Borrelia burgdorferi: a (somewhat) clonal bacterial species

Abstract

In their recent review article, Dykhuizen and Baranton 1xThe implications of a low rate of horizontal transfer in Borrelia. Dykhuizen, D.E. and Baranton, G. Trends Microbiol. 2001; 9: 344–350Abstract | Full Text | Full Text PDF | PubMed | Scopus (68)See all References1 reviewed the evidence for DNA exchange between Borrelia burgdorferi, most of which I agree with completely. I would, however, like to point out to readers that, although the authors refer to many of the different variants of Lyme disease spirochetes as separate species, not all researchers in the field agree with this divisive system.Genetic variants are probably indicative of different lineages, but there is no evidence that the identified differences are significant enough to warrant the division of Lyme disease spirochetes into multiple species. A growing number of species names have been proposed, based on such criteria as the sequence of a non-coding chromosomal region (the rrfA–rrlB intergenic region) or the presence of certain restriction sites in the chromosome 2xMolecular typing of Borrelia burgdorferi sensu lato: taxonomic, epidemiological, and clinical implications. Wang, G. et al. Clin. Microbiol. Rev. 1999; 12: 633–653PubMedSee all References2. Under such definitions, a bacterium could change species as a result of only a few point mutations. Additionally, some genetic loci used for definition of species are known to be exchanged between distantly related bacteria 1xThe implications of a low rate of horizontal transfer in Borrelia. Dykhuizen, D.E. and Baranton, G. Trends Microbiol. 2001; 9: 344–350Abstract | Full Text | Full Text PDF | PubMed | Scopus (68)See all References, 2xMolecular typing of Borrelia burgdorferi sensu lato: taxonomic, epidemiological, and clinical implications. Wang, G. et al. Clin. Microbiol. Rev. 1999; 12: 633–653PubMedSee all References, 3xBorrelia burgdorferi is clonal: implications for taxonomy and vaccine development. Dykhuizen, D.E. et al. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 10163–10167Crossref | PubMed | Scopus (115)See all References, 4xTwo distinct ospA genes among Borrelia valaisiana strains. Wang, G. et al. Res. Microbiol. 2000; 151: 325–331Crossref | PubMed | Scopus (14)See all References, so an organism can be assigned to two or more ‘species’ depending upon the criterion used 4xTwo distinct ospA genes among Borrelia valaisiana strains. Wang, G. et al. Res. Microbiol. 2000; 151: 325–331Crossref | PubMed | Scopus (14)See all References4. Most importantly, despite numerous attempts, the various manifestations of Lyme disease in humans cannot be conclusively attributed to infections with specific types of bacteria: different variants have been identified from patients with many similar symptoms 2xMolecular typing of Borrelia burgdorferi sensu lato: taxonomic, epidemiological, and clinical implications. Wang, G. et al. Clin. Microbiol. Rev. 1999; 12: 633–653PubMedSee all References, 5xNondifferentiation between Lyme disease spirochetes from vector ticks and human cerebrospinal fluid. Eiffert, H. et al. J. Infect. Dis. 1995; 171: 476–479Crossref | PubMed | Scopus (63)See all References, 6xDirect molecular typing of Borrelia burgdorferi sensu lato species in synovial samples from patients with lyme arthritis. Jaulhac, B. et al. J. Clin. Microbiol. 2000; 38: 1895–1900PubMedSee all References, 7xScored antibody reactivity determined by immunoblotting shows an association between clinical manifestations and presence of Borrelia burgdorferi sensu stricto, B. garinii, B. afzelii, and B. valaisiana in humans. Ryffel, K. et al. J. Clin. Microbiol. 1999; 37: 4086–4092PubMedSee all References. For these reasons, it is more appropriate that these genetic variants be called ‘genovars’ of a single species, B. burgdorferi. Viewing all these bacteria as members of a single species, which can encounter each other in the same warm-blooded and arthropod hosts in nature, makes it easy to understand how genetic exchanges can occur.As Dykhuizen and Baranton so well explain, the chromosome and some plasmids of B. burgdorferi are largely clonal, with very little variation among, and between, genovars 1xThe implications of a low rate of horizontal transfer in Borrelia. Dykhuizen, D.E. and Baranton, G. Trends Microbiol. 2001; 9: 344–350Abstract | Full Text | Full Text PDF | PubMed | Scopus (68)See all