Chloroflexi (class)

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 & Molecular Signatures

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 Chloroflexus genus, 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]

Taxonomy

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

• Order Chloroflexales
  • Suborder Chloroflexineae
    • Family Chloroflexaceae Trüper 1976 emend. Gupta et al. 2013
      • Genus Chloroflexus Pierson and Castenholz 1974
        • C. aggregans Hanada et al. 1995
        • C. aurantiacus Pierson and Castenholz 1974
    • Family Oscillochloridaceae Keppen 2000 emend. Gupta et al. 2013
      • Genus Oscillochloris Gorlenko and Pivovarova 1989 emend. Keppen et al. 2000
        • O. chrysea Gorlenko and Pivovarova 1989
        • O. trichoides (ex Szafer) Gorlenko and Korotkov1989 emend. Keppen et al. 2000
      • Genus Chloronema Dubinina and Gorlenko 1975
        • Chloronema giganteum Dubinina and Gorlenko 1975
  • Suborder Roseiflexineae
    • Family Roseiflexaceae Gupta et al. 2013
      • Genus Roseiflexus Hanada et al. 2002
        • Roseiflexus castenholzii Hanada et al. 2002
      • Genus Heliothrix Pierson et al. 1986
        • Heliothrix oregonensis Pierson et al. 1986
• Order "Herpetosiphonales"
  • Family "Herpetosiphonaceae"
    • Genus Herpetosiphon Holt and Lewin 1968
      • H. aurantiacus Holt and Lewin 1968
      • H. geysericola (Copeland 1936) Lewin 1970

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

Etymology

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 (dephlogisticated muriatic acid air) which was confirmed as such in 1810 by Sir Humphry Davy and named after its pale green colour.

References

Further reading

• Garrity GM, Holt JG (2001). "Phylum BVI. Chloroflexi phy. nov". In D.R. Boone and R.W. Castenholz, eds. Bergey's Manual of Systematic Bacteriology Volume 1: The Archaea and the deeply branching and phototrophic Bacteria (2nd ed.). New York: Springer Verlag. p. 169. ISBN 978-0-387-98771-2.  CS1 maint: Uses editors parameter (link)

External links

• PubMed references for Chloroflexi
• PubMed Central references for Chloroflexi
• Google Scholar references for Chloroflexi

External links

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