Metamonad

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The metamonads are a large group of flagellate amitochondriate microscopic eukaryotes. They include the retortamonads, diplomonads, parabasalids, oxymonads, and a range of more poorly studied taxa, most of which are free-living flagellates. All metamonads are anaerobic (many being aerotolerant anaerobes), and most members of the four groups listed above are symbiotes or parasites of animals, as is the case with Giardia lamblia which causes diarrhea in mammals.[1]

Characteristics

A number of parabasalids and oxymonads are found in termite guts, and play an important role in breaking down the cellulose found in wood. Some other metamonads are parasites.

These flagellates are unusual in lacking aerobic mitochondria. Originally they were considered among the most primitive eukaryotes, diverging from the others before mitochondria appeared. However, they are now known to have lost aerobic mitochondria secondarily, and retain both organelles and nuclear genes derived ultimately from the mitochondrial endosymbiont genome. Mitochondrial relics include hydrogenosomes, which produce hydrogen (and make ATP), and small structures called mitosomes.

It now appears the Metamonada are, together with Malawimonas, sister clades of the Podiata.[2]

All of these groups have flagella or basal bodies in characteristic groups of four (or more, in parabasalids), which are often associated with the nucleus, forming a structure called a karyomastigont. In addition, genera such as Carpediemonas and Trimastix are now known to be close relatives of the retortamonad-diplomonad lineage and the oxymonads, respectively. Most of the closer relatives of the retortamonad-diplomonad lineage actually have two flagella and basal bodies.

Classification

The metamonads were thought to make up part of the Excavata, a proposed eukaryotic supergroup including flagellates with feeding grooves and their close relatives. Their relationships are uncertain,[3] and they do not always appear together on molecular trees. Current opinion is that Excavata is not a monophyletic group, but it might be paraphyletic.

Metamonada were once again proposed to be basal eukaryotes in 2018.[4]

A view of the metamonad taxonomy is:[5][6][7][8][9][10][11][12][13][14][15][16][17][18]

Evolution

Within Metamonada, two main branches are recovered in recent phylogenetic analyses. One branch contains the Parabasalia and the closely related anaeramoebae. The other branch contains two large groups: the Fornicata, which is closely related to barthelonids[13] and the recently isolated Skoliomonas;[14] and the Preaxostyla.[12]

A 2023 study found it likely that Metamonada is a paraphyletic group at the base of Eukaryota, meaning their anaerobic metabolism possibly represents the ancestral condition in eukaryotes (similar to what the Archezoa-Metakaryota hypothesis proposed) and that aerobic mitochondria might not have the same origin as hydrogenosomes.[1]

References

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  1. ^ a b Page Module:Citation/CS1/styles.css has no content.Al Jewari, Caesar; Baldauf, Sandra L. (2023-04-28). "An excavate root for the eukaryote tree of life". Science Advances. 9 (17) eade4973. Bibcode:2023SciA....9E4973A. doi:10.1126/sciadv.ade4973. ISSN 2375-2548. PMC 10146883. PMID 37115919.
  2. ^ Page Module:Citation/CS1/styles.css has no content.Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (2016-06-01). "187-gene phylogeny of protozoan phylum Amoebozoa reveals a new class (Cutosea) of deep-branching, ultrastructurally unique, enveloped marine Lobosa and clarifies amoeba evolution". Molecular Phylogenetics and Evolution. 99: 275–296. doi:10.1016/j.ympev.2016.03.023. PMID 27001604.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Cavalier-Smith T (November 2003). "The excavate protozoan phyla Metamonada Grassé emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa". Int. J. Syst. Evol. Microbiol. 53 (Pt 6): 1741–58. doi:10.1099/ijs.0.02548-0. PMID 14657102.
  4. ^ Page Module:Citation/CS1/styles.css has no content.Krishnan, Arunkumar; Burroughs, A. Max; Iyer, Lakshminarayan; Aravind, L. (2018). "Unexpected Evolution of Lesion-Recognition Modules in Eukaryotic NER and Kinetoplast DNA Dynamics Proteins from Bacterial Mobile Elements". iScience. 23 (9): 192–208. bioRxiv 10.1101/361121. doi:10.1016/j.isci.2018.10.017. PMC 6222260.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Adl, Sina M.; Bass, David; Lane, Christopher E.; Lukeš, Julius; Schoch, Conrad L.; Smirnov, Alexey; Agatha, Sabine; Berney, Cedric; Brown, Matthew W.; Burki, Fabien; Cárdenas, Paco; Čepička, Ivan; Chistyakova, Lyudmila; del Campo, Javier; Dunthorn, Micah (2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. ISSN 1550-7408. PMC 6492006. PMID 30257078.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Boscaro, Vittorio; James, Erick R.; Fiorito, Rebecca; del Campo, Javier; Scheffrahn, Rudolf H.; Keeling, Patrick J. (2024). "Updated classification of the phylum Parabasalia". Journal of Eukaryotic Microbiology. 71 (4) e13035. doi:10.1111/jeu.13035. hdl:10261/374507. ISSN 1550-7408.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Cavalier-Smith, Thomas (2013-05-01). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". European Journal of Protistology. 49 (2): 115–178. doi:10.1016/j.ejop.2012.06.001. ISSN 0932-4739.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Vargová, Romana; Hanousková, Pavla; Salamonová, Jana; Žihala, David; Silberman, Jeffrey D.; Eliáš, Marek; Čepička, Ivan (2022-05-19). "Evidence for an Independent Hydrogenosome-to-Mitosome Transition in the CL3 Lineage of Fornicates". Frontiers in Microbiology. 13. doi:10.3389/fmicb.2022.866459. ISSN 1664-302X. PMC 9161772. PMID 35663895.
  9. ^ Page Module:Citation/CS1/styles.css has no content.Jørgensen, Anders; Sterud, Erik (2007-04-18). "Phylogeny of Spironucleus (Eopharyngia: Diplomonadida: Hexamitinae)". Protist. 158 (2): 247–254. doi:10.1016/j.protis.2006.12.003. ISSN 1434-4610.
  10. ^ Page Module:Citation/CS1/styles.css has no content.Kolisko, Martin; Cepicka, Ivan; Hampl, Vladimir; Leigh, Jessica; Roger, Andrew J.; Kulda, Jaroslav; Simpson, Alastair GB; Flegr, Jaroslav (2008-07-15). "Molecular phylogeny of diplomonads and enteromonads based on SSU rRNA, alpha-tubulin and HSP90 genes: Implications for the evolutionary history of the double karyomastigont of diplomonads". BMC Evolutionary Biology. 8 (1): 205. doi:10.1186/1471-2148-8-205. ISSN 1471-2148. PMC 2496913. PMID 18627633.
  11. ^ Page Module:Citation/CS1/styles.css has no content.Martínez-Díaz, Rafael A.; Castro, Ana Teresa; Herrera, Silvia; Ponce, Francisco (2001). "First report of the genus Retortamonas (Sarcomastigophora: Retortamonadidae) in birds". Memórias do Instituto Oswaldo Cruz. 96: 961–963. doi:10.1590/S0074-02762001000700013. ISSN 0074-0276.
  12. ^ a b Page Module:Citation/CS1/styles.css has no content.Stairs, Courtney W.; Táborský, Petr; Salomaki, Eric D.; Kolisko, Martin; Pánek, Tomáš; Eme, Laura; Hradilová, Miluše; Vlček, Čestmír; Jerlström-Hultqvist, Jon; Roger, Andrew J.; Čepička, Ivan (2021-12-20). "Anaeramoebae are a divergent lineage of eukaryotes that shed light on the transition from anaerobic mitochondria to hydrogenosomes". Current Biology. 31 (24): 5605–5612.e5. doi:10.1016/j.cub.2021.10.010. ISSN 0960-9822. PMID 34710348.
  13. ^ a b Page Module:Citation/CS1/styles.css has no content.Yazaki, Euki; Kume, Keitaro; Shiratori, Takashi; Eglit, Yana; Tanifuji, Goro; Harada, Ryo; Simpson, Alastair G. B.; Ishida, Ken-ichiro; Hashimoto, Tetsuo; Inagaki, Yuji (2020-09-09). "Barthelonids represent a deep-branching metamonad clade with mitochondrion-related organelles predicted to generate no ATP". Proceedings of the Royal Society B: Biological Sciences. 287 (1934) 20201538. doi:10.1098/rspb.2020.1538. ISSN 0962-8452. PMC 7542792. PMID 32873198.
  14. ^ a b Page Module:Citation/CS1/styles.css has no content.Eglit, Yana; Williams, Shelby K.; Roger, Andrew J.; Simpson, Alastair G. B. (2024). "Characterization of Skoliomonas gen. nov., a haloalkaliphilic anaerobe related to barthelonids (Metamonada)". Journal of Eukaryotic Microbiology. 71 (6) e13048. doi:10.1111/jeu.13048. ISSN 1550-7408. PMC 11603281. PMID 39225178.
  15. ^ Page Module:Citation/CS1/styles.css has no content.Zhang, Qianqian; Táborský, Petr; Silberman, Jeffrey D.; Pánek, Tomáš; Čepička, Ivan; Simpson, Alastair G. B. (2015-09-01). "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.
  16. ^ Page Module:Citation/CS1/styles.css has no content.Cavalier-Smith, Thomas (2022-05-01). "Ciliary transition zone evolution and the root of the eukaryote tree: implications for opisthokont origin and classification of kingdoms Protozoa, Plantae, and Fungi". Protoplasma. 259 (3): 487–593. doi:10.1007/s00709-021-01665-7. ISSN 1615-6102. PMC 9010356. PMID 34940909.
  17. ^ Page Module:Citation/CS1/styles.css has no content.Poinar, George (2009-10-01). "Early Cretaceous protist flagellates (Parabasalia: Hypermastigia: Oxymonada) of cockroaches (Insecta: Blattaria) in Burmese amber". Cretaceous Research. 30 (5): 1066–1072. doi:10.1016/j.cretres.2009.03.008. ISSN 0195-6671.
  18. ^ Page Module:Citation/CS1/styles.css has no content.Shiratori, Takashi; Eglit, Yana; Yazaki, Euki; Inagaki, Yuji; Simpson, Alastair G. B. (2026-04-03). "Morphology, Ultrastructure, and Classification of Barthelonids (Metamonada Incertae Sedis): With Descriptions of Microbarthelona Gen. Nov., and Parabarthelona Gen. Nov". Journal of Eukaryotic Microbiology. 73 (3). doi:10.1111/jeu.70080. ISSN 1066-5234. PMC 13087550. PMID 41992732.

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