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 aerobicthermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photosynthesis; and anaerobichalorespirers, 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 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).
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.
Genus "CandidatusCaldibacter" corrig. Spieck et al. 2020
Genus "CandidatusChlorotrichoides" corrig. Oren et al. 2020 ["CandidatusChlorothrix" Klappenbach & Pierson 2004 non Dyar 1921 non Berger-Perrot 1982]
Genus "CandidatusNitrocaldera" Spieck et al. 2020
Genus "CandidatusNitrotheca" Spieck et al. 2020
Class "Bathosphaeria" Mehrshad et al. 2018
Order "Bathosphaerales" Mehrshad et al. 2018
Family "Bathosphaeraceae" Mehrshad et al. 2018
Genus?"CandidatusBathosphaera" Mehrshad et al. 2018 (JG30-KF-CM66)
Genus?"CandidatusTricholinea" Petriglieri et al. 2023
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.
↑Don J. Brenner; Noel R. Krieg; James T. Staley (July 26, 2005) [1984(Williams & Wilkins)]. George M. Garrity (ed.). Introductory Essays. Bergey's Manual of Systematic Bacteriology. Vol.2A (2nded.). New York: Springer. p.304. ISBN978-0-387-24143-2. British Library no. GBA561951.
123Don J. Brenner; Noel R. Krieg; James T. Staley (July 26, 2005) [1984(Williams & Wilkins)]. George M. Garrity (ed.). Introductory Essays. Bergey's Manual of Systematic Bacteriology. Vol.2A (2nded.). New York: Springer. p.304. ISBN978-0-387-24143-2. British Library no. GBA561951.
12345Gupta, R. S.; Chander, P.; George, S. (2012). "Phylogenetic framework and molecular signatures for the class Chloroflexi and its different clades; proposal for division of the class Chloroflexi class. nov. into the suborder Chloroflexineae subord. nov., consisting of the emended family Oscillochloridaceae and the family Chloroflexaceae fam. nov., and the suborder Roseiflexineae subord. nov., containing the family Roseiflexaceae fam. nov". Antonie van Leeuwenhoek. 103 (1): 99–119. doi:10.1007/s10482-012-9790-3. PMID22903492. S2CID17656551.
↑Maymo-Gatell, X.; Chien, Y.; Gossett, J. M.; Zinder, S. H. (1997). "Isolation of a Bacterium That Reductively Dechlorinates Tetrachloroethene to Ethene". Science. 276 (5318): 1568–1571. doi:10.1126/science.276.5318.1568. PMID9171062.
↑"Dehalococcoidia Löffler et al. 2013". LPSN - List of Prokaryotic names with Standing in Nomenclature. Leibniz Institute DSMZ. Retrieved 4 October 2026.
↑Klappenbach, J. A.; Pierson, B. K. (2004). "Phylogenetic and physiological characterization of a filamentous anoxygenic photoautotrophic bacterium 'Candidatus Chlorothrix halophila' Gen. Nov., sp. Nov., recovered from hypersaline microbial mats". Archives of Microbiology. 181 (1): 17–25. Bibcode:2004ArMic.181...17K. doi:10.1007/s00203-003-0615-7. PMID14655000. S2CID23854988.
↑Grégoire, P.; Fardeau, M. L.; Joseph, M.; Guasco, S.; Hamaide, F.; Biasutti, S.; Michotey, V. R.; Bonin, P.; Ollivier, B. (2011). "Isolation and characterization of Thermanaerothrix daxensis gen. nov., sp. nov., a thermophilic anaerobic bacterium pertaining to the phylum "Chloroflexi", isolated from a deep hot aquifer in the Aquitaine Basin". Systematic and Applied Microbiology. 34 (7): 494–497. Bibcode:2011SyApM..34..494G. doi:10.1016/j.syapm.2011.02.004. PMID21621938.
