biology

Pseudomonadati

Pseudomonadati is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pseudomonadati rather than just read about it. In short: Pseudomonadati is a prokaryotic kingdom containing approximately one-third of prokaryote species, mostly gram-negative bacteria and their relatives. The grouping was originally proposed under the name "Hydrobacteria".

Key takeaways

Pseudomonadati belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pseudomonadati to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pseudomonadati from memory before moving on to harder problems.

Reference excerpt

Pseudomonadati is a prokaryotic kingdom containing approximately one-third of prokaryote species, mostly gram-negative bacteria and their relatives. The grouping was originally proposed under the name "Hydrobacteria". Hydrobacteria is the closest relative of an even larger kingdom of Bacteria, the Bacillati ("Terrabacteria"), which are mostly gram-positive bacteria. Pseudomonadati and Bacillati were inferred to have diverged approximately 3 billion years ago, suggesting that land (continents) had been colonized by prokaryotes at that time.

Names The synonymous name "Hydrobacteria" (hydro = "water") refers to the moist environment inferred for the common ancestor of those species. In contrast, species of Bacillati ("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). "Gracilicutes," which was described in 1978 by Gibbons and Murray, is sometimes used in place of Pseudomonadati. However, "Gracilicutes" included Cyanobacteria (a member of Bacillati) and was not constructed under the now generally accepted three-domain system. More recently, a redefinition of "Gracilicutes" was proposed 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.

Phylogeny and taxonomy They include these superphyla and phyla: Acidobacteriota, Aquificota, Bdellovibrionota, Campylobacterota, Deferribacterota, Dependentiae, Desulfobacterota, Desulfuromonadota, Elusimicrobiota, FCB superphylum, Myxococcota, Nitrospirota, Proteobacteria, PVC superphylum, and Spirochaetota. Some unrooted molecular phylogenetic analyses have not supported this dichotomy of Bacillati 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 Bacillati form a large clade 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 (Greek σέλας = light). Currently, the bacterial phyla that are outside of Pseudomonadati + Bacillati, 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 Bacillati, 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.

The two recent analyses of bacterial phylogeny both supported the division of Pseudomonadati and Bacillati. 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 Bacillati:

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI).

Unassigned phyla:

"Canglongiota" Zhang et al. 2022 Fidelibacterota Katayama et al. 2024 [incl. "Neomarinimicrobiota" Rinke et al. 2013] "Heilongiota" Zhang et al. 2022 "Nitrosediminicolota" Zhao, Jorgensen & Babbin 2024 "Saltatorellota" Wiegand et al. 2019 "Tianyaibacteriota" corrig. Cui et al. 2021

See also List of bacterial orders List of bacteria genera

References

Illustrations

Worked examples

Example 1 — a first encounter with Pseudomonadati

Start with the simplest possible case. Write down what Pseudomonadati claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pseudomonadati before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pseudomonadati ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pseudomonadati

In research: Pseudomonadati appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pseudomonadati in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pseudomonadati is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bacteria taxa, Bacteriology, Kingdoms (biology), so understanding it makes those chapters shorter.
In everyday life: Look for Pseudomonadati outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pseudomonadati in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pseudomonadati means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pseudomonadati out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pseudomonadati in simple terms?

Why does Pseudomonadati matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pseudomonadati?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pseudomonadati.