The Chloroflexia are a class of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

in the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

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 photo ...

, known as filamentous green non-sulfur bacteria. They use light for energy and are named for their green pigment, usually found in photosynthetic bodies called

chlorosome A chlorosome is a photosynthetic antenna complex found in green sulfur bacteria (GSB) and some green filamentous anoxygenic phototrophs (FAP) ( Chloroflexaceae, Oscillochloridaceae; both members of Chloroflexia). They differ from other antenna ...

s. Chloroflexia are typically filamentous, and can move about through

bacterial gliding Gliding motility is a type of translocation used by microorganisms that is independent of propulsive structures such as flagella, pili, and fimbriae. Gliding allows microorganisms to travel along the surface of low aqueous films. The mechanisms of ...

. They are facultatively

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cellu ...

, but do not produce oxygen in the process of producing energy from light, or

phototrophy Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconcep ...

. Additionally, Chloroflexia have a different method of phototrophy (

photoheterotroph Photoheterotrophs ('' Gk'': ''photo'' = light, ''hetero'' = (an)other, ''troph'' = nourishment) are heterotrophic phototrophs – that is, they are organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Cons ...

y) than true photosynthetic bacteria.

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) meaning "greenish-yellow" and the Latin ''flexus'' (of ''flecto'') meaning "bent" to mean "a green bending". The name is not due to chlorine, an element confirmed as such in 1810 by

Sir Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...

and named after its pale green colour.

Taxonomy and molecular signatures

The Chloroflexia class is a group of deep branching photosynthetic bacteria (with the exception of ''

Herpetosiphon ''Herpetosiphon'' is a genus of bacteria in the family ''Herpetosiphonaceae ''Herpetosiphonaceae'' is a family of bacteria in the order ''Herpetosiphonales Herpetosiphonales is an order of bacteria in the class Chloroflexia. See also * Li ...

'' and '' Kallotenue'' species) that currently consist of three orders:

Chloroflexales Chloroflexales is an order of bacteria in the class Chloroflexia. Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). * ...

Herpetosiphonales Herpetosiphonales is an order of bacteria in the class Chloroflexia. See also * List of bacterial orders This article lists the orders of the Bacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in N ...

, and Kallotenuales. The Herpetosiphonales and Kallotenuales each consist of a single genus within its own family,

Herpetosiphonaceae ''Herpetosiphonaceae'' is a family of bacteria in the order ''Herpetosiphonales Herpetosiphonales is an order of bacteria in the class Chloroflexia. See also * List of bacterial orders This article lists the orders of the Bacteria. The curre ...

(''

'') and Kallotenuaceae ('' Kallotenue''), respectively, whereas the

are more phylogenetically diverse.

Microscopic distinguishing characteristics

Members of the phylum

are

monoderm In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...

s and stain mostly Gram negative, whereas most bacteria species are

diderms Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall s ...

and stain

Gram negative The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

, with the Gram positive exceptions of the

Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the earl ...

(low GC Gram positives),

Actinomycetota The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soi ...

(high GC, Gram positives), and the

Deinococcota ''Deinococcota'' (synonym, ''Deinococcus-Thermus'') is a phylum of bacteria with a single class, ''Deinococci'', that are highly resistant to environmental hazards, also known as extremophiles. These bacteria have thick cell walls that give them ...

(Gram positive, diderms with thick peptidoglycan).

Genetic distinguishing characteristics

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''. The revised taxonomy was based on the identification of a number of

conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

(CSIs) which serve as highly reliable molecular markers of shared ancestry.

Physiological distinguishing characteristics

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 Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, ...

quinones The quinones are a class of organic compounds that are formally "derived from aromatic compounds uch as benzene or naphthalene">benzene.html" ;"title="uch as benzene">uch as benzene or naphthalene] by conversion of an even number of –CH= group ...

, and

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

profiles that are consistently absent in the other suborder. 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. Additional work has been done using CSIs to demarcate the phylogenetic position of ''Chloroflexia'' relative to neighbouring photosynthetic groups such as the Cyanobacteria. ''Chloroflexota'' species form a distinct lineage with ''

Chlorobiota The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthes ...

'' species, their closest phylogenetic relatives. A CSI has been found to be shared among both ''Chloroflexota'' and ''Chlorobiota'' members, which has been interpreted as the result of a

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...

event between the two relatives.

Phylogeny

Taxonomy

The currently accepted taxonomy is as follows: 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 " Thermobaculales" ** Family " Thermobaculaceae" *** Genus "'' Thermobaculum''" Botero et al. 2004 * Order Kallotenuales Cole et al. 2013 **F amily Kallotenuaceae Cole et al. 2013 *** Genus '' Kallotenue'' Cole et al. 2013 * Order

Gupta et al. 2013 ** Family

Gupta et al. 2013 *** Genus "''Candidatus'' Anthektikosiphon" Ward, Fischer & McGlynn 2020 *** Genus ''

'' Holt & Lewin 1968 'Flavilitoribacter'' García-López et al. 2020">Flavilitoribacter.html" ;"title="'Flavilitoribacter">'Flavilitoribacter'' García-López et al. 2020* Order

Gupta et al. 2013 ** Suborder Roseiflexineae Gupta et al. 2013 *** Family Roseiflexaceae Gupta et al. 2013 ["Kouleotrichaceae" Mehrshad et al. 2018] **** Genus "''Kouleothrix''" Kohno et al. 2002 **** Genus ''Heliothrix'' Pierson et al. 1986 **** 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 Chloroflexales is an order of bacteria in the class Chloroflexia. Taxonomy The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). * ...

'' Pierson & Castenholz 1974 ''Chlorocrinis''"">Chlorocrinis.html" ;"title="''Chlorocrinis">''Chlorocrinis''"*** Family Oscillochloridaceae Gupta et al. 2013 **** Genus ''Candidatus'' Chloroploca Gorlenko et al. 2014 **** Genus ''Chloronema'' ♪ Dubinina & Gorlenko 1975 **** Genus '' Oscillochloris'' Gorlenko & Pivovarova 1989 **** Genus ''Candidatus'' Viridilinea Grouzdev et al. 2018

References

External links

{{Taxonbar, from=Q15732012 Bergey's volume 1 Phototrophic bacteria

Etymology

Taxonomy and molecular signatures

Microscopic distinguishing characteristics

Genetic distinguishing characteristics

Physiological distinguishing characteristics

Phylogeny

Taxonomy

See also

References

Further reading

External links

External links