Ancoracysta twista
| Ancoracysta twista | ||||||||||
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| Systematics | ||||||||||
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| Scientific name of the genus | ||||||||||
| Ancoracysta | ||||||||||
| Janouškovec et al., 2017 | ||||||||||
| Scientific name of the species | ||||||||||
| Ancoracysta twista | ||||||||||
| Janouškovec et al. , 2017 |
Ancoracysta twista is a flagellate species that was newly discovered and scientifically described in 2017 on the surface of a coral in a marine aquarium. The species is taxonomically completely isolated, with no known close relatives, in alarge group of eukaryotes known as Diaphoretickes . It is notable for the genome of its mitochondria , which has an unusual number of functional coding genes.
features
Ancoracysta twista is a unicellular organism with a cell length of about 10 micrometers. The cell is enclosed in a shell, called theca , of unknown composition, consisting of four separate layers , which is covered by an amorphous envelope ( glycocalyx ). The roughly egg-shaped unicellular organisms are highly mobile and able to change direction quickly when swimming. They are driven by two very differently designed flagella . At the front end of the cell there is a long, straight trailing flagella, basal covered with ciliated hairs ( mastigonema ), this can be put back on the dorsal side of the cell. The much shorter second flagella has a narrow flag, it is moved in a longitudinal furrow on the ventral side, with the flag side pointing towards the cell. The cell has a clearly recognizable cell mouth or cytostome from which a conspicuously large food vacuole can be pinched off, which is located near the rear end in the cytoplasm . Characteristic and not observed in this form in any other protist is a special organelle belonging to the extrusomes , which was named ancoracyst . It forms a vacuole with an amphorae-shaped base that contains seven cylindrical strands surrounding a central strand. The striped neck region is followed by a lid-like closure made of a plate with seven sectors. The ancoracyst is emptied to the outside, it is probably used to immobilize the victim when catching prey. The mitochondria of Ancoracysta have lamellar cristae .
Biology and way of life
Since the species was discovered in a saltwater aquarium owned by the Scripps Institution of Oceanography , California , its natural habitat is still unknown to this day. She lived there on the surface of a brain coral . Ancoracysta twista feeds predatory, the prey organism in the culture was the heterotrophic nanoflagellate Procryptobia sorokini , which feeds on bacteria. A culture of Ancoracysta itself exclusively with bacterial cells was not possible.
Phylogeny
Ancoracysta could not be assigned to any known group of flagellates on the basis of morphological characteristics. Even a phylogenomic analysis, in which homologous gene sequences are compared to determine the relationship, unexpectedly did not allow an assignment to a previously characterized group. This was especially true when using the ribosomal RNA , which is often used for this purpose . Only a more complex analysis, in which the transcriptome of 201 proteins was used, resulted in an evaluable position, which, however, was uncertain and, depending on the method used, not stable. The maximum likelihood method resulted in a position as a sister group of the haptophyta and the centrohelida combined. According to a later analysis (not yet peer-reviewed), a sister group relationship with the haptophyta alone would also be conceivable. Sina Adl and colleagues therefore presented the genus in their new Phylogeny of Eukaryotes (with a focus on protists) published in 2018 as having an uncertain position (incertae sedis) within the large group of Diaphoretickes.
The independent genome of the mitochondria of Ancoracysta proved to be particularly remarkable . It is considered certain that these organelles arose from the uptake of an originally independent and free-living, bacteria-like organism by the cell of a primordial eukaryote (which presumably belonged to the archaea) ( endosymbiont theory ). The organism that formed the mitochondrion lost most of its original genes because these were copied into the nuclear genome as a result of copying errors and were later lost to the mitochondrion. Organisms with very gene-rich mitochondria are therefore presumably very basic forms of life that should be arranged close to the root of the eukaryotic family tree. This picture has now been called into question by the discovery of Ancoracysta . Because a second group, which is also provided with many mitochondrial genes, the Jakobida belonging to the Excavata , are neither closely related to Ancoracysta , nor does the order of the genes correspond particularly well in detail. It is therefore now rather assumed that the mitochondrial gene loss does not have to occur once, but in many kinship lines independently of one another, with different sequences and speeds.
Literature and Sources
- Jan Janouškovec, Denis V. Tikhonenkov, Fabien Burki, Alexis T. Howe, Forest L. Rohwer, Alexander P. Mylnikov, Patrick J. Keeling (2017): A New Lineage of Eukaryotes Illuminates Early Mitochondrial Genome Reduction. Current Biology 27: 3717-3724. doi: 10.1016 / j.cub.2017.10.051
Individual evidence
- ↑ Jürgen FH Strassert, Mahwash Jamy, Alexander P. Mylnikov, Denis V. Tikhonenkov, Fabien Burki: New phylogenomic analysis of the enigmatic phylum Telonemia further resolves the eukaryote tree of life. BioRxiv preprint server, doi: 10.1101 / 403329
- ↑ Sina M. Adl et al. (2018): Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes. Journal of Eukaryotic Microbiology, online before print, doi: 10.1111 / jeu.12691 (open access)
Web links
- Top 10 new species 2018, by Eleanor Imster May 29, 2018.