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Genome sequencing

New tricks of tick-borne pathogen

Nature volume 390, pages 553–554 (1997)Cite this article

But those who were expecting to find in B. burgdorferi a rich vein of gold in which to mine virulence determinants have to be disappointed. The sequence is as notable for what it does not contain as for what it does. Instead of finding many orthologues4 of toxin and invasion genes, global regulatory systems, two-component signal-transduction pathways and bacteriophages of other pathogenic bacteria, the authors found an almost bewildering array of duplicated lipoprotein genes, unique to Borrelia spp. and of unknown function. These genes are located on extrachromosomal stretches of DNA called plasmids. One of the lipoproteins, OspA, has already been crystallized and structurally characterized5, and it is undergoing human field trials as a vaccine against Lyme disease, although no one yet knows what it does.

Discovery of the linear chromosome in Borrelia6,7 challenged ideas of what a bacterial chromosome is. The findings of Fraser et al.3 now provide further evidence that the distinction between a plasmid and chromosome is primarily a matter of size. The linear and circular plasmids of Borrelia spp. are equimolar with chromosomes8,9, they contain genes that are usually found on chromosomes (for example, guaA and tRNAGly), and they have apparently undergone recombination with the chromosome. These elements could equally be examples of minichromosomes as of plasmids, and they seem to provide an opportunity and place for the organism to duplicate genes and rearrange them without much cost or damage. Moreover, by possessing several copies of highly similar genes on the same (and different) elements, there is the potential for diverse antigenic variation — and this has been observed in relapsing fever Borrelia spp.10.

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Figure 1: Life cycle of Ixodes tick vectors of Borrelia burgdorferi, the spirochaete agent of Lyme disease that has now been sequenced by Fraser et al.3.

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  1. the Departments of Microbiology and Molecular Genetics and Medicine, University of California, Irvine, 92697-4025, California, USA

    Alan G. Barbour & Wolfram R. Zückert

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  1. Alan G. Barbour
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  2. Wolfram R. Zückert
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Barbour, A., Zückert, W. New tricks of tick-borne pathogen. Nature 390, 553–554 (1997). https://doi.org/10.1038/37475

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