A spirochaete () or spirochete is a member of the

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Spirochaetota (also called Spirochaetes ), which contains distinctive diderm (double-membrane)

Gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...

, 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 niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

s 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 Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms depend on the stage it presents: primary, secondary, latent syphilis, latent or tertiary. The prim ...

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

. 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 A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor Wi ...

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

Taxonomy

The currently accepted taxonomy is based on the

List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

(LPSN) and

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is lo ...

(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 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 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 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 Pallen, Rodriguez-R & Alikhan 2022">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 ?"''Candidatus'' Haliotispira" Sharma et al. 2024 ***** Genus ?'' Hollandina'' To et al. 1978 ex Bermudes et al. 1988 non Haynes 1956 ***** Genus ?"'' Mobilifilum''" Margulis et al. 1990 ***** Genus '' Oceanispirochaeta'' Subhash & Lee 2017b ***** Genus ?'' Spirochaeta'' Ehrenberg 1835 em. Pikuta et al. 2009 non Turczaninow 1851 ***** Genus ?"''Candidatus'' 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 "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 **** Family "Entomospiraceae" Pallen, Rodriguez-R & Alikhan 2022 ***** Genus '' Entomospira'' Grana-Miraglia et al. 2024 non Enderlein 1917 *** Order "Marispirochaetales" Pallen, Rodriguez-R & Alikhan 2022 **** Family Marispirochaetaceae Chuvochina et al. 2024 ***** Genus '' Marispirochaeta'' Shivani et al. 2017 *** Order "Sediminispirochaetales" Pallen, Rodriguez-R & Alikhan 2022 **** Family Sediminispirochaetaceae Chuvochina et al. 2024 ***** Genus '' Sediminispirochaeta'' Shivani et al. 2016 *** Order Sphaerochaetales Chuvochina et al. 2024 **** Family Sphaerochaetaceae Hördt et al. 2020 ***** Genus '' Bullifex'' Wylensek et al. 2021 Gilroy et al. 2021">ncl. "''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 '' 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

References

External links