Pseudomonadati

The synonymous 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. Since 2024, the only validly published name for this group is kingdom Pseudomonadati (there used to be none, because no levels above phylum could exist in earlier versions of the Prokaryotic Code).{{cite journal |last1=Göker |first1=Markus |last2=Oren |first2=Aharon |date=22 January 2024 |title=Valid publication of names of two domains and seven kingdoms of prokaryotes |journal=International Journal of Systematic and Evolutionary Microbiology |volume=74 |issue=1 |doi=10.1099/ijsem.0.006242}}

"Gracilicutes," which was described in 1978 by Gibbons and Murray,{{cite journal |last1=Gibbons |first1=N. E. |last2=Murray |first2=R. G. E. |date=1 January 1978 |title=Proposals Concerning the Higher Taxa of Bacteria |journal=International Journal of Systematic Bacteriology |volume=28 |issue=1 |pages=1–6 |doi=10.1099/00207713-28-1-1 |doi-access=free}} is sometimes used in place of Pseudomonadati. However, "Gracilicutes" included Cyanobacteria (a member of Terrabacteria) and was not constructed under the now generally accepted three-domain system. More recently, a redefinition of "Gracilicutes" was proposed{{cite journal |last1=Cavalier-Smith |first1=Thomas |date=2006 |title=Rooting the tree of life by transition analyses |journal=Biology Direct |volume=1 |issue=1 |pages=19 |doi=10.1186/1745-6150-1-19 |pmc=1586193 |pmid=16834776 |doi-access=free}} 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.

Pseudomonadati and Terrabacteria were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time.

They include these superphyla and phyla: Acidobacteriota, Aquificota, Bdellovibrionota, Campylobacterota, Deferribacterota, Dependentiae, Desulfobacterota, Desulfuromonadota, Elusimicrobiota, FCB superphylum, Myxococcota, Nitrospirota, Proteobacteria, PVC superphylum, and Spirochaetota.{{cite journal |last1=Coleman |first1=Gareth A. |last2=Davín |first2=Adrián A. |last3=Mahendrarajah |first3=Tara A. |last4=Szánthó |first4=Lénárd L. |last5=Spang |first5=Anja |last6=Hugenholtz |first6=Philip |last7=Szöllősi |first7=Gergely J. |last8=Williams |first8=Tom A. |date=7 May 2021 |title=A rooted phylogeny resolves early bacterial evolution |url=https://research-information.bris.ac.uk/en/publications/51e9e402-36b7-47a6-91de-32b8cf7320d2 |journal=Science |volume=372 |issue=6542 |pages=eabe0511 |doi=10.1126/science.abe0511 |pmid=33958449 |s2cid=233872903 |hdl-access=free |hdl=1983/51e9e402-36b7-47a6-91de-32b8cf7320d2}}{{cite journal |last1=Léonard |first1=Raphaël R. |last2=Sauvage |first2=Eric |last3=Lupo |first3=Valérian |last4=Perrin |first4=Amandine |last5=Sirjacobs |first5=Damien |last6=Charlier |first6=Paulette |last7=Kerff |first7=Frédéric |last8=Baurain |first8=Denis |date=18 February 2022 |title=Was the Last Bacterial Common Ancestor a Monoderm after All? |journal=Genes |volume=13 |issue=2 |pages=376 |doi=10.3390/genes13020376 |pmc=8871954 |pmid=35205421 |doi-access=free}}

Some unrooted molecular phylogenetic analyses{{cite journal |last1=Hug |first1=Laura A. |last2=Baker |first2=Brett J. |last3=Anantharaman |first3=Karthik |last4=Brown |first4=Christopher T. |last5=Probst |first5=Alexander J. |last6=Castelle |first6=Cindy J. |last7=Butterfield |first7=Cristina N. |last8=Hernsdorf |first8=Alex W. |last9=Amano |first9=Yuki |last10=Ise |first10=Kotaro |last11=Suzuki |first11=Yohey |last12=Dudek |first12=Natasha |last13=Relman |first13=David A. |last14=Finstad |first14=Kari M. |last15=Amundson |first15=Ronald |date=May 2016 |title=A new view of the tree of life |journal=Nature Microbiology |volume=1 |issue=5 |pages=16048 |doi=10.1038/nmicrobiol.2016.48 |pmid=27572647 |s2cid=3833474 |doi-access=free |last16=Thomas |first16=Brian C. |last17=Banfield |first17=Jillian F.}}{{cite journal |last1=Zhu |first1=Qiyun |last2=Mai |first2=Uyen |last3=Pfeiffer |first3=Wayne |last4=Janssen |first4=Stefan |last5=Asnicar |first5=Francesco |last6=Sanders |first6=Jon G. |last7=Belda-Ferre |first7=Pedro |last8=Al-Ghalith |first8=Gabriel A. |last9=Kopylova |first9=Evguenia |last10=McDonald |first10=Daniel |last11=Kosciolek |first11=Tomasz |last12=Yin |first12=John B. |last13=Huang |first13=Shi |last14=Salam |first14=Nimaichand |last15=Jiao |first15=Jian-Yu |date=December 2019 |title=Phylogenomics of 10,575 genomes reveals evolutionary proximity between domains Bacteria and Archaea |journal=Nature Communications |volume=10 |issue=1 |pages=5477 |bibcode=2019NatCo..10.5477Z |doi=10.1038/s41467-019-13443-4 |pmc=6889312 |pmid=31792218 |last16=Wu |first16=Zijun |last17=Xu |first17=Zhenjiang Z. |last18=Cantrell |first18=Kalen |last19=Yang |first19=Yimeng |last20=Sayyari |first20=Erfan |last21=Rabiee |first21=Maryam |last22=Morton |first22=James T. |last23=Podell |first23=Sheila |last24=Knights |first24=Dan |last25=Li |first25=Wen-Jun |last26=Huttenhower |first26=Curtis |last27=Segata |first27=Nicola |last28=Smarr |first28=Larry |last29=Mirarab |first29=Siavash |last30=Knight |first30=Rob}} have not supported this dichotomy of Terrabacteria and Pseudomonadati, but the most recent genomic analyses, including those that have focused on rooting the tree, have found these two groups to be monophyletic.

Together, Pseudomonadati and Terrabacteria form a large group containing 97% of prokaryotes and 99% of all species of Bacteria known by 2009, and placed by Battistuzzi and Hedges in the proposed taxon Selabacteria, in allusion to their phototrophic abilities (selas = light).{{cite book |last1=Battistuzzi |first1=FU |title=The Timetree of Life |last2=Hedges |first2=SB |date=2009 |publisher=Oxford University Press |editor1-last=Hedges |editor1-first=SB |location=New York |pages=106–115 |chapter=Eubacteria |editor2-last=Kumar |editor2-first=S}} Currently, the bacterial phyla that are outside of Pseudomonadati + Terrabacteria, and thus justifying the taxon Selabacteria, are debated and may or may not include Fusobacteria.

The definition of two major divisions within the domain Bacteria, Pseudomonadati, and Terrabacteria, has come largely from rooted phylogenetic analyses of genomes. Unrooted analyses have not fully supported this division, drawing attention to the importance of rooted trees of life.

{{Gallery |mode=packed |align=center |height=480

|File:Timeline of life.png|alt1=A timetree redrawn showing the division of Hydrobacteria and Terrabacteria.|A timetree redrawn from Battistuzzi and Hedges (2009) shows the division of Hydrobacteria and Terrabacteria.}}

The two recent analyses of bacterial phylogeny both supported the division of Pseudomonadati and Terrabacteria. However, they interpreted the evolution of the cell wall differently, with one concluding that the last common ancestor of Bacteria was a monoderm (gram-positive bacteria) and the other concluding that it was a diderm (gram-negative bacteria). The following tree is redrawn from one of those two recent studies, showing the phylogeny of bacterial phyla and superphyla, with the position of Fusobacteria being unresolved and DST being the closest relative of Terrabacteria:

{{Gallery |mode=packed |align=center |height=480

|File:Bacterial phyla and superphyla.png|A phylogeny of bacterial phyla and superphyla according to Coleman et al. (2021). Hydrobacteria was referred to as "Gracilicutes" in that study.}}

{{Reflist}}

{{Bacteria classification}}

{{Bacteria}}

{{Taxonbar|from1=Q117225134}}

{{Authority Control}}

Category:Bacteria taxa

Category:Bacteriology

Category:Kingdoms (biology)

Category:Low-importance medicine articles