Chloroflexi (class)

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Scientific classification

Gupta et al. 2013
Orders & Suborders



Chloroflexia Castenholz 2001

The Chloroflexia are one of six classes of bacteria in the phylum Chloroflexi, known as filamentous green non-sulfur bacteria. They produce energy from light and are named for their green pigment, usually found in photosynthetic bodies called chlorosomes.

Chloroflexia are typically filamentous, and can move about through bacterial gliding. They are facultatively aerobic, but do not produce oxygen in the process of producing energy from light, or phototrophy. Additionally, Chloroflexia have a different method of phototrophy (photoheterotrophy) than true photosynthetic bacteria.

Whereas most bacteria, in terms of diversity, are diderms and stain Gram negative with the exception of the Firmicutes (low GC Gram positives), Actinobacteria (high GC, Gram positives) and the Deinococcus-Thermus group (Gram positive, but diderms with thick peptidoglycan), the members of the phylum Chloroflexi are monoderms and stain mostly Gram negative.[1][2][3]

Taxonomy and molecular signatures[edit]

The Chloroflexia class is a group of deep branching photosynthetic bacteria (with the exception of Herpetosiphon and Kallotenue species) that currently consist of three orders: Chloroflexales, Herpetosiphonales, and Kallotenuales.[4][5][6][7][8] The Herpetosiphonales and Kallotenuales each consist of a single genus within its own family, Herpetosiphonaceae (Herpetosiphon) and Kallotenuaceae (Kallotenue), respectively, whereas the Chloroflexales are more phylogenetically diverse.[4][5][7]

Comparative genomic analysis has recently refined the taxonomy of the class Chloroflexia, dividing the Chloroflexales into the suborder Chloroflexineae consisting of the families Oscillachloridaceae and Chloroflexaceae, and the suborder Roseiflexineae containing family Roseiflexaceae.[4] The revised taxonomy was based on the identification of a number of conserved signature indels (CSIs) which serve as highly reliable molecular markers of shared ancestry.[9][10][11][12] Additional support for the division of the Chloroflexales into two suborders is the observed differences in physiological characteristics where each suborder is characterized by distinct carotenoids, quinones, and fatty acid profiles that are consistently absent in the other suborder.[4][13][14] In addition to demarcating taxonomic ranks, CSIs may play a role in the unique characteristics of members within the clade. In particular, a four-amino-acid insert in the protein pyruvate flavodoxin/ferredoxin oxidoreductase, a protein which plays important roles in photosynthetic organisms, has been found exclusively among all members in the genus Chloroflexus, and is thought to play an important functional role.[15][16] Additional work has been done using CSIs to demarcate the phylogenetic position of Chloroflexia relative to neighbouring photosynthetic groups such as the Cyanobacteria.[17] Chloroflexia species form a distinct lineage with Chlorobi species, their closest phylogenetic relatives. A CSI has been found to be shared among both Chloroflexia and Chlorobi members, which has been interpreted as the result of a horizontal gene transfer event between the two relatives.[18]


The currently accepted taxonomy is as follows:[4][5][19]

Additionally, "Kouleothrix aurantiaca" and "Dehalobium chlorocoercia" have not been fully described.


The name "Chloroflexi" is a Neolatin plural of "Chloroflexus", which is the name of the first genus described. The noun is a combination of the Greek chloros (χλωρός)[20] meaning "greenish-yellow" and the Latin flexus (of flecto)[21] meaning "bent" to mean "a green bending".[22] The name is not due to chlorine, an element confirmed as such in 1810 by Sir Humphry Davy and named after its pale green colour.


  1. ^ Sutcliffe, I. C. (2010). "A phylum level perspective on bacterial cell envelope architecture". Trends in Microbiology. 18 (10): 464–470. doi:10.1016/j.tim.2010.06.005. PMID 20637628.
  2. ^ Campbell C, Sutcliffe IC, Gupta RS (2014). "Comparative proteome analysis of Acidaminococcus intestini supports a relationship between outer membrane biogenesis in Negativicutes and Proteobacteria" (PDF). Arch Microbiol. 196 (4): 307–310. doi:10.1007/s00203-014-0964-4. PMID 24535491.
  3. ^ Gupta RS (2003). "Evolutionary relationships among photosynthetic bacteria". Photosynth Res. 76 (1–3): 173–183. doi:10.1023/A:1024999314839. PMID 16228576.
  4. ^ a b c d e Gupta RS, Chander P, George S (2013). "Phylogenetic framework and molecular signatures for the class Chloroflexia and its different clades; proposal for division of the class Chloroflexia class. nov. [corrected] 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. PMID 22903492.
  5. ^ a b c Cole JK, Gieler BA, Heisler DL, Palisoc MM, Williams AJ, Dohnalkova AC, Ming H, Yu TT, Dodsworth JA, Li WJ, Hedlund BP (2013). "Kallotenue papyrolyticum gen. nov., sp. nov., a cellulolytic and filamentous thermophile that represents a novel lineage (Kallotenuales ord. nov., Kallotenuaceae fam. nov.) within the class Chloroflexia". Int J Syst Evol Microbiol. 63 (Pt 12): 4675–82. doi:10.1099/ijs.0.053348-0. PMID 23950149.
  6. ^ Gupta RS, Mukhtar T, Singh B (1999). "Evolutionary relationships among photosynthetic prokaryotes (Heliobacterium chlorum, Chloroflexus aurantiacus, cyanobacteria, Chlorobium tepidum and proteobacteria): implications regarding the origin of photosynthesis". Mol Microbiol. 32 (5): 893–906. doi:10.1046/j.1365-2958.1999.01417.x. PMID 10361294.
  7. ^ a b Sayers; et al. "Chloroflexia". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2016-10-25.
  8. ^ Euzeby J (2013). "List of new names and new combinations previously effectively, but not validly, published". Int. J. Syst. Evol. Microbiol. 63: 1577–1580. doi:10.1099/ijs.0.052571-0. PMC 5817221.
  9. ^ Gupta RS (2016). "Impact of genomics on the understanding of microbial evolution and classification: the importance of Darwin's views on classification". FEMS Microbiol Rev. 40 (4): 520–53. doi:10.1093/femsre/fuw011. PMID 27279642.
  10. ^ Gupta, R. S. (1998). "Protein phylogenies and signature sequences: A reappraisal of evolutionary relationships among archaebacteria, eubacteria, and eukaryotes". Microbiology and Molecular Biology Reviews. 62 (4): 1435–1491. PMC 98952. PMID 9841678.
  11. ^ Rokas, A.; Holland, P. W. (2000). "Rare genomic changes as a tool for phylogenetics". Trends in Ecology & Evolution. 15 (11): 454–459. doi:10.1016/S0169-5347(00)01967-4. PMID 11050348.
  12. ^ Gupta, R. S.; Griffiths, E. (2002). "Critical issues in bacterial phylogeny". Theoretical Population Biology. 61 (4): 423–434. doi:10.1006/tpbi.2002.1589. PMID 12167362.
  13. ^ Hanada S, Pierson BK (2006) The Family Chloroflexaceae. In: The prokaryotes: a handbook on the biology of bacteria, pp. 815-842. Eds Dworkin M, Falkow S, Rosenberg E, Schleifer KH, Stackebrandt E Springer-: New York.
  14. ^ Pierson BK, Castenholz RW (1992) The Family Chloroflexaceae. In: The prokaryotes, pp. 3754-3775. Eds Balows A, Truper HG, Dworkin M, Harder W, Schleifer KH Springer-: New York.
  15. ^ Gupta RS (2010). "Molecular signatures for the main phyla of photosynthetic bacteria and their subgroups". Photosynth Res. 104 (2–3): 357–372. doi:10.1007/s11120-010-9553-9. PMID 20414806.
  16. ^ Stolz, F. M.; Hansmann, I. (1990). "An MspI RFLP detected by probe pFMS76 D20S23 isolated from a flow-sorted chromosome 20-specific DNA library". Nucleic Acids Research. 18 (7): 1929. doi:10.1093/nar/18.7.1929. PMC 330654. PMID 1692410.
  17. ^ Khadka B, Adeolu M, Blankenship RE, Gupta RS (2016). "Novel insights into the origin and diversification of photosynthesis based on analyses of conserved indels in the core reaction center proteins". Photosynth Res. Epub ahead of print (2): 159–171. doi:10.1007/s11120-016-0307-1. PMID 27638319.
  18. ^ Gupta RS (2012). "Origin and spread of photosynthesis based upon conserved sequence features in key bacteriochlorophyll biosynthesis proteins". Mol Biol Evol. 29 (11): 3397–412. doi:10.1093/molbev/mss145. PMID 22628531.
  19. ^ Classification of Chloroflexi entry in LPSN [Euzéby, J.P. (1997). "List of Bacterial Names with Standing in Nomenclature: a folder available on the Internet". Int J Syst Bacteriol. Microbiology Society. 47 (2): 590–2. doi:10.1099/00207713-47-2-590. ISSN 0020-7713. PMID 9103655. Retrieved 2019-02-23.]
  20. ^ χλωρός. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
  21. ^ Lewis, Charlton T. and Charles Short, A Latin Dictionary. Oxford: Clarendon Press, 1879. Online version at Perseus
  22. ^ 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. 2A (2nd ed.). New York: Springer. p. 304. ISBN 978-0-387-24143-2. British Library no. GBA561951.

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