Borrelia burgdorferi is a Gram negative bacterium of the Spirocaetaceae family.  As a spirochete, B. burgdorferi is composed of an inner protoplasmic layer, followed by a cell membrane, 7-11 periplasmic flagella, and an outer membrane composed largely of lipids and proteins (Diterich and Hartung, 2001). B. burgdorferi achieves cork-screw motility through the use of axial endoflagella (http://textbookofbacteriology.net/Lyme.html).  The DNA of B. burgdorferi is a 1.5 Mbp genome, a 950 Kbp linear chromosome, 9 linear plasmids, and 12 circular plasmids (Steere, 2001). 

The outer membrane of B. burgdorferi is covered with a series of about 30 proteins called outer surface proteins (Osp).  OspA through OspF have been characterized so far in B. burgdorferi, and OspA and OspB are the most abundant on the spirochete surface.  The Osp and other unique surface proteins allow B. burgdorferi to survive in the variety of hosts by evading the immune system (Steere, 2001). The gene encoding the Osp proteins are found on a 49kb linear plasmid (http://textbookofbacteriology.net/Lyme.html).

Osp A, B, and C are the most common surface proteins seen on B. burgdorferi, but these proteins demonstrate differential expression based on bacterium’s location and stage of the infection cycle.  Osp A and B, which are encoded in a bicistronic operon, are abundant on the bacterial surface within unfed ticks. Upon feeding, the expression of Osp A and B proteins is down-regulated, and Osp C expression is up-regulated.  Osp C is not seen before tick feeding. While OspA and B must persist to some degree due to the presence of Osp A and B antibodies in late-stage Lyme disease patients, Osp A and B seem to be tick-specific, while Osp C is more prevalent in vertebrate hosts such as humans and mice (de Silva and Fikrig, 1997).

This page was created for an undergraduate Immunology course, Biology 307, at Davidson College in the Spring semester of 2007 under Dr. Sophia Sarafova (sasarafova@davidson.edu)

Please direct all comments and questions to Meredith Prasse (meprasse@davidson.edu)