Hemimastix kukwesjijk
| Hemimastix kukwesjijk | ||||||||||||
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| Hemimastix kukwesjijk | ||||||||||||
| Eglit & Simpson , 2018 |
Hemimastix kukwesjijk is a species fromthe Spironemidae family . It is one of the few species of the Hemimastigophora, a basal line of development with an unclear position within the eukaryotes and the first described species of the group of which DNA sequence data are available.
features
Hemimastix kukwesjijk is a unicellular organism 16.5 to 20.5 micrometers in length. When viewed from above, it is somewhat flattened and oval with a section at the front end called the capitulum . A morphologically delimitable cell mouth ( cytostome ) is not developed. Extrusomes are present near the leading end . The cell body is enclosed in two flattened, yet somewhat spirally twisted in itself stiff wrapping elements, such cases are among the protists pellicle or theca called. Between these plates there remains a furrow-like depression, in each of which a number of mutually equal length flagella (or flagella sitting). In this species there are 17 to 19 flagella per row, of which the front 9 to 10 are close together, the following are further apart, each individually in a small recess. The flagella are relatively stiff in the kinship group and are moved as a whole from the base, they hardly allow the animal to swim in free water, but serve to move on soil particles and other surfaces. The flagella are anchored in the cell body with individual, remarkably short kinetides . Inside the cell, a large nucleus with a distinct nucleolus can be seen in the middle (sub-central) . Behind it sits a contractile vacuole .
Hemimastix kukwesjijk differs from Hemimastix amphikineta , which was first described in 1988 , the only other known species of the genus, in that it has significantly larger cells with more flagella per row.
Like the related species, the species must be kept in culture and reproduced in it for a while by simple cell division, but it cannot be cultivated in the long term. Data on the full life cycle are therefore not available.
Phylogeny and Kinship
The genus Hemimastix belongs to the Spironemidae family first described by Franz Theodor Doflein in 1916 (type species Spironema multiciliatum Klebs, 1893). The family comprises three genera, in addition to Spironema and Hemimastix , Stereonema with only one species. Fewer than ten species are known, almost all of which have only been found once or very rarely, but this is probably due to the fact that soil-dwelling flagellates are only examined by a handful of specialists worldwide become.
The Spiromenidae are the only Hemimastigophora family. This group was reorganized by Foissner and Blatterer in 1988 on the basis of morphological characteristics in the range of a trunk (phylum) for the very similar species Hemimastix amphikineta . Since the species was found several times, but could not be cultivated permanently, no DNA sequences could be obtained with the techniques of the time. A better classification in the system based on phylogenomic comparisons, i.e. based on the comparison of homologous DNA sequences, was therefore not possible. Sequence samples could now be obtained from Hemimastix kukwesjijk (and the as yet undescribed species of the genus Spironema , previously known as Spironema cf. multiciliatum ) using a newly developed technique. With this technique, known as single-cell transcriptomics , a single cell can be examined in a targeted manner, so that no prior propagation in culture is necessary.
During the investigation, the relationship of the genera Spironema and Hemimastix , and their classification in an independent line of development Hemimastigophora, was confirmed. The investigation revealed a very basic position for the group, as the sister group of the entire clade of Diaphoretickes as the most likely position. However, this result is still quite uncertain; alternatively, a position within the Diaphoretickes as a sister group to a clade from Sar and some smaller groups could not be ruled out. A sequence of an (unknown) organism that is only known from environmental DNA samples indicates that there must obviously be other, previously unknown representatives. The isolated position of the Hemimastigophora, which is suggested by this investigation, moves it into the vicinity of the roots of all known eukaryotes, so that it is important for the clarification of the question of how the primordial eukaryote was organized and looked. The authors therefore take the view that classification as a phylum does not do justice to this special position and call for an even higher ranking.
Finds
Individuals of the species was discovered by biologist Yana Eglit , Dalhousie University , in 2016 from a soil sample on the Bluff Wilderness Trail in the province of Nova Scotia , Canada , and is only known from there. On the other hand, numerous finds of the sister species Hemimastix amphikineta have already been found from several continents (Australia, South and Central America, as well as Gough Island, Antartica and Hawaii), but all of them are in the southern hemisphere. Hemimastix kukwesjijk could be kept in culture with the soil-living protist Spumella (a relative of Ochromonas from the group of golden brown algae without plastids, which feeds on bacteria hetereotrophically) as a food base. Together with Hemimastix kukwesjijk was undescribed, at the site a Spironema -Art discovered.
The peculiar species name was derived from an expression in the language of the Mi'kmaq , on whose settlement area the species was discovered. In its oral tradition, a kukwes is a hairy, ogre- like being. The name was chosen because of the hairy appearance of the species due to the flagella.
Literature and Sources
- Gordon Lax, Yana Eglit, Laura Eme, Erin M. Bertrand, Andrew J. Roger, Alastair GB Simpson (2018): Hemimastigophora is a novel supra-kingdom-level lineage of eukaryotes. Nature (online before print) doi: 10.1038 / s41586-018-0708-8 (the work contains the first description of Hemimastix kukwesjijk )
- Wilhelm Foissner & Hubert Blatterer (1988): The Hemimastigophora (Hemimastix amphikineta nov. Gen., Nov. Spec.), A New Protistan Phylum from Gondwanian Soils. European Journal of Protistology 23: 361-383.
- Ilse and Wilhelm Foissner (1993): Revision of the Family Spironemidae Doflein (Protista, Hemimastigophora), with Description of Two New Species, Spironema terricola N.Sp. and Stereonema geiseri NG, N. Sp. Journal of Eukaryotic Microbiology 40 (4): 422-438.
- Martin Kolisko, Vittorio Boscaro, Fabien Burki, Denis H. Lynn, Patrick J. Keeling (2014): Single-cell transcriptomics for microbial eukaryotes. Current Biology 24 (22): R1081-R1082 doi: 10.1016 / j.cub.2014.10.026