Terrabacteria
Encyclopedia
Terrabacteria is a taxon
containing approximately two-thirds (6,157 sp.) of prokaryote
species, including those in the gram positive phyla (Actinobacteria
and Firmicutes
) as well as the phyla Cyanobacteria, Chloroflexi
, and Deinococcus-Thermus
.
It derives its name (terra = "land") from the evolutionary pressures of life on land. Terrabacteria possess important adaptations such as resistance to environmental hazards (e.g., desiccation, ultraviolet radiation, and high salinity) and oxygenic photosynthesis. Also, the unique properties of the cell wall in gram-positive taxa, which likely evolved in response to terrestrial conditions, have contributed toward pathogenicity in many species . These results now leave open the possibility that terrestrial adaptations may have played a larger role in prokaryote evolution than currently understood .
Terrabacteria was proposed in 2004 for Actinobacteria, Cyanobacteria, and Deinococccus-Thermus and was expanded later to include Firmicutes and Chloroflexi . Other phylogenetic analyses have supported the close relationships of these phyla. Most species of prokaryotes not placed in Terrabacteria were assigned to the taxon Hydrobacteria (3,203 sp.), in reference to the moist environment inferred for the common ancestor of those species. Terrabacteria and Hydrobacteria were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time . Together, Terrabacteria and Hydrobacteria form a large group containing 99% (9,360 sp.) of all Eubacteria, and placed in the taxon Selabacteria, in allusion to their phototrophic abilities (selas = light) .
Terrabacteria should not be confused with the recently-described taxon "Glidobacteria" , which includes only some members of Terrabacteria but excludes Firmicutes and Actinobacteria, and is not supported by molecular phylogenetic data .
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Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
containing approximately two-thirds (6,157 sp.) of prokaryote
Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...
species, including those in the gram positive phyla (Actinobacteria
Actinobacteria
Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria....
and Firmicutes
Firmicutes
The Firmicutes are a phylum of bacteria, most of which have Gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative...
) as well as the phyla Cyanobacteria, Chloroflexi
Chloroflexi
Chloroflexi is one of four 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....
, and Deinococcus-Thermus
Deinococcus-Thermus
The Deinococcus-Thermus are a small group of bacteria composed of cocci highly resistant to environmental hazards.There are two main groups.* The Deinococcales include two families, with three genera, Deinococcus and Truepera, the former with several species that are resistant to radiation; they...
.
It derives its name (terra = "land") from the evolutionary pressures of life on land. Terrabacteria possess important adaptations such as resistance to environmental hazards (e.g., desiccation, ultraviolet radiation, and high salinity) and oxygenic photosynthesis. Also, the unique properties of the cell wall in gram-positive taxa, which likely evolved in response to terrestrial conditions, have contributed toward pathogenicity in many species . These results now leave open the possibility that terrestrial adaptations may have played a larger role in prokaryote evolution than currently understood .
Terrabacteria was proposed in 2004 for Actinobacteria, Cyanobacteria, and Deinococccus-Thermus and was expanded later to include Firmicutes and Chloroflexi . Other phylogenetic analyses have supported the close relationships of these phyla. Most species of prokaryotes not placed in Terrabacteria were assigned to the taxon Hydrobacteria (3,203 sp.), in reference to the moist environment inferred for the common ancestor of those species. Terrabacteria and Hydrobacteria were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time . Together, Terrabacteria and Hydrobacteria form a large group containing 99% (9,360 sp.) of all Eubacteria, and placed in the taxon Selabacteria, in allusion to their phototrophic abilities (selas = light) .
Terrabacteria should not be confused with the recently-described taxon "Glidobacteria" , which includes only some members of Terrabacteria but excludes Firmicutes and Actinobacteria, and is not supported by molecular phylogenetic data .
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