The Chloroflexota are a phylum of bacteria largely described as green non-sulfur bacteria. The phylum contains classes with a diverse range of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photosynthesis; and anaerobic halorespirers, which uses halogenated organics (such as the toxic chlorinated ethenes and polychlorinated biphenyls) as electron acceptors.
The phylum consists of eight distinct classes: Anaerolinae, Ardenticatenia, Caldilineae, Chloroflexia, Dehalococcoidia, Ktedonobacteria, Tepidiformia and Thermoflexia.
The members of the phylum Chloroflexota are monoderms (that is, have one cell membrane with no outer membrane), but species stain both gram positive and 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) and Actinomycetota (high-G+C gram-positives).
History
The taxon name Chloroflexi 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. The phylum is now recognised as the Chloroflexota.
In 1987, Carl Woese, regarded as one of the forerunner of the molecular phylogeny revolution, had divided Eubacteria into 10 phyla based on 16S ribosomal RNA (SSU) sequences and grouped the genera Chloroflexus, Herpetosiphon and Thermomicrobium into the "green non-sulfur bacteria and relatives". The genera were placed in orders Chloroflexales and Herpetosiphonales, both placed in phylum Chloroflexi, and order Thermomicrobiales in phylum Thermomicrobia in Volume One of Bergey's Manual of Systematic Bacteriology.
Chloroflexi, being a deep branching phylum (see Bacterial phyla), 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 is now divided several classes.
"Dehalococcoidetes" was 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. This class is now recognised as Dehalococcoidia
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.
The LPSN currently recognise eight classees: Anaerolineae Yamada et al. 2006 Ardenticatenia Kawaichi et al. 2013 Caldilineae Yamada et al. 2006 Chloroflexia corrig. Gupta et al. 2013 (formerly class Chloroflexi) Dehalococcoidia Löffler et al. 2013 Ktedonobacteria corrig. Cavaletti et al. 2007 Tepidiformia Kochetkova et al. 2020 Thermoflexia Dodsworth et al. 2014
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 release 10-RS226
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 Ktedonobacteraceae corrig. Cavaletti et al. 2007 Genus Ktedonobacter corrig. Cavaletti et al. 2007 Genus Ktedonospora Yabe et al. 2021 Genus "Candidatus Paraktedonobacter" Roy et al. 2025 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 ?"Dehalobium" Wu et al. 2002 Genus ?"Candidatus Lithoflexus" Saghai et al. 2020 Genus ?"Candidatus Sarcinithrix" Nierychlo et al. 2019 Order "Chloroheliales" Tsuji et al. 2024 Family "Chloroheliaceae" Tsuji et al. 2024 Genus "Candidatus Chlorohelix" Tsuji et al. 2024 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 ?"Candidatus Amarofilum" Petriglieri et al. 2023 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