria. (4) The mechanism of B. burgdorferi to effectively disseminate throughout its host is being studied in real time by high resolution intravital imaging in live mice. Recent work will be presented.