Genetic studies were performed on the following spirochetes: three
Lyme disease spirochetes isolated from Ixodes ticks and from human spinal fluid; three species of North American borreliae; four species of Treponema; and two species of Leptospira. The mol% G+C values for
Lyme disease spirochetes were 27.3 to 30.5%, similar to values of 28.0 to 30.5% for Borrelia species but different from the values of Leptospira or Treponema species which ranged from 35.3 to 53%.
Lyme disease spirochetes represent a new species of Borrelia, with DNA homologies of 31 to 59% with the three North American strains of Borrelia studied. These studies also showed that
Lyme disease spirochetes from three sources constituted a single species, with DNA homologies ranging from 76 to 100%. A high degree of relatedness was also seen between the three North American borreliae, with homology varying from 77 to 95%, indicating that these spirochetes represent a single species.
Lyme disease spirochetes and Borrelia species exhibited almost no homology with Leptospira and Treponema species (0 to 2%). Plasmids were detected in the three
Lyme disease spirochetes and in the three North American borreliae.