The spirochaetes are a phylum of distinctive bacteria, which have long, helically coiled cells. They are distinguished by the presence of flagella running lengthwise between the cell membrane and cell wall, called axial filaments. These cause a twisting motion which allows the spirochaete to move about. Most spirochaetes are free-living and anaerobic, but there are numerous exceptions.
It has been suggested by Lynn Margulis that eukaryotic flagella were derived from symbiotic spirochaetes, but few biologists accept this, as there is no close structural similarity between the two.
The only class of the spirochaetes phylum is spirochaetes. The only order is spirochaetales. There are three families, brachyspiraceae, leptospiraceae and spirochaetaceae. Important members of this phylum include
- Leptospira species, which causes leptospirosis,
- Borrelia bergdorferi, which causes Lyme disease, and
- Trepomena pallidum, which causes syphilis.
