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Terrabacteria is a
Recent molecular analyses have found roughly the following relationships including other phyla, whose relationships were uncertain.
On the other hand, Coleman et al. named the clade composed of Thermotogota,
taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
containing approximately two-thirds of prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Con ...
species, including those in the gram positive phyla (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 s ...
and 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 ...
) as well as the phyla "Cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
", 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 p ...
, and 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 ...
.
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
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. 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 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 s ...
, "Cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
", and 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 ...
and was expanded later to include 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 ...
and 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 p ...
. 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, in reference to the moist environment inferred for the common ancestor of those species. Some molecular phylogenetic analyses have not supported this dichotomy of Terrabacteria and Hydrobacteria, but the most recent genomic analyses, including those that have focused on rooting the tree, have found these two groups to be monophyletic.
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 97% of prokaryotes and 99% of all species of Bacteria known by 2009, and placed in the taxon Selabacteria, in allusion to their phototrophic abilities (''selas'' = light). Currently, the bacterial phyla that are outside of Terrabacteria + Hydrobacteria, and thus justifying the taxon Selabacteria, are debated and may or may not include Fusobacteria.
The name “Glidobacteria” included some members of Terrabacteria but excluded the large gram positive groups, 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 ...
and 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 s ...
, and is not supported by molecular phylogenetic data. Moreover, the article naming Glidobacteria did not include a molecular phylogeny or statistical analyses and did not follow the widely-used three-domain system
The three-domain system is a biological classification introduced by Carl Woese, Otto Kandler, and Mark Wheelis in 1990 that divides cellular life forms into three domains, namely Archaea, Bacteria, and Eukaryota or Eukarya. The key difference ...
. For example, it claimed that eukaryotes split from Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
very recently (~900 Mya), which is contradicted by the fossil record, and that lineage of eukaryotes + Archaea was nested within Bacteria as a close relative of 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 s ...
.
Phylogeny
The phylogenetic tree according to the phylogenetic analyses of Battistuzzi and Hedges (2009) is the following and with amolecular clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...
calibration.
Recent molecular analyses have found roughly the following relationships including other phyla, whose relationships were uncertain.
On the other hand, Coleman et al. named the clade composed of Thermotogota, 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 ...
, Synergistota and related as DST and furthermore the analysis suggests that ultra-small bacteria (CPR group) may belong to Terrabacteria being more closely related to 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 p ...
. According to this study the phylum Aquificota sometimes included belongs to Hydrobacteria and that the phylum Fusobacteriota can belong to both Terrabacteria and Hydrobacteria. The result was the following:
References
{{Taxonbar, from=Q873914 Bacterial nomenclature