Bacteria Genomes - BORRELIA BURGDORFERI

Borrelia burgdorferi is a Gram-negative spirochete which is the causative agent of Lyme disease, the most common tick-borne disease in the United States. The reservoir for the spirochete is the white-footed mouse and the white-tailed deer. Transmission is accomplished by the bite of infected deer ticks. Contact with the tick usually occurs in areas of brush and tall grass.

The disease is usually recognised by a distinctive skin lesion, erythema migrans, accompanied by headache, stiff neck, myalgias, arthralgias, fatigue and possible swelling of the lymph nodes. While treatable with antibiotics, unrecognised and/or untreated patients may develop meningoencephalitis, myocarditis or even arthritis, particularly in the knees. Lyme disease may be brief or inconsequential, or chronic, persistent and incapacitating. In a small percentage of cases, there is no resolution even after antibiotic treatment.

Borrelia burgdorferi have been isolated and cultured from the mid-gut of Ixodes ticks, and subsequently from patients with Lyme disease in the early-1980s. Borrelia burgdorferi resembles other spirochetes in that it is a highly specialised, motile, two-membrane, spiral-shaped bacteria which lives primarily as an extracellular pathogen. One of the most striking features of Borrelia burgdorferi as compared with other eubacteria is its unusual genome, which includes a linear chromosome approximately one megabase in size and numerous linear and circular plasmids.

Long-term culture of Borrelia burgdorferi results in a loss of some plasmids and changes in expressed protein profiles. Associated with the loss of plasmids is a loss in the ability of the organism to infect laboratory animals, suggesting that the plasmids encode key genes involved in virulence.

Borrelia burgdorferi grows slowly compared to most bacteria. Each spirochete divides into two cells after 12 to 24 hours of elongation. Although the organism can be cultured in media, continuous passage may result in biological changes resulting in a population quite different from their naturally occurring ancestors.

References:
http://www.tigr.org/tdb/CMR/gbb/htmls/Background.html
http://www.wadsworth.org/databank/borreli.htm
www.cdc.gov
Int. J. System. Bacteriol. 34: 496-497 (1984)
Nature 390(6660):580-586(1997).