A spirochaete () or spirochete is a member of the phylum Spirochaetota (also called Spirochaetes ), 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.
Pathogenicity Many organisms within the Spirochaetota phylum cause prevalent diseases. Pathogenic members of this phylum include the following: Leptospira species, which causes leptospirosis Borrelia burgdorferi, B. mayonii, B. bissettiae, B. garinii, B. afzelii, B. spielmanii, B. lusitaniae, which cause Lyme disease. Borrelia recurrentis, which causes relapsing fever Treponema pallidum subspecies which cause treponematoses such as syphilis and yaws. Brachyspira pilosicoli and Brachyspira aalborgi, which cause intestinal spirochaetosis
Salvarsan, the first partially organic synthetic antimicrobial drug in medical history, was effective against spirochaetes and primarily used to cure syphilis. Additionally, oral spirochaetes are known to play a significant role in the pathogenesis of human periodontal disease.
Taxonomy and molecular signatures The class currently consists of 14 validly named genera across four orders and five families. The orders Brachyspirales, Brevinematales and Leptospirales each contain a single family, Brachyspiraceae, Brevinemataceae and Leptospiraceae, respectively. The Spirochaetales order harbours two families, Spirochaetaceae and Borreliaceae. Molecular markers in the form of conserved signature indels (CSIs) and CSPs have been found specific for each of the orders, with the exception of Brevinimetales, that provide a reliable means to demarcate these clades from one another within the diverse phylum. Additional CSIs have been found exclusively shared by each family within the Spirochaetales. These molecular markers are in agreement with the observed phylogenetic tree branching of two monophyletic clades within the Spirochaetales order. CSIs have also been found that further differentiate taxonomic groups within the Borreliaceae family that further delineate evolutionary relationships that are in accordance with physical characteristics such as pathogenicity (viz. Borrelia emend. Borreliella gen. nov.). However, this study has been criticized, and other studies using different approaches do not support the proposed split. The new naming system for the Lyme and relapsing fever Borrelia has not been adopted by the scientific literature.
A CSI has also been found exclusively shared by all Spirochaetota species. This CSI is a three-amino-acid insert in the flagellar basal body rod protein FlgC which is an important part of the unique endoflagellar structure shared by Spirochaetota species. Given that the CSI is exclusively shared by members within this phylum, it has been postulated that it may be related to the characteristic flagellar properties observed among Spirochaetota species.
Historically, all families belonging to the Spirochaetota phylum were assigned to a single order, the Spirochaetales. However, the current taxonomic view is more connotative of accurate evolutionary relationships. The distribution of a CSI is indicative of shared ancestry within the clade for which it is specific. It thus functions as a synapomorphic characteristic, so that the distributions of different CSIs provide the means to identify different orders and families within the phylum and so justify the phylogenetic divisions.
Phylogeny
16S rRNA based LTP_10_2024 120 marker proteins based GTDB 10-RS226
Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). Phylum Spirochaetota Garrity and Holt 2021 Genus ?"Spirosymplokos" Guerrero et al. 1993 Class Leptospiria Chuvochina et al. 2024 Order Turneriellales Chuvochina et al. 2024 Family Turneriellaceae Chuvochina et al. 2024 Genus Turneriella Levett et al. 2005 Order Leptospirales Gupta et al. 2014 Family Leptonemataceae Chuvochina et al. 2024 Genus Leptonema Hovind-Hougen 1983 Family Leptospiraceae Hovind-Hougen 1979 Genus Leptospira Noguchi 1917 Class Brevinematia Chuvochina et al. 2024 Order Brevinematales Gupta et al. 2014 Family "Longinemataceae" Karnachuk et al. 2021 Genus ?"Longinema" corrig. Karnachuk et al. 2021 Family Brevinemataceae Paster 2012 Genus Brevinema Defosse et al. 1995 Family Thermospiraceae Ben Ali Gam et al. 2023 Genus Thermospira Ben Ali Gam et al. 2023 Class Brachyspiria Chuvochina et al. 2024 Order Brachyspirales corrig. Gupta et al. 2014 Family Brachyspiraceae Paster 2012 Genus ?"Ca. Maribrachyspira" Matsuyama et al. 2017 Genus Brachyspira Hovind-Hougen et al. 1982 non Foliella non Pfeiffer 1855 Class Spirochaetia Paster 2020 Order Spirochaetales Buchanan 1917 Family "Pillotinaceae" Margulis & Hinkle 1992 Genus ?Pillotina Hollande and Gharagozlou 1967 ex Bermudes et al. 1988 Family Spirochaetaceae Swellengrebel 1907 ["Thiospirochaetaceae" Pallen, Rodriguez-R & Alikhan 2022] Genus ?"Ca. Allospironema" Paster & Dewhirst 2000 Genus ?"Canaleparolina" Wier, Ashen & Margulis 2000 Genus ?Clevelandina Bermudes et al. 1988 Genus ?Diplocalyx Gharagozlou 1968 ex Bermudes et al. 1988 non Richard 1850 non Presl 1845 Genus ?Hollandina To et al. 1978 ex Bermudes et al. 1988 non Haynes 1956 Genus ?"Mobilifilum" Margulis et al. 1990 Genus ?Rarispira Podosokorskaya et al. 2025 Genus ?"Spirophis" (Warming 1875) Lauterborn 1916 Genus ?Spirochaeta Ehrenberg 1835 em. Pikuta et al. 2009 non Turczaninow 1851 Genus "Ca. Haliotispira" Sharma et al. 2024 Order "Exilispirales" Pallen, Rodriguez-R & Alikhan 2022 Family "Exilispiraceae" Pallen, Rodriguez-R & Alikhan 2022 Genus Exilispira Imachi et al. 2008 Order Borreliales Chuvochina et al. 2024 Family Borreliaceae Gupta et al. 2014 Genus Borrelia Swellengrebel 1907 (relapsing fever Borrelia, reptile-associated Borrelia and Echidna-associated Borrelia) Genus Borreliella Adeolu & Gupta 2015 (Lyme disease Borrelia) Genus ?Cristispira Gross 1910 Order "Entomospirales" Pallen, Rodriguez-R & Alikhan 2022 [WRBN01] Family "Entomospiraceae" Pallen, Rodriguez-R & Alikhan 2022 Genus Entomospira Grana-Miraglia et al. 2024 non Enderlein 1917 Order "Salinispirales" Pallen, Rodriguez-R & Alikhan 2022 [DSM-27196] Family "Thiospirochaetaceae" Pallen, Rodriguez-R & Alikhan 2022 [DSM-19205] Genus Oceanispirochaeta Subhash & Lee 2017b Genus "Ca. Thalassospirochaeta" Pragya et al. 2024 Genus Thiospirochaeta Dubinina et al. 2020 Family Alkalispirochaetceae Chuvochina et al. 2024 Genus Alkalispirochaeta Sravanthi et al. 2016 Family Salinispiraceae Chuvochina et al. 2024 Genus Salinispira Ben Hania et al. 2015 Order Winmispirales Podosokorskaya et al. 2025 [DSM-6578] Family Winmispiraceae Podosokorskaya et al. 2025 Genus Winmispira Podosokorskaya et al. 2025 Order "Sediminispirochaetales" Pallen, Rodriguez-R & Alikhan 2022 Family Sediminispirochaetaceae Chuvochina et al. 2024 Genus Sediminispirochaeta Shivani et al. 2016 Order "Marispirochaetales" Pallen, Rodriguez-R & Alikhan 2022 Family Marispirochaetaceae Chuvochina et al. 2024 Genus Marispirochaeta Shivani et al. 2017 Order Sphaerochaetales Chuvochina et al. 2024 Family Sphaerochaetaceae Hördt et al. 2020 Genus Bullifex Wylensek et al. 2021 [incl. "Ca. Aphodenecus" Gilroy et al. 2021] Genus "Ca. Ornithospirochaeta" Gilroy et al. 2021 Genus Parasphaerochaeta Bidzhieva et al. 2020 Genus ?"Ca. Physcosoma" Gilroy et al. 2022 Genus ?Pleomorphochaeta Arroua et al. 2016 Genus Sphaerochaeta Ritalahti et al. 2012 Order Treponematales Chuvochina et al. 2024 Family Rectinemataceae Brune et al. 2022 Genus Rectinema Koelschbach et al. 2017 Family Breznakiellaceae Brune et al. 2022 Genus Breznakiella Song et al. 2022 Genus Gracilinema Brune et al. 2022 Genus ?Helmutkoenigia Brune et al. 2022 Genus Leadbettera Brune et al. 2022 Genus ?"Propulsinema" Fu et al. 2025 Genus ?Zuelzera Brune et al. 2022 Family Treponemataceae Robinson 1948 Genus "Ca. Avitreponema" Gilroy et al. 2021 Genus Brucepastera Song et al. 2023 Genus "Ca. Gallitreponema" Gilroy et al. 2021 Genus Teretinema Song et al. 2023 Genus Treponema Schaudinn 1905 em. Abt et al. 2013
See also
List of bacteria genera List of bacterial orders Bacteriology Borrelia Brevinema andersonii Flagellum Lyme disease microbiology Pinta (disease) Prokaryote Syphilis Treponema pallidum Yaws
References
External links Introduction to the Spirochetes University of California Museum of Paleontology (UCMP)