| Kinetoplastida | |
|---|---|
 | |
| Trypanosoma cruzi parasites | |
Scientific classification | |
| Domain: | Eukaryota |
| Phylum: | Euglenozoa |
| Subphylum: | Glycomonada |
| Class: | Kinetoplastea Honigberg, 1963 emend. Cavalier-Smith, 1981[1][2] |
| Subdivisions | |
| Synonyms | |
| |
Kinetoplastida (orKinetoplastea, as aclass) is a group offlagellatedprotists belonging to thephylumEuglenozoa,[3][4] and characterised by the presence of a distinctiveorganelle called thekinetoplast (hence the name), a granule containing a large mass ofDNA. The group includes a number ofparasites responsible for serious diseases in humans and other animals, as well as various forms found in soil and aquatic environments. The organisms are commonly referred to as "kinetoplastids" or "kinetoplasts".[5]
The kinetoplastids were first defined byBronislaw M. Honigberg in 1963 as the members of the flagellated protozoans.[1] They are traditionally divided into the biflagellateBodonidae and uniflagellateTrypanosomatidae; the former appears to beparaphyletic to the latter. One family of kinetoplastids, the trypanosomatids, is notable as it includes several genera which are exclusively parasitic.Bodo is a typical genus within kinetoplastida, which also includes various common free-living species which feed onbacteria. Others includeCryptobia and the parasiticLeishmania.
Honigberg created the taxonomic names Kinetoplastida and Kinetoplastea in 1963.[1] Since then there is no consensus on the use of either of the two as a definitetaxon. Kinetoplastea is more widely used as the class,[6][7][8][9][10] while Kinetoplastida is mostly used to designate theorder,[4][11][12][13] but is also used as a class.[3][14]Lynn Margulis, who initially accepted Kinetoplastida as an order in 1974, later placed it as a class.[15] Use of Kinetoplastida as an order also creates confusion as there is already an older name Trypanosomatida Kent, 1880, under which the kinetoplastids are most often placed.[16]
Kinetoplastida is divided into two subclasses -Metakinetoplastina andProkinetoplastina.[17][18]
Kinetoplastids areeukaryotic and possess normal eukaryotic organelles, for example thenucleus, mitochondrion,golgi apparatus and flagellum. Along with these universal structures, kinetoplastids have several distinguishing morphological features such as the kinetoplast, sub-pellicular microtubule array and paraflagellar rod.[citation needed]
The kinetoplast, after which the class is named, is a dense DNA-containing granule within the cell's single mitochondrion, containing many copies of the mitochondrialgenome. The structure is made up of a network of concatenated circular DNA molecules and their related structural proteins along withDNA andRNA polymerases. The kinetoplast is found at the base of a cell's flagella and is associated to the flagellumbasal body by acytoskeletal structure.[citation needed]
The cytoskeleton of kinetoplastids is primarily made up ofmicrotubules. These make a highly regular array, the sub-pellicular array, which runs parallel just under the cell surface along the long axis of the cell. Other microtubules with more specialised roles, such as therootlet microtubules, are also present. Kinetoplastids are capable of formingactinmicrofilaments but their role in the cytoskeleton is not clear. Other cytoskeletal structures include the specialised attachment between the flagellum and the kinetoplast.[citation needed]
All kinetoplastids possess at least one flagellum; species in the order trypanosomatida have one andbodonida have two. In kinetoplastids with two flagella most forms have a leading and trailing flagellum, the latter of which may be attached to the side of the cell. The flagella are used for locomotion and attachment to surfaces. The bases of the flagella are found in a specialised pocket structure which is also the location of thecytostome.[citation needed]
Kinetoplastids may be free-living or parasitic. The order trypanosomatida is notable as it includes many genera which are exclusively parasitic. Trypanosomatids may have simple life cycles in a single host or more complex ones which progress through multiple differentiation stages in two hosts. Dramatic morphological changes are possible between lifecycle stages. Diseases caused by members of the order trypanosomatida includesleeping sickness andChagas disease, caused by species ofTrypanosoma, andleishmaniasis, caused by species ofLeishmania.[19]
Trypanosoma brucei can undergomeiosis as a likely part of a sexual cycle.[20][21]Leishmania major is also capable of a meiotic process that is likely part of a sexual cycle.[22]
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