Molecular biology of the Borrelia, bacteria with linear replicons.

The genus Borrelia was known more than a century ago following the discovery of Borrelia recurrentis as the causative agent of epidemic relapsing fever. Interest in Borrelia increased dramatically after the recent discovery of Lyme disease and the observation that it is caused by a novel member of the genus. Borrelia are spirochaetes, organisms that comprise a separate phylum in the kingdom of eubacteria (Woese, 1987). They differ from other bacteria in having a helical shape with multiple waves and endoflagella which are located between the inner and outer membrane. In this review, we concentrate on the molecular biology of the causative agents of Lyme disease and North American relapsing fever (Borrelia btlrgdorferi senstl lato and Borrelia hermsii, respectively) because they have received the most research attention. To contain the review within reasonable limits we have not attempted to cover the taxonomy of the Borrelia or the widespread literature on antigenic variation of B. hermsii. Interested readers are referred to recent reviews on these topics by Barbour (1990) and Wilske e t al. (1992).