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21-533: Trichozoa is a group of excavates . "Fornicata" is a similar grouping, but it excludes Parabasalia . "Eopharyngia" is an even more narrow grouping, including Retortamonadida and Diplomonadida but not Carpediemonas . CavalierSmith, T (April 1997). "Amoeboflagellates and mitochondrial cristae in eukaryote evolution: Megasystematics of the new protozoan subkingdoms Eozoa and Neozoa". Archiv für Protistenkunde . 147 (3–4): 237–258. doi : 10.1016/S0003-9365(97)80051-6 . This Excavata -related article
42-484: A monophyletic group. Phylogenetic analyses often do not place malawimonads on the same branch as the other Excavata. Excavates were thought to include multiple groups: Euglenozoa and Heterolobosea (Percolozoa) or Eozoa (as named by Cavalier-Smith ) appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria (Superphylum Discicristata ). A close relationship has been shown between Discicristata and Jakobida ,
63-574: A majority of the mitochondrial genome was transferred to the nucleus; because of this, all hydrogenosomal proteins are imported to the organelle. However, a hydrogenosomal genome has been detected in the cockroach ciliate Nyctotherus ovalis , and the stramenopile Blastocystis . Due to the fact that many organisms have evolved to fit their anaerobic environments, a multitude of organisms have independently evolved hydrogenosomes or structures with similar functions. The similarity between Nyctotherus and Blastocystis , which are only distantly related,
84-421: A mitochondrial organelle in greatly modified form (e.g. a hydrogenosome or mitosome ). Among those with mitochondria, the mitochondrial cristae may be tubular, discoidal , or in some cases, laminar. Most excavates have two, four, or more flagella . Many have a conspicuous ventral feeding groove with a characteristic ultrastructure , supported by microtubules —the "excavated" appearance of this groove giving
105-485: A narrow longitudinal groove down one side of the cell. The ancyromonad groove is not used for "suspension feeding", unlike in "typical excavates" (e.g. malawimonads, jakobids, Trimastix , Carpediemonas , Kiperferlia , etc). Ancyromonads instead capture prokaryotes attached to surfaces. The phylogenetic placement of ancyromonads is poorly understood (in 2020), however some phylogenetic analyses place them as close relatives of malawimonads. The conventional explanation for
126-773: A phylogenetic tree with the metamonad Parabasalia as basal Eukaryotes. Discoba and the rest of the Eukaryota appear to have emerged as sister taxon to the Preaxostyla, incorporating a single alphaproteobacterium as mitochondria by endosymbiosis. Thus the Fornicata are more closely related to e.g. animals than to Parabasalia. The rest of the Eukaryotes emerged within the Excavata as sister of the Discoba; as they are within
147-516: Is a stub . You can help Misplaced Pages by expanding it . Excavata 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
168-517: Is believed to be the result of convergent evolution, and calls into question whether there is a clear-cut distinction between mitochondria, hydrogenosomes, and mitosomes (another kind of degenerate mitochondria). A non-exhaustive list of organisms containing hydrogenosomes includes: The vast variety of source organisms can be accredited to the theorized convergent evolution of hydrogenosomes from mitochondria to fit an anaerobic environment. In 2010, scientists have also reported their discovery of
189-436: The biochemical cytology and subcellular organization of several anaerobic protozoan parasites (ex: Trichomonas vaginalis , Tritrichomonas foetus , Giardia lamblia , and Entamoeba sp.) . Using information obtained from hydrogenosomal and biochemical cytology studies these researchers determined the mode of action of metronidazole (Flagyl) . Today, metronidazole is recognized as a standard chemotherapeutic agent for
210-459: The composition of the excavates is given below, indicating that the group is paraphyletic. Except for some Euglenozoa , all are non- photosynthetic . Most excavates are unicellular, heterotrophic flagellates. Only some Euglenozoa are photosynthetic. In some (particularly anaerobic intestinal parasites), the mitochondria have been greatly reduced. Some excavates lack "classical" mitochondria , and are called "amitochondriate", although most retain
231-550: The first known anaerobic metazoans with hydrogenosome-like organelles. Three multicellular species of Loricifera — Spinoloricus nov. sp. , Rugiloricus nov. sp. and Pliciloricus nov. sp. — have been found deep in Mediterranean sediments, and use hydrogenosomes in their anaerobic metabolism cycle. The hydrogenosomes of trichomonads (the most studied of the hydrogenosome-containing microorganisms) produce molecular hydrogen , acetate , carbon dioxide and ATP by
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#1732780767328252-745: The latter having tubular cristae like most other protists, and hence were united under the taxon name Discoba , which was proposed for this supposedly monophyletic group. Metamonads are unusual in not having classical mitochondria—instead they have hydrogenosomes , mitosomes or uncharacterised organelles. The oxymonad Monocercomonoides is reported to have completely lost homologous organelles. There are competing explanations. The malawimonads have been proposed to be members of Excavata owing to their typical excavate morphology, and phylogenetic affinity to other excavate groups in some molecular phylogenies. However, their position among eukaryotes remains elusive. Ancyromonads are small free-living cells with
273-451: The now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive ultrastructural identity ). They are considered to be a basal flagellate lineage. On the basis of phylogenomic analyses, the group was shown to contain three widely separated eukaryote groups, the discobids, metamonads, and malawimonads. A current view of
294-423: The organelle differs in various sources. Hydrogenosomes were isolated, purified, biochemically characterized and named in the early 1970s by Lindmark and Müller at Rockefeller University. In addition to this seminal study on hydrogenosomes, they also demonstrated for the first time the presence of pyruvate:ferredoxin oxido-reductase and hydrogenase in eukaryotes . Further studies were subsequently conducted on
315-496: The organisms their name. However, various groups that lack these traits are considered to be derived excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences). The Acrasidae slime molds are the only excavates to exhibit limited multicellularity. Like other cellular slime molds , they live most of their life as single cells, but will sometimes assemble into larger clusters. Excavate relationships were always uncertain, suggesting that they are not
336-439: The origin of the Eukaryotes is that a heimdallarchaeian or another Archaea acquired an alphaproteobacterium as an endosymbiont , and that this became the mitochondrion , the organelle providing oxidative respiration to the eukaryotic cell. Caesar al Jewari and Sandra Baldauf argue instead that the Eukaryotes possibly started with an endosymbiosis event of a Deltaproteobacterium or Gammaproteobacterium , accounting for
357-575: The otherwise unexplained presence of anaerobic bacterial enzymes in Metamonada. The sister of the Preaxostyla within Metamonada represents the rest of the Eukaryotes which acquired an Alphaproteobacterium. In their scenario, the hydrogenosome and mitosome , both conventionally considered "mitochondrion-derived organelles", would predate the mitochondrion, and instead be derived from the earlier symbiotic bacterium. In 2023, using molecular phylogenetic analysis of 186 taxa, Al Jewari and Baldauf proposed
378-405: The production of molecular hydrogen, from which the organelle receives its name. Hydrogenosomes range from 0.5-2 micrometers and are bound by a double membrane. They are most often dumb-bell-shaped and found in large complexes of stacked hydrogenosomes. These stacks range from 4 or 5 (called juvenile complexes) to 20 or more hydrogenosomes. In most cases, hydrogenosomes are genomeless , as
399-655: The root of a tree is often difficult to pinpoint. Metakaryota Hydrogenosome A hydrogenosome is a membrane -enclosed organelle found in some anaerobic ciliates , flagellates , and fungi . Hydrogenosomes are highly variable organelles that have presumably evolved from proto mitochondria to produce molecular hydrogen and ATP in anaerobic conditions. Hydrogenosomes were discovered in 1973 by D. G. Lindmark and M. Müller. Because hydrogenosomes hold evolutionary lineage significance for organisms living in anaerobic or oxygen-stressed environments, many research institutions have since documented their findings on how
420-425: The same clade but are not cladistically considered part of the Excavata yet, the Excavata are in this analysis highly paraphyletic. Hodarchaeales Parabasalia Fornicata Preaxostyla Jakobida Heterolobosea Euglenozoa and allies Amorphea (inc. animals, fungi) SAR Archaeplastida (inc. plants) The Anaeramoeba are associated with Parabasalia, but could turn out to be more basal as
441-433: The treatment of anaerobic infections. Since their discovery, hydrogenosomes have been found in a variety of anaerobic unicellular ciliates, flagellates, and fungi. The most notable amongst these is the parasitic Trichomonas vaginalis . Hydrogenosomes are organelles that are speculated to have evolved from mitochondria to provide a different mechanism for anaerobic ATP synthesis utilizing pyruvate. The reaction results in
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