spirochete

[spahy-ruh-keet]

Scanning electron micrograph of the spirochete Treponema pallidum attached to testicular elipsis

Any of an order (Spirochaetales) of spiral-shaped bacteria. Some are serious pathogens for humans, causing such diseases as syphilis, yaws, and relapsing fever. Spirochetes are gram-negative (see gram stain) and motile. They are unique in that their flagella, which number between two and more than 200 per organism, are contained within the cell. Most spirochetes are found in a liquid environment (e.g., mud and water, blood and lymph). Several species are borne by lice and ticks, which transmit them to humans.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Spirochaete

Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long, helically coiled cells. Spirochetes are chemoheterotrophic in nature, with lengths between 5 and 250 µm and diameters around 0.1-0.6 µm.

Spirochaetes are distinguished from other bacterial phyla by the location of their flagella, sometimes called axial filaments, which run lengthwise between the cell membrane and outer membrane. These cause a twisting motion which allows the spirochaete to move about. When reproducing, a spirochaete will undergo asexual transverse binary fission.

The spirochaetes are divided into three families (Brachyspiraceae, Leptospiraceae, and Spirochaetaceae), all placed within a single order (Spirochaetales). Disease-causing members of this phylum include the following:

Leptospira species, which causes leptospirosis
Borrelia burgdorferi, which causes Lyme disease
Borrelia recurrentis, which causes relapsing fever
Treponema pallidum, which causes syphilis
Treponema pertenue, which causes yaws

Most spirochaetes are free-living and anaerobic, but there are numerous exceptions, including the above.

Cavalier-Smith has postulated that the Spirochaetes belong in a larger clade called Gracilicutes.

Historical

Salvarsan, the first antibiotic in medical history, was effective against spirochaetes only and was primarily used to cure syphilis.

It has been suggested by biologist 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.