A genus of spirochetes that have a unique genome composed of a linear chromosome and numerous linear and circular plasmids. Borreliae are motile, helical organisms with 4–30 uneven, irregular coils, and are 5–25 micrometers long and 0.2–0.5 μm wide. Their locomotory apparatus consists of 15–22 fibrils coiled around the cell body and situated between the elastic envelope and cytoplasmic membrane. Motion is forward and backward, laterally by bending and looping, and corkscrewlike. Borreliae multiply by binary fission.