Bacillati
| Bacillati | |
|---|---|
 | |
| Scanning electron micrograph of Actinomyces israelii (Actinomycetota) | |
Scientific classification  | |
| Domain: | Bacteria |
| Kingdom: | Bacillati (Gibbons & Murray 1978) Oren & Göker 2024 |
| Type genus | |
| Bacillus Cohn 1872 (Approved Lists 1980) | |
| Phyla | |
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| Synonyms | |
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Bacillati, is a kingdom containing approximately two-thirds of prokaryote species, including those in the gram positive phyla (Actinomycetota and Bacillota) as well as the phyla Cyanobacteriota and Chloroflexota. It was originally proposed under the name "Terrabacteria", referring to the commonalities of its members: the possession of important adaptations to life on land such as resistance to environmental hazards (e.g., desiccation, ultraviolet radiation, and high salinity) and oxygenic photosynthesis.
The unique properties of the cell wall in gram-positive taxa, which likely evolved in response to terrestrial conditions, have also contributed toward pathogenicity in many species. This suggests that terrestrial adaptations may have played a larger role in prokaryote evolution than currently understood.
The closest relatives of the Bacillati are the Pseudomonadati ("Hydrobacteria"), originally named in reference to the moist environment inferred for the common ancestor of those species. Bacillati and Pseudomonadati were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time. Together, Bacillati and Pseudomonadati form a large clade containing 97% of prokaryotes and 99% of all species of Bacteria known by 2009.