Chloroflexia Gupta et al., 2013
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Abstract
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)Lewis, Charlton T. and Charles Short, A Latin Dictionary. Oxford: Clarendon Press, 1879. Online version at Perseus 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.
Taxonomy
The currently accepted taxonomy is as follows:
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.
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.
Taxonomy
The currently accepted taxonomy is as follows:
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.