# Chloroflexota

The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photosynthesis (green non-sulfur bacteria); and anaerobic halorespirers, which uses halogenated organics (such as the toxic chlorinated ethenes and polychlorinated biphenyls) as electron acceptors.
The members of the phylum Chloroflexota are monoderms (that is, have one cell membrane with no outer membrane), but they stain mostly gram-negative. Many well-studied phyla of bacteria are diderms and stain gram-negative, whereas well-known monoderms that stain Gram-positive include Firmicutes (or Bacillota) (low G+C gram-positives), Actinomycetota (high-G+C gram-positives) and Deinococcota (gram-positive diderms with thick peptidoglycan).

## History

The taxon name was created in the 2001 edition of Volume 1 of Bergey's Manual of Systematic Bacteriology and is the Latin plural of the name Chloroflexus, the name of the type genus of the phylum, a common practice.
In 1987, Carl Woese, regarded as one of the forerunner of the molecular phylogeny revolution, divided Eubacteria into 11 divisions based on 16S ribosomal RNA (SSU) sequences and grouped the genera Chloroflexus, Herpetosiphon and Thermomicrobium into the "green non-sulfur bacteria and relatives", which was temporarily renamed as "Chloroflexi" in Volume One of Bergey's Manual of Systematic Bacteriology.
Chloroflexota being a deep branching phylum (see Bacterial phyla), it was considered in Volume One of Bergey's Manual of Systematic Bacteriology to include a single class with the same name. Since 2001, however, new classes have been created thanks to newly discovered species, and the phylum Chloroflexi is now divided into several classes.
"Dehalococcoidetes" is a placeholder name given by Hugenholtz & Stackebrandt, 2004, after "Dehalococcoides ethenogenes" a species partially described in 1997. The first species fully described was Dehalogenimonas lykanthroporepellens, by Moe et al. 2009, but in the description of that species the class was not made official nor were families or orders laid out as the two species share only 90% 16S ribosomal RNA identity, meaning that they could fall in different families or even orders.
Recent phylogenetic analysis of the Chloroflexota has found very weak support for the grouping together of the different classes currently part of the phylum. The six classes that make up the phylum did not consistently form a well-supported clade in phylogenetic trees based on concatenated sequences for large datasets of proteins, and no conserved signature indels were identified that were uniquely shared by the entire phylum. However, the classes Chloroflexi and Thermomicrobia were found to group together consistently by both the usual phylogenetic means and the identification of shared conserved signature indels in the 50S ribosomal protein L19 and the enzyme UDP-glucose 4-epimerase. It has been suggested that the phylum Chloroflexi sensu stricto should comprise only the classes Chloroflexi and Thermomicrobia, and the other four classes ("Dehalococcoidetes," Anaerolineae, Caldilineae and Ktedonobacteria) may represent one or more independent phyla branching in the neighborhood of the Chloroflexi.

## Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI).
| 16S rRNA based LTP_10_2024 | 120 marker proteins based GTDB 09-RS220 |
| Thermoflexia Thermoflexales Thermoflexaceae Thermoflexus Chloroflexota "Thermomicrobiia" Sphaerobacterales Sphaerobacteraceae Sphaerobacter Nitrolancea Thermomicrobiales Thermomicrobiaceae Thermalbibacter Thermomicrobium Thermorudis Chloroflexia Kallotenuales Kallotenuaceae Kallotenue Herpetosiphonales Herpetosiphonaceae Herpetosiphon Chloroflexales Roseiflexaceae Roseiflexus Chloroflexaceae Heliothrix Oscillochloris Chloroflexus Ktedonobacteria Thermogemmatisporales Thermogemmatisporaceae Thermogemmatispora Ktedonobacteriales Thermosporotrichaceae Thermosporothrix Ktedonosporobacteraceae Ktedonosporobacter Reticulibacteraceae Reticulibacter Ktedonobacteraceae Ktedonobacter Ktedonospora Dictyobacteraceae Tengunoibacter Dictyobacter Tepidiformia Tepidiformales Tepidiformaceae Tepidiforma Dehalococcoidia Dehalococcoidales Dehalococcoidaceae Dehalococcoides Dehalogenimonas "Caldilineia" Caldilineales Caldilineaceae Litorilinea Caldilinea Ardenticatenia Aggregatilineales Aggregatilineaceae Aggregatilinea Ardenticatenales Ardenticatenaceae Ardenticatena "Anaerolineia" Anaerolineales Anaerolineaceae Thermomarinilinea Flexilinea Ornatilinea Pelolinea Anaerolinea Leptolinea Levilinea Bellilinea Longilinea | "Dormibacteria" "Dormibacterales" "Dormibacteraceae" "Ca Dormiibacter" "Limnocylindria" "Limnocylindrales" "Limnocylindraceae" "Ca Aquidulcis" Ktedonobacteria Ktedonobacteriales Ktedonobacteriaceae Thermogemmatispora Ktedonosporobacter Ktedonobacter Thermosporothrix Tengunoibacter Dictyobacter Chloroflexia "Thermobaculales" "Thermobaculaceae" Thermobaculum Thermomicrobiales Thermomicrobiaceae Nitrolancea Sphaerobacter Thermalbibacter Thermomicrobium Thermorudis Chloroflexales Kallotenuaceae Kallotenue Herpetosiphonaceae Herpetosiphon Roseiflexaceae Roseiflexus "Ca. Ribeiella" "Kouleothrix" Chloroflexaceae Chloroflexus Oscillochloris "Ca. Chloroploca" "Ca. Viridilinea" Dehalococcoidia Tepidiformales Tepidiformaceae "Ca. Amarobacillus" Tepidiforma Dehalococcoidales Dehalococcoidaceae Dehalococcoides Dehalogenimonas "Lucifugimonadales" "Lucifugimonadaceae" "Ca. Lucifugimonas" [SAR202; UBA1151] "Australimonadales" "Australimonadaceae" "Ca. Australimonas" [UBA2963] "Monstramariales" "Monstramariaceae" "Carboxydicoccus" [UBA11650] "Caldilineia" ⊞⊟ Ardenticatenales Ardenticatenaceae Ardenticatena "Epilineales" "Epilineaceae" "Ca. Avedoeria" "Ca. Epilinea" "Caldilineidae" Caldilineales Caldilineaceae Litorilinea "Ca. Fredericiella" Caldilinea "Anaerolineidae" J036 "Roseilineaceae" "Ca. Brachythrix" "Ca. Roseilinea" Thermoflexales Thermoflexaceae Thermoflexus "Promineofilales" "Promineofilaceae" "Ca. Hadersleviella" "Ca. Trichofilum" "Ca. Promineifilum" "Ca. Leptofilum" "Ca. Leptovillus" Aggregatilineales Aggregatilineaceae Aggregatilinea "Phototrophicaceae" "Ca. Flexifilum" "Ca. Flexicrinis" ""Phototrophicus" Anaerolineales "Villigracilaceae" "Desulfolinea" "Ca. Denitrolinea" "Ca. Defluviilinea" "Ca. Villigracilis" Anaerolineaceae Flexilinea "Brevefilum" Pelolinea Ornatilinea Levilinea Leptolinea Anaerolinea Longilinea Bellilinea "Thermanaerothrix" |

## Taxonomy

Genus "Candidatus Caldibacter" corrig. Spieck et al. 2020 Genus "Candidatus Chlorotrichoides" corrig. Oren et al. 2020 ["Candidatus Chlorothrix" Klappenbach & Pierson 2004 non Dyar 1921 non Berger-Perrot 1982] Genus "Candidatus Nitrocaldera" Spieck et al. 2020 Genus "Candidatus Nitrotheca" Spieck et al. 2020 Class "Bathosphaeria" Mehrshad et al. 2018
* Order "Bathosphaerales" Mehrshad et al. 2018
** Family "Bathosphaeraceae" Mehrshad et al. 2018
*** Genus ?"Candidatus Bathosphaera" Mehrshad et al. 2018 (JG30-KF-CM66)
Class "Martimicrobia" Williams et al. 2024
* Order "Martimicrobiales" Williams et al. 2024
** Family "Martimicrobiaceae" Williams et al. 2024
*** Genus ?"Candidatus Laranimicrobium" Williams et al. 2024
*** Genus ?"Candidatus Martimicrobium" Williams et al. 2024
Class "Poriflexia" Mehrshad et al. 2018
* Genus ?"Candidatus Poriflexus" Kogawa et al. 2022
Class "Spiritibacteria" Williams et al. 2024
* Order "Spiritibacterales" Williams et al. 2024
** Family "Spiritibacteraceae" Williams et al. 2024
*** Genus ?"Candidatus Aglaurobacter" Williams et al. 2024
*** Genus ?"Candidatus Otrerea" Williams et al. 2024
*** Genus ?"Candidatus Spiritibacter" Williams et al. 2024
Class "Tarhunnaeia" Williams et al. 2024
* Order "Tarhunnaeales" Williams et al. 2024
** Family "Tarhunnaeaceae" Williams et al. 2024
*** Genus ?"Candidatus Sutekhia" Williams et al. 2024
*** Genus ?"Candidatus Tarhunnaea" Williams et al. 2024
Class "Uliximicrobia" Williams et al. 2024
* Order "Uliximicrobiales" Williams et al. 2024
** Family "Uliximicrobiaceae" Williams et al. 2024
*** Genus ?"Candidatus Uliximicrobium" Williams et al. 2024
Class "Umbricyclopia" Mehrshad et al. 2018
* Order "Umbricyclopales" Mehrshad et al. 2018
** Family "Umbricyclopaceae" Mehrshad et al. 2018
*** Genus ?"Candidatus Umbricyclops" Mehrshad et al. 2018 (TK10)
Class "Limnocylindria" Mehrshad et al. 2018
* Order "Limnocylindrales" Mehrshad et al. 2018
** Family "Limnocylindraceae" Mehrshad et al. 2018 (SL56)
*** Genus "Candidatus Aquidulcis" corrig. Rodriguez-R et al. 2020
*** Genus "Candidatus Limnocylindrus" Mehrshad et al. 2018
Class Ktedonobacteria Cavaletti et al. 2007 emend. Yabe et al. 2010
* Order Thermogemmatisporales Yabe et al. 2011
** Family Thermogemmatisporaceae Yabe et al. 2011
*** Genus Thermogemmatispora Yabe et al. 2011
* Order Ktedonobacterales Cavaletti et al. 2007
** Family Dictyobacteraceae Wang et al. 2019
*** Genus Dictyobacter Yabe et al. 2017
*** Genus Tengunoibacter Wang et al. 2019
** Family Ktedonobacteriaceae Cavaletti et al. 2007
*** Genus Ktedonobacter corrig. Cavaletti et al. 2007
*** Genus Ktedonospora Yabe et al. 2021
** Family Ktedonosporobacteraceae Yan et al. 2020
*** Genus Ktedonosporobacter Yan et al. 2020
** Family Reticulibacteraceae Yabe et al. 2021
*** Genus ?Reticulibacter Yabe et al. 2021
** Family Thermosporotrichaceae Yabe et al. 2010
*** Genus Thermosporothrix Yabe et al. 2010
Class Thermomicrobiia Oren, Parte & Garrity 2016
* Order Sphaerobacterales Stackebrandt, Rainey & Ward-Rainey 1997
** Family Sphaerobacteraceae Stackebrandt, Rainey & Ward-Rainey 1997
*** Genus Nitrolancea Sorokin et al. 2014 ["Nitrolancetus" Sorokin et al. 2012]
*** Genus Sphaerobacter Demharter et al. 1989
* Order Thermomicrobiales Garrity & Holt 2002
** Family Thermomicrobiaceae Garrity & Holt 2002
*** Genus Thermalbibacter Zhao et al. 2023
*** Genus Thermomicrobium Jackson, Ramaley & Meinschein 1973
*** Genus Thermorudis King & King 2014
Class Chloroflexia Gupta et al. 2013
* Genus ?"Candidatus Chlorohelix" Tsuji et al. 2024
* Genus ?"Dehalobium" Wu et al. 2002
* Genus ?"Candidatus Lithoflexus" Saghai et al. 2020
* Genus ?"Candidatus Sarcinithrix" Nierychlo et al. 2019
* Order "Thermobaculales" Chuvochina et al. 2023
** Family "Thermobaculaceae" Chuvochina et al. 2023
*** Genus "Thermobaculum" Botero et al. 2004
* Order Kallotenuales Cole et al. 2013
** Family Kallotenuaceae Cole et al. 2013
*** Genus Kallotenue Cole et al. 2013
* Order Herpetosiphonales Gupta et al. 2013
** Family Herpetosiphonaceae Gupta et al. 2013
*** Genus "Candidatus Anthektikosiphon" Ward, Fischer & McGlynn 2020
*** Genus Herpetosiphon Holt & Lewin 1968 [Flavilitoribacter García-López et al. 2020]
* Order Chloroflexales Gupta et al. 2013
** Suborder Roseiflexineae Gupta et al. 2013
*** Family Roseiflexaceae Gupta et al. 2013 ["Kouleotrichaceae" Mehrshad et al. 2018]
**** Genus ?Heliothrix Pierson et al. 1986
**** Genus "Kouleothrix" Kohno et al. 2002
**** Genus "Candidatus Ribeiella" Petriglieri et al. 2023
**** Genus Roseiflexus Hanada et al. 2002
** Suborder Chloroflexineae Gupta et al. 2013
*** Family Chloroflexaceae Gupta et al. 2013
**** Genus ?"Candidatus Chloranaerofilum" Thiel et al. 2016
**** Genus Chloroflexus Pierson & Castenholz 1974 ["Chlorocrinis"]
*** Family Oscillochloridaceae Gupta et al. 2013
**** Genus ?Chloronema ♪ Dubinina & Gorlenko 1975
**** Genus "Candidatus Chloroploca" Gorlenko et al. 2014
**** Genus Oscillochloris Gorlenko & Pivovarova 1989
**** Genus "Candidatus Viridilinea" Grouzdev et al. 2018
Class Tepidiformia Kochetkova et al. 2020
* Order Tepidiformales Kochetkova et al. 2020
** Family Tepidiformaceae Kochetkova et al. 2020
*** Genus "Candidatus Amarobacillus" Petriglieri et al. 2023
*** Genus ?"Candidatus Amarobacter" Petriglieri et al. 2023
*** Genus "Tepidiforma Kochetkova et al. 2020
Class Dehalococcoidia Löffler et al. 2013
* Order Dehalococcoidales Löffler et al. 2013
** Family Dehalococcoidaceae Löffler et al. 2013
*** Genus Dehalococcoides Löffler et al. 2013
*** Genus Dehalogenimonas Moe et al. 2009
* Order "Lucifugimonadales" Lim et al. 2023
** Family "Lucifugimonadaceae" Lim et al. 2023
*** Genus "Candidatus Lucifugimonas" Lim et al. 2023 [SAR202; UBA1151]
* Order "Australimonadales" Prabhu et al. 2024
** Family "Australimonadaceae" Prabhu et al. 2024
*** Genus "Candidatus Australimonas" Prabhu et al. 2024 [UBA2963]
* Order "Monstramariales" Landry et al. 2017 [SAR202 group III; UBA3495]
** Family "Monstramariaceae" Landry et al. 2017
*** Genus "Carboxydicoccus" Dede et al. 2024 [UBA11650]
Class Ardenticatenia Kawaichi et al. 2013
* Order Ardenticatenales Kawaichi et al. 2013
** Family Ardenticatenaceae Kawaichi et al. 2013
*** Genus Ardenticatena Kawaichi et al. 2013
* Order "Epilineales" Petriglieri et al. 2023
** Family "Epilineaceae" Petriglieri et al. 2023
*** Genus "Candidatus Avedoeria" Petriglieri et al. 2023
*** Genus "Candidatus Epilinea" Petriglieri et al. 2023
Class "Caldilineia" Oren, Parte & Garrity 2016 ex Cavalier-Smith 2020
* Order Caldilineales Yamada et al. 2006
** Family "Amarolineaceae" Andersen et al. 2019
*** Genus "Candidatus Amarolinea" Andersen et al. 2019
** Family Caldilineaceae Yamada et al. 2006
*** Genus Caldilinea Sekiguchi et al. 2003
*** Genus "Candidatus Fredericiella" Petriglieri et al. 2023
*** Genus Litorilinea Kale et al. 2013
Class Thermoflexia Dodsworth et al. 2014
* Order Thermoflexales Dodsworth et al. 2014
** Family "Roseilineaceae" Ward et al. 2021
*** Genus "Candidatus Brachythrix" Petriglieri et al. 2023
*** Genus "Candidatus Roseilinea" Thiel et al. 2016
** Family Thermoflexaceae Dodsworth et al. 2014
*** Genus Thermoflexus Dodsworth et al. 2014
Class "Thermofontia" corrig. Ward et al. 2018
* Order "Phototrophicales" Zheng et al. 2022
** Family "Phototrophicaceae" Zheng et al. 2022
*** Genus "Candidatus Flexicrinis" Petriglieri et al. 2023
*** Genus "Candidatus Flexifilum" Petriglieri et al. 2023
*** Genus "Phototrophicus" Zheng et al. 2022
Class "Anaerolineia" Oren, Parte & Garrity 2016
* Genus ?"Candidatus Defluviifilum" Nierychlo et al. 2019
* Family "Profundisolitariaceae" Mehrshad et al. 2018
** Genus ?"Candidatus Profundisolitarius" Mehrshad et al. 2018 (CL500-11)
* Order "Promineifilales" Chuvochina et al. 2023
** Family "Promineifilaceae" Chuvochina et al. 2023
*** Genus "Candidatus Hadersleviella" Petriglieri et al. 2023
*** Genus "Candidatus Leptofilum" Petriglieri et al. 2023
*** Genus "Candidatus Leptovillus" Petriglieri et al. 2023
*** Genus "Candidatus Promineifilum" corrig. McIlroy et al. 2016
*** Genus "Candidatus Trichofilum" Petriglieri et al. 2023
* Order Aggregatilineales Nakahara et al. 2019
** Family Aggregatilineaceae Nakahara et al. 2019
*** Genus Aggregatilinea Nakahara et al. 2019
* Order Anaerolineales Yamada et al. 2006
** Family "Villigracilaceae" Petriglieri et al. 2023
*** Genus "Candidatus Defluviilinea" Petriglieri et al. 2023
*** Genus "Candidatus Denitrolinea" Petriglieri et al. 2023
*** Genus "Desulfolinea" Van Vliet et al. 2020
*** Genus ?"Candidatus Manresella" Petriglieri et al. 2023
*** Genus "Candidatus Villigracilis" Nierychlo et al. 2019 ex Petriglieri et al. 2023
** Family Anaerolineaceae Yamada et al. 2006
*** Genus Anaerolinea Sekiguchi et al. 2003 emend. Yamada et al. 2006
*** Genus Bellilinea Yamada et al. 2007
*** Genus "Brevefilum" McIlroy et al. 2017
*** Genus "Candidatus Denitrolinea" Okubo et al. 2021
*** Genus Flexilinea Sun et al. 2015
*** Genus Levilinea Yamada et al. 2006
*** Genus Leptolinea Yamada et al. 2006
*** Genus Longilinea Yamada et al. 2007
*** Genus ?"Candidatus Mesolinea" Bedoya-Urrego & Alzate 2024
*** Genus Ornatilinea Podosokorskaya et al. 2013
*** Genus Pelolinea Imachi et al. 2014
*** Genus ?Thermomarinilinea Nunoura et al. 2013
*** Genus "Thermanaerothrix" Gregoire et al. 2011

## Etymology

The name Chloroflexi is a Neolatin nominative case masculine plural of Chloroflexus, which is the name of the first genus described. The noun is a combination of the Greek adjective chloros, -a, on (χλωρός, -ά, -όν), meaning "greenish-yellow," and the Latin masculine passive perfect participle flexus (of flecto), meaning "bent." The etymology is unrelated to chlorine, an element that was discovered in 1810 by Sir Humphry Davy and named after its pale green colour. Another phylum with the same root is Chlorobiota, whereas "Cyanobacteria" has the root cyanos (κύανος), meaning "blue-green."
Unlike some other phyla, there is no theme root in the name of genera of Chloroflexota, and in fact many genera beginning with "Chloro-" or ending in "-chloris" are either cyanobacteria or chlorobi.