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Hydrobacteria
Clade of bacteria / From Wikipedia, the free encyclopedia
Hydrobacteria is a taxon containing approximately one-third of prokaryote species, mostly gram-negative bacteria and their relatives.[1] It was found to be the closest relative of an even larger group of Bacteria, Terrabacteria, which are mostly gram-positive bacteria.[2][1] The name Hydrobacteria (hydro = "water") refers to the moist environment inferred for the common ancestor of those species. In contrast, species of Terrabacteria possess adaptations for life on land.[2][1]
Hydrobacteria | |
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Escherichia coli cells magnified 25,000 times | |
Scientific classification ![]() | |
Domain: | Bacteria |
Clade: | Hydrobacteria Battistuzzi and Hedges 2009[1] |
Superphyla/Phyla | |
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The content of Hydrobacteria has grown to include these superphyla and phyla: Acidobacteriota, Aquificota, Bdellovibrionota, Campylobacterota, Deferribacterota, Dependentiae, Desulfobacterota, Desulfuromonadota, Elusimicrobiota, FCB superphylum, Myxococcota, Nitrospirota, Proteobacteria, PVC superphylum, and Spirochaetota.[3][4]
Some unrooted molecular phylogenetic analyses[5][6] have not supported this dichotomy of Terrabacteria and Hydrobacteria, but the most recent genomic analyses,[3][4] including those that have focused on rooting the tree,[3] have found these two groups to be monophyletic.
Hydrobacteria and Terrabacteria were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time.[1] Together, Hydrobacteria and Terrabacteria 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).[7] Currently, the bacterial phyla that are outside of Hydrobacteria + Terrabacteria, and thus justifying the taxon Selabacteria, are debated and may or may not include Fusobacteria.[3][4]
"Gracilicutes," which was described in 1978 by Gibbons and Murray,[8] is sometimes used in place of Hydrobacteria. However, "Gracilicutes" included cyanobacteria (a member of Terrabacteria) and was not constructed under the now generally accepted three-domain system.[8] More recently, a redefinition of "Gracilicutes" was proposed[9] but it did not include a molecular phylogeny or statistical analyses. Also, it did not follow the three-domain system, claiming instead that the lineage of eukaryotes + Archaea is nested within Bacteria as a close relative of Actinomycetota, a tree not supported in any molecular phylogeny.