A bikont ("two flagella") is any of the

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

organisms classified in the group Bikonta. Many single-celled members of the group, and the presumed ancestor, have two

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

Enzymes

Another shared trait of bikonts is the fusion of two

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s into a single unit: the genes for

thymidylate synthase Thymidylate synthase (TS) () is an enzyme that catalyzes the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP). Thymidine is one of the nucleotides in DNA. With inhibition of TS, an imbalance of deoxynucleo ...

(TS) and

dihydrofolate reductase Dihydrofolate reductase, or DHFR, is an enzyme that reduces dihydrofolic acid to tetrahydrofolic acid, using NADPH as an electron donor, which can be converted to the kinds of tetrahydrofolate cofactors used in 1-carbon transfer chemistry. In ...

(DHFR) encode a single

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

with two functions. The genes are separately translated in

unikont Amorphea are members of a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta, which includes the Fungi, Animals and the Choanomonada, or Choanoflagellates. The taxonomic affinities of the ...

Relationships

Some research suggests that a unikont (a eukaryotic cell with a single flagellum) was the ancestor of opisthokonts (Animals, Fungi, and related forms) and

Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...

, and a bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata. Cavalier-Smith has suggested that

Apusozoa The Apusozoa are an Obazoa phylum comprising several genera of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the prese ...

, which are typically considered '' incertae sedis'', are in fact bikonts. Relationships within the bikonts are not yet clear. Cavalier-Smith has grouped the Excavata and Rhizaria into the

Cabozoa In the classification of eukaryotes (living organisms with a cell nucleus), Cabozoa was a taxon proposed by Cavalier-Smith. It was a putative clade comprising the Rhizaria and Excavata. More recent research tends to place the Rhizaria with the ...

and the Archaeplastida and Chromalveolata into the Corticata, but at least one other study has suggested that the Rhizaria and Chromalveolata form a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

. An alternative to the Unikont–Bikont division was suggested by Derelle ''et al.'' in 2015, where they proposed the

acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...

s Opimoda–Diphoda respectively, as substitutes to the older terms. The name Diphoda is formed from the letters of

DIscoba Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of fre ...

and

diaPHOretickes Diaphoretickes () is a major group of eukaryotic organisms, with over 400,000 species. The majority of the earth's biomass that carries out photosynthesis belongs to Diaphoretickes. Diaphoretickes includes: * Archaeplastida (comprising red alg ...

(shown in capitals).

Cladogram

A "classical" cladogram (data from 2012, 2015) is: However, a cladogram (data from 2015, 2016) with the root in Excavata is The corticates correspond roughly to the bikonts. While Haptophyta, Cryptophyta, Glaucophyta,

Rhodophyta Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

, the SAR supergroup and viridiplantae are usually considered

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

, Archaeplastida may be paraphyletic, and the mutual relationships between these phyla are still to be fully resolved. Recent reconstructions placed Archaeplastida and Hacrobia together in an "HA supergroup" or "AH supergroup", which was a sister clade to the SAR supergroup within the SAR/HA supergroup. However, this seems to have fallen out of favor as the monophyly of hacrobia has come under dispute.

Enzymes

Relationships

Cladogram

See also

References

Further reading