Spirochaete

Spirochaetes
	Treponema pallidum, a spirochaete which causes syphilis
Scientific classification
Domain:	Bacteria
Kingdom:	Pseudomonadati
Phylum:	Spirochaetota; Garrity and Holt 2021
Class:	Spirochaetia; Paster 2020
Orders
	Brachyspirales; Brevinematales; Leptospirales; Spirochaetales; "Treponematales";
Synonyms
	Spirochaetota: "Protozoobacteriales" Prévot 1958; "Spirochaetae" Cavalier-Smith 2002; "Spirochaetaeota" Oren et al. 2015; "Spirochaetes" Garrity and Holt 2001; "Spirochaetota" Whitman et al. 2018; Spirochaetia: Spirochaetes Cavalier-Smith 2002; "Spirochaetia" Cavalier-Smith 2020; "Leptospiria" Cavalier-Smith 2020;

Endoflagella Components. Legend: Fig. 1: A cross-section of a typical spirochete cell showing endoflagella located in the periplasm between the inner cytoplasmic membrane and the outer membrane. Periplasm, consisting of a gel-like matrix, provides a semi-stable medium to secure endoflagella during rotation. The axial filament, indicated in red, is composed of bundles of endoflagella.
Fig. 2: A side-view of a spirochete cell which shows two axial filaments in opposing motion. One axial filament rotates in a clockwise orientation; an adjacent axial filament rotates in a counter-clockwise orientation. Rotation of the endoflagella creates torsion and drives the corkscrew rotation of the cell.
Fig. 3: An expanded view of the cellular membranes that surround endoflagellum. Both the inner and outer membrane contain a phospholipid bi-layer, with non-polar fatty acid chains in-ward of polar phosphorus heads. Peptidoglycan, the cell wall, provides structure in bacterial microorganisms. Axial filaments are superior to the peptidoglycan.

A spirochaete (/ˈspaɪroʊˌkiːt/) or spirochete is a member of the phylum Spirochaetota (also called Spirochaetes /ˌspaɪroʊˈkiːtiːz/), which contains distinctive diderm (double-membrane) Gram-negative bacteria, most of which have long, helically coiled (corkscrew-shaped or spiraled, hence the name) cells. Spirochaetes are chemoheterotrophic in nature, with lengths between 3 and 500 μm and diameters around 0.09 to at least 3 μm.

Spirochaetes are distinguished from other bacterial phyla by the location of their flagella, called endoflagella, or periplasmic flagella, which are sometimes called axial filaments. Endoflagella are anchored at each end (pole) of the bacterium within the periplasmic space (between the inner and outer membranes) where they project backwards to extend the length of the cell. These cause a twisting motion which allows the spirochaete to move. When reproducing, a spirochaete will undergo asexual transverse binary fission. Most spirochaetes are free-living and anaerobic, but there are numerous exceptions. Spirochaete bacteria are diverse in their pathogenic capacity and the ecological niches that they inhabit, as well as molecular characteristics including guanine-cytosine content and genome size.