Breviatea, commonly known as breviate amoebae, are a group of free-living, amitochondriate

protists A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...

with uncertain phylogenetic position. They are biflagellate, and can live in anaerobic (oxygen-free) environments. They are currently placed in the

Obazoa Obazoa is a proposed sister clade of Amoebozoa (which together form Amorphea). The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and Apusomonadidae, the group's three constituent clades. Determining the placement of Bre ...

clade. They likely do not possess vinculin proteins. Their metabolism relies on fermentative production of ATP as an adaptation to their low-oxygen environment. The lineage emerged roughly one billion years ago, at a time when the oxygen content of the Earth's oceans was low, and they thus developed anaerobic lifestyles. Together with Apusomonads, they are the closest relatives of the Opisthokonts, a group that includes animals and fungi.

Characteristics

Mitochondrion-related organelles

Mitochondrion-related organelles (MROs) are organelles that evolved from a degradation of ancestral, fully functional

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

. Among Breviatea, MROs are present in '' Pygsuia'', '' Breviata'' and '' Subulatomonas''. In the cells of ''Pygsuia'', for which the complete

transcriptome The transcriptome is the set of all RNA transcripts, including coding and non-coding, in an individual or a population of cells. The term can also sometimes be used to refer to all RNAs, or just mRNA, depending on the particular experiment. The ...

is known, there is a single smooth MRO that lacks a mitochondrial genome and most components of the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

. Of the

citric acid cycle The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...

enzymes, which are present in the mitochondria in other organisms, only two are present in ''Pygsuia'':

fumarase Fumarase (or fumarate hydratase) is an enzyme () that catalyzes the reversible Hydration reaction, hydration/Dehydration reaction, dehydration of fumarate to malate. Fumarase comes in two forms: mitochondrial and cytosolic. The mitochondrial iso ...

and

succinate dehydrogenase Succinate dehydrogenase (SDH) or succinate-coenzyme Q reductase (SQR) or respiratory complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates ...

. In contrast, ''Lenisia'' cells contain multiple MROs with

crista A crista (; : cristae) is a fold in the inner mitochondrial membrane, inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large a ...

Evolution

Breviatea is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of basal

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s. They are closely related to the apusomonads and the Opisthokonta supergroup, and together they compose the larger clade

, which is the sister group to

Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...

. Within Breviatea, the four known species are distributed into smaller clades of two species each: one uniting '' Breviata'' with '' Subulatomonas'', and one uniting '' Lenisia'' with '' Pygsuia''.

Taxonomy

History

The class Breviatea was created in 2004 by British protozoologist

Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...

to group a problematic taxon previously known as ''‘Mastigamoeba invertens’''. This organism, initially classified in the Archamoebae within phylum

, appeared to strongly diverge in

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

trees based on

ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

and had a structure very different from other Archamoebae. Because of these results, ''‘M. invertens’'' was separated into the order Breviatida, contained in the monotypic class Breviatea. The organism was eventually renamed '' Breviata anathema''. A family-level rank for these amoebae, Breviatidae, was formally described by the same author in 2013.

Classification

There are currently four accepted genera, each containing only one species. * '' Breviata'' ** '' Breviata anathema'' *'' Lenisia'' **'' Lenisia limosa'' *'' Pygsuia'' ** '' Pygsuia biforma'' *'' Subulatomonas'' ** '' Subulatomonas tetraspora''

References

{{Taxonbar, from=Q21446474 Obazoa