Rank Class | Scientific name Chloroflexia | |
 | ||
Similar Bacteria, Chloroflexus aurantiacus, Green sulfur bacteria, Heliobacteria, Purple sulfur bacteria | ||
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.
Contents
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.
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. 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.
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. 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 Chloroflexus genus, 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. 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.
Taxonomy
The currently accepted taxonomy is as follows:
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) 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 (dephlogisticated muriatic acid air) which was confirmed as such in 1810 by Sir Humphry Davy and named after its pale green colour.