Genomic sequence of a Lyme disease spirochaete, Borrelia burgdorferi

Abstract

The genome of the bacterium Borrelia burgdorferi B31, the aetiologic agent of Lyme disease, contains a linear chromosome of 910,725 base pairs and at least 17 linear and circular plasmids with a combined size of more than 533,000 base pairs. The chromosome contains 853 genes encoding a basic set of proteins for DNA replication, transcription, translation, solute transport and energy metabolism, but, like Mycoplasma genitalium, it contains no genes for cellular biosynthetic reactions. Because B. burgdorferi and M. genitalium are distantly related eubacteria, we suggest that their limited metabolic capacities reflect convergent evolution by gene loss from more metabolically competent progenitors. Of 430 genes on 11 plasmids, most have no known biological function; 39% of plasmid genes are paralogues that form 47 gene families. The biological significance of the multiple plasmid-encoded genes is not clear, although they may be involved in antigenic variation or immune evasion.

Functional and evolutionary roles of long repeats in prokaryotes

“…Bacteria present very diverse evolutionary strategies linked to pathogenesis, such as: pathogenicity islands in Salmonella and E. coli [17], and Vibrio cholerae [18], gene uptake systems in V. cholerae [19], tandem repeats for phase variation in Haemophilus influenzae [20], tandem repeats linked with contingency loci in H. pylori [10,21], and long repeats for antigenic variation in Mycoplasma [9,22], B. burgdorferi [23], and M. tuberculosis [12].…”

“…Though the genome analysis has revealed very few repeats in the chromosome, the plethora of linear and circular plasmids that add up to more than 600 kb of genetic material contain a very large amount of repeated sequences [23]. These plasmids possess lower densities of genes (70%) [23] of which many code for surface proteins, therefore paving the way for a global strategy of antigenic variation ( figure 1).…”

“…Though the genome analysis has revealed very few repeats in the chromosome, the plethora of linear and circular plasmids that add up to more than 600 kb of genetic material contain a very large amount of repeated sequences [23]. These plasmids possess lower densities of genes (70%) [23] of which many code for surface proteins, therefore paving the way for a global strategy of antigenic variation ( figure 1). The accumulation of recombinant genetic material in plasmids has the important advantage of removing most of the genetic rearrangements from the chromosome, thereby stabilising it, which may be particularly important for this linear chromosome.…”

Biology of Infection with Borrelia burgdorferi

“…Despite the atypical DNA form, the majority of genes encoded on the B. burgdorferi chromosome are commonly found in other bacterial genomes [4]. The genes encoded on the plasmid component of the genome are less recognizable and the majority of these appear to be unique to the genus Borrelia [4,5].…”

“…Consistent with the pathogenesis of Lyme disease, bacterial products that allow B. burgdorferi to replicate and survive, rather than true "virulence factors," appear to be primarily what is required for the bacterium to cause disease in a susceptible host. In support of this idea, the genome sequence of B31, the type strain of B. burgdorferi sensu stricto [4,5], revealed that the bacterium lacks factors common to many bacterial pathogens, such as lipopolysaccharide, toxins, and specialized secretion systems. In this chapter, we will describe the basic biology of B. burgdorferi, and some of the bacterial components required to infect and survive in the mammalian and tick hosts.…”