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 ...
s.
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.
See also
*
Corticata
References
Further reading
*
*
*
Tree of Life Eukaryotes
{{Taxonbar, from=Q860203
Eukaryote unranked clades
Taxa named by Thomas Cavalier-Smith