Chloroflexia

The Chloroflexia are a class of bacteria in the phylum Chloroflexota, 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 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.

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 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'' and '' Kallotenue'' species) that currently consist of three orders: Chloroflexales, Herpetosiphonales, and Kallotenuales. 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.

Microscopic distinguishing characteristics

Members of the phylum Chloroflexota are monoderms and stain mostly Gram negative, whereas most bacteria species are diderms and stain Gram negative, with the Gram positive exceptions of the Bacillota (low GC Gram positives), Actinomycetota (high GC, Gram positives), and the Deinococcota (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 (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, quinones, and fatty acid 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'' 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 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 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">Flavilitoribacter.html" ;"title="'Flavilitoribacter">'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 "''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'' 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

See also

* List of bacteria genera
* List of bacterial orders

References

Further reading

*

External links

*

External links

{{Taxonbar, from=Q15732012

Bergey's volume 1
Phototrophic bacteria