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DNA characterization of the spirochete that causes Lyme disease
Abstract:
Lyme disease, a tick-borne disease long recognized in Europe but only recently recognized in the United States, was shown in 1982-1983 to be caused by a spirochete, the Lyme disease spirochete. Whether one or more species of the spirochete exists is unknown, as is its taxonomic status. To answer these questions, we determined (i) the DNA base (guanidine-plus-cytosine) content for five strains; (ii) the DNA relatedness of 10 strains from Europe or the United States (isolated from ticks, humans, and a mouse) by DNA hybridization (hydroxyapatite assay at 50 and 65 degrees C); and (iii) the DNA relatedness to other pathogenic spirochetes. The guanine-plus-cytosine content of the Lyme disease spirochete strains was 27.5 to 29.0 mol%, most similar to those of Borrelia hermsii (30.6 mol%) and Treponema hyodysenteriae (25.6 mol%) among the other spirochetes tested. DNA hybridization studies with 32P-labeled DNA from Lyme disease spirochete strain TLO-005, a human blood isolate, revealed divergence (unpaired bases) within related nucleotide sequences of only 0.0 to 1.0% for all nine Lyme disease spirochete strains tested for relatedness to TLO-005. Relatedness values of seven strains to TLO-005 were 58 to 98% (mean, 71%) in 50 degrees C reactions and 50 to 93% (mean, 69%) in 65 degrees C reactions. Two other strains, from which very low yields of DNA were obtained, showed less relatedness (36 to 50 degrees C, 38 to 47% at 65 degrees C). These were nonetheless considered to belong to the same species because of the low amount of divergence in the sequences related to TLO-005 and the absence of decreased relatedness in reactions done at 65 degrees Celsius compared with those done at 50 degrees Celsius. DNA from strain TLO-005 showed relatedness of 1% to DNAs of two leptospires and 16% relatedness to DNA from T. hyodysenteriae. B. hermsii DNA was 30 to 40% related to three Lyme disease spirochete strains in 50 degrees Celsius reactions. Divergence in these reactions was 16.5 to 18.5%, and relatedness in 65 degree Celsius reactions was 8 to 10%. On the bases of phenotypic similarity, guanine-plus-cytosine content, and DNA relatedness to B. hermsii, we conclude the Lyme disease spirochete is single previously undescribed species which belongs in the genus Borrelia.
Insights
Researchers investigated the Lyme disease spirochete, a cause of Lyme disease, to determine its species and taxonomic status. DNA analysis confirmed it is a single, previously undescribed species within the Borrelia genus.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Lyme disease is a significant tick-borne illness recognized in Europe and the United States.
- The causative agent, the Lyme disease spirochete, was identified in 1982-1983.
- The exact species and taxonomic classification of the Lyme disease spirochete remained undetermined.
Purpose of the Study:
- To ascertain if the Lyme disease spirochete represents one or more species.
- To establish the taxonomic status of the Lyme disease spirochete.
- To compare DNA characteristics of different spirochete strains.
Main Methods:
- Determined Guanine-plus-cytosine (G+C) content for five spirochete strains.
- Performed DNA hybridization (hydroxyapatite assay) on 10 strains from diverse origins.
- Assessed DNA relatedness to other pathogenic spirochetes, including Borrelia hermsii and Treponema hyodysenteriae.
Main Results:
- Lyme disease spirochete strains exhibited G+C content between 27.5-29.0 mol%, similar to Borrelia species.
- DNA hybridization showed high relatedness (58-98%) among nine Lyme disease spirochete strains, indicating a single species.
- Low DNA relatedness (1-16%) was observed between Lyme disease spirochete and other genera like Leptospira and Treponema.
Conclusions:
- The Lyme disease spirochete is a single, previously undescribed species.
- Based on phenotypic similarity, G+C content, and DNA relatedness, the species belongs to the genus Borrelia.
- This classification clarifies the taxonomic status of the Lyme disease agent.