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A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, the term "flagellate" is included in other terms which are more formally characterized.
Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.
Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.
The metamonads are a large group of flagellate amitochondriate microscopic eukaryotes. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. These four groups are all anaerobic, occurring mostly as symbiotes or parasites of animals, as is the case with Giardia lamblia which causes diarrhea in mammals.
Amorphea is 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 members of this clade were originally described and proposed by Thomas Cavalier-Smith in 2002.
The Oxymonads are a group of flagellated protists found exclusively in the intestines of animals, mostly termites and other wood-eating insects. Along with the similar parabasalid flagellates, they harbor the symbiotic bacteria that are responsible for breaking down cellulose. There is no evidence for presence of mitochondria in oxymonads and 3 species have been shown to completely lack any molecular markers of mitochondria.
Discosea is a class of Amoebozoa, consisting of naked amoebae with a flattened, discoid body shape. Members of the group do not produce tubular or subcylindrical pseudopodia, like amoebae of the class Tubulinea. When a discosean is in motion, a transparent layer called hyaloplasm forms at the leading edge of the cell. In some discoseans, short "subpseudopodia" may be extended from this hyaloplasm, but the granular contents of the cell do not flow into these, as in true pseudopodia. Discosean amoebae lack hard shells, but some, like Cochliopodium and Korotnevella secrete intricate organic scales which may cover the upper (dorsal) surface of the cell. No species have flagella or flagellated stages of life.
A symbiotic eukaryote that lives in the hindgut of termites, Streblomastix is a protist associated with a community of ectosymbiotic bacteria.
Breviata anathema is a single-celled flagellate amoeboid eukaryote, previously studied under the name Mastigamoeba invertens. The cell lacks mitochondria, much like the pelobionts to which the species was previously assigned, but has remnant mitochondrial genes, and possesses an organelle believed to be a modified anaerobic mitochondrion, similar to the mitosomes and hydrogenosomes found in other eukaryotes that live in low-oxygen environments.
Trimastix is a genus of excavate protists, the sole occupant of the order Trimastigida. Trimastix are bacterivorous, free living and anaerobic. It was first observed in 1881 by William Kent. There are few known species, and the genus's role in the ecosystem is largely unknown. However, it is known that they generally live in marine environments within the tissues of decaying organisms to maintain an anoxic environment. Much interest in this group is related to its close association with other members of Preaxostyla. These organisms do not have classical mitochondria, and as such, much of the research involving these microbes is aimed at investigating the evolution of mitochondria.
Anaeromonadea, also known as Preaxostyla, is a class of excavate protists, comprising the oxymonads, Trimastix, and Paratrimastix. This group is studied as a model system for reductive evolution of mitochondria, because it includes both organisms with anaerobic mitochondrion-like organelles, and those that have completely lost their mitochondria.
Thecofilosea is a class of unicellular testate amoebae belonging to the phylum Cercozoa. They are amoeboflagellates, organisms with flagella and pseudopodia, distinguished from other cercozoa by their scale-lacking test composed of organic material. They are closely related to the Imbricatea, a group of testate amoebae with tests composed of inorganic silica scales.
Katablepharis is a genus of single-celled eukaryotes comprising five to six species. They are heterotrophic and live in both freshwater and seawater. They have two flagella and a feeding apparatus consisting of a mouth and two arrays of microtubules.
Mastigamoeba is a genus of pelobionts, and treated by some as members of the Archamoebae group of protists. Mastigamoeba are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage is as an amoeboid flagellate. Species are typically free living, though endobiotic species have been described.
The sarcomonads or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or external theca, a soft cell surface without obvious cortical filamentous or membranous skeleton, two cilia without scales or hairs, tubular mitochondrial cristae, near-spherical extrusomes, and a microbody attached to the nucleus.
Monocercomonoides is a genus of flagellate Excavata belonging to the order Oxymonadida. It was established by Bernard V. Travis and was first described as those with "polymastiginid flagellates having three anterior flagella and a trailing one originating at a single basal granule located in front of the anteriorly positioned nucleus, and a more or less well-defined axostyle". It is the first eukaryotic genus to be found to completely lack mitochondria, and all hallmark proteins responsible for mitochondrial function. The genus also lacks any other mitochondria related organelles (MROs) such as hydrogenosomes or mitosomes. Data suggests that the absence of mitochondria is not an ancestral feature, but rather due to secondary loss. Monocercomonoides sp. was found to obtain energy through an enzymatic action of nutrients absorbed from the environment. The genus has replaced the iron-sulfur cluster assembly pathway with a cytosolic sulfur mobilization system, likely acquired by horizontal gene transfer from a eubacterium of a common ancestor of oxymonads. These organisms are significant because they undermine assumptions that eukaryotes must have mitochondria to properly function. The genome of Monocercomonoides exilis has approximately 82 million base pairs, with 18 152 predicted protein-coding genes.
Platysulcus tardus is an eukaryotic microorganism that was recently discovered to be the earliest diverging lineage of the Heterokont phylogenetic tree. It is the only member of the family Platysulcidae, order Platysulcida and class Platysulcea.
Anaeramoeba is a genus of anaerobic protists of uncertain phylogenetic position, first described in 2016.
Helkesida is a group of microscopic protists belonging to the supergroup Rhizaria, both discovered through molecular phylogenetic analyses. It contains amoeboid flagellates with two flagella. They are either free-living, mostly on fecal matter, or live inside the gut of animals. Among these amoebae, one lineage has independently evolved aggregative multicellularity similarly to slime moulds.
Paratrimastix pyriformis is a species of free-living anaerobic freshwater bacteriovorous flagellated protists formerly known as Trimastix pyriformis and Tetramitus pyriformis.
References
- ↑ Zhang, Qianqian; Táborský, Petr; Silberman, Jeffrey D.; Pánek, Tomáš; Čepička, Ivan; Simpson, Alastair G.B. (September 2015). "Marine Isolates of Trimastix marina Form a Plesiomorphic Deep-branching Lineage within Preaxostyla, Separate from Other Known Trimastigids (Paratrimastix n. gen.)". Protist. 166 (4): 468–491. doi:10.1016/j.protis.2015.07.003. ISSN 1434-4610. PMID 26312987.
- ↑ O’Kelly, Charles J.; Farmer, Mark A.; Nerad, Thomas A. (August 1999). "Ultrastructure of Trimastix pyriformis (Klebs) Bernard et al.: Similarities of Trimastix Species with Retortamonad and Jakobid Flagellates". Protist. 150 (2): 149–162. doi:10.1016/S1434-4610(99)70018-0. PMID 10505415.
- ↑ Stechmann, Alexandra; Baumgartner, Manuela; Silberman, Jeffrey D; Roger, Andrew J (2006). "The glycolytic pathway of Trimastix pyriformis is an evolutionary mosaic". BMC Evolutionary Biology. 6 (1): 101. doi: 10.1186/1471-2148-6-101 . PMC 1665464 . PMID 17123440.
- ↑ Zubáčová, Zuzana; Novák, Lukáš; Bublíková, Jitka; Vacek, Vojtěch; Fousek, Jan; Rídl, Jakub; Tachezy, Jan; Doležal, Pavel; Vlček, Čestmír; Hampl, Vladimír (2013-03-13). Saks, Valdur (ed.). "The Mitochondrion-Like Organelle of Trimastix pyriformis Contains the Complete Glycine Cleavage System". PLOS ONE. 8 (3): e55417. Bibcode:2013PLoSO...855417Z. doi: 10.1371/journal.pone.0055417 . ISSN 1932-6203. PMC 3596361 . PMID 23516392.
- ↑ Zítek, Justyna; Füssy, Zoltán; Treitli, Sebastian C.; Peña-Diaz, Priscila; Vaitová, Zuzana; Zavadska, Daryna; Harant, Karel; Hampl, Vladimír (December 2022). "Reduced mitochondria provide an essential function for the cytosolic methionine cycle". Current Biology. 32 (23): 5057–5068.e5. Bibcode:2022CBio...32E5057Z. doi:10.1016/j.cub.2022.10.028. ISSN 0960-9822. PMC 9746703 . PMID 36347252.
- ↑ Zítek, Justyna; King, Martin S.; Peña-Diaz, Priscila; Pyrihová, Eva; King, Alannah C.; Kunji, Edmund R.S.; Hampl, Vladimír (July 2023). "The free-living flagellate Paratrimastix pyriformis uses a distinct mitochondrial carrier to balance adenine nucleotide pools". Archives of Biochemistry and Biophysics. 742: 109638. doi:10.1016/j.abb.2023.109638. PMC 10251735 . PMID 37192692.
- ↑ Novák, Lukáš V. F.; Treitli, Sebastian C.; Pyrih, Jan; Hałakuc, Paweł; Pipaliya, Shweta V.; Vacek, Vojtěch; Brzoň, Ondřej; Soukal, Petr; Eme, Laura; Dacks, Joel B.; Karnkowska, Anna; Eliáš, Marek; Hampl, Vladimír (2023-12-07). Dutcher, Susan K. (ed.). "Genomics of Preaxostyla Flagellates Illuminates the Path Towards the Loss of Mitochondria". PLOS Genetics. 19 (12): e1011050. doi: 10.1371/journal.pgen.1011050 . ISSN 1553-7404. PMC 10703272 . PMID 38060519.