Parabasalid

Parabasalid
Two trophozoites of Trichomonas vaginalis stained with Giemsa
Scientific classification
Domain:	Eukaryota
Phylum:	Metamonada
Subphylum:	Trichozoa
Clade:	Parabasalia Honigberg 1973
Orders [1]
Trichomonadida Cristamonadida Spirotrichonymphida Trichonymphida

The parabasalids are a group of flagellated protists within the supergroup Excavata. Most of these eukaryotic organisms form a symbiotic relationship in animals. These include a variety of forms found in the intestines of termites ^[2] and cockroaches, many of which have symbiotic bacteria that help them digest cellulose in woody plants. Other species within this supergroup are known parasites, and include human pathogens. ^{[3] [4]}

Characteristics

The flagella are arranged in one or more clusters near the anterior of the cell. Their basal bodies are linked to parabasal fibers that are associated with a prominent Golgi complex, together forming a parabasal apparatus distinctive to the group. ^[5] Attachment of a parabasal fiber to the first Golgi cisterna by thin filaments has been reported in Tritrichomonas foetus . ^[6] Usually they also give rise to a sheet of cross-like microtubules that runs down the center of the cell and in some cases projects past the end. This is called the axostyle, but is different in structure from the axostyles of oxymonads.^{[ citation needed ]}

Parabasalids are anaerobic, and lack mitochondria, but this is now known to be a result of secondary loss, and they contain small hydrogenosomes which apparently developed from reduced mitochondria. ^[7] Similar relics have been found in other amitochondriate flagellates, and the parabasalids are probably related to them, forming a group called the metamonads. They lack the feeding grooves found in most others, but this is probably a secondary loss as well.^{[ citation needed ]}

Representation of a Parabasalid

1. Anterior flagellum
2. Recurrent flagellum
3. Undulating membrane
4. Basal bodies
5. Golgi apparatus; modifies proteins and sends them out of the cell
6. Nucleus
7. Costa, a striated fiber associated with the undulating membrane
8. Pelta, made of microtubules and creates cell structure
9. Parabasal fibre
10. Axostyle, may be involved in movement or support for the cell
11. Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell
12. Vacuole
13. Hydrogenosome, produces molecular hydrogen and ATP (energy) in anaerobic conditions
14. Lysosome, holds enzymes

Classification

Before reclassification, the parabasalids were divided into about seven ^[9] to 10 orders depending on sources. Present classification divides Parabasalia into four orders, that is, Trichonymphida, Spirotrichonymphida, Cristamonadida, and Trichomonadida. ^[1]

• The trichomonads have one group of 4–6 flagella, one of which is attached to the side of the cell and often forms an undulating membrane. Many are found in vertebrate hosts, including Trichomonas vaginalis , which causes a sexually transmitted disease in humans.
• The other orders, formerly grouped as the hypermastigids, have a large number of flagellar clusters and are found exclusively in the guts of insects. (The term "Hypermastigida" is still occasionally encountered. ^[10] )

Evolution

The parabasalid Trichomonas vaginalis is not known to undergo meiosis. However, Malik et al. ^[11] examined T. vaginalis for the presence of 29 genes that function in meiosis and found 27 such genes, including eight genes specific to meiosis in model organisms. These findings suggested that the capability for meiosis, and hence sexual reproduction, was likely present in a recent parabasalid ancestor of T. vaginalis. ^[11]

References

1. Adl, Sina M.; Simpson, Alastair G. B.; Farmer, Mark A.; Andersen, Robert A.; Anderson, O. Roger; Barta, John R.; Bowser, Samuel S.; Brugerolle, Guy; Fensome, Robert A.; Fredericq, Suzanne; James, Timothy Y.; Karpov, Sergei; Kugrens, Paul; Krug, John; Lane, Christopher E.; Lewis, Louise A.; Lodge, Jean; Lynn, Denis H.; Mann, David G.; Mccourt, Richard M.; Mendoza, Leonel; Moestrup, Ojvind; Mozley-Standridge, Sharon E.; Nerad, Thomas A.; Shearer, Carol A.; Smirnov, Alexey V.; Spiegel, Frederick W.; Taylor, Max F. J. R. (October 2005). "The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists". The Journal of Eukaryotic Microbiology. 52 (5): 399–451. doi: 10.1111/j.1550-7408.2005.00053.x . PMID   16248873.
2. Ohkuma, Moriya; Iida, Toshiya; Ohtoko, Kuniyo; Yuzawa, Hiroe; Noda, Satoko; Viscogliosi, Eric; Kudo, Toshiaki (June 2005). "Molecular phylogeny of parabasalids inferred from small subunit rRNA sequences, with emphasis on the Hypermastigea". Molecular Phylogenetics and Evolution. 35 (3): 646–655. doi:10.1016/j.ympev.2005.02.013. PMID   15878133.
3. Simpson, A.G.B.; Čepička, I. (2009). "Amitochondriate Protists (Diplomonads, Parabasalids and Oxymonads)". Encyclopedia of Microbiology. Elsevier. doi:10.1016/B978-012373944-5.00246-7. ISBN   978-0-12-373944-5.
4. Frey, Caroline F.; Müller, Norbert (June 2012). "Tritrichomonas – Systematics of an enigmatic genus". Molecular and Cellular Probes. 26 (3): 132–136. doi:10.1016/j.mcp.2012.02.002.
5. Fiama das Neves Ortiz, Sharmila; Verdan, Raphael; Rocha, Gustavo Miranda; Miranda, Kildare; Benchimol, Marlene (June 2024). "The parabasal filaments of Trichomonas vaginalis: A new filament and observations using 0.8 nm-resolution scanning electron microscopy". Journal of Structural Biology: X. 9: 100099. doi:10.1016/j.yjsbx.2024.100099. PMC   10937234 . PMID   38487378.
6. Benchimol, Marlene; Ribeiro, Karla Consort; Mariante, Rafael Meyer; Alderete, John F. (2001). "Structure and division of the Golgi complex in Trichomonas vaginalis and Tritrichomonas foetus". European Journal of Cell Biology. 80 (9): 593–607. doi:10.1078/0171-9335-00191. PMID   11675935.
7. Bui, E T; Bradley, P J; Johnson, P J (3 September 1996). "A common evolutionary origin for mitochondria and hydrogenosomes". Proceedings of the National Academy of Sciences. 93 (18): 9651–9656. Bibcode:1996PNAS...93.9651B. doi: 10.1073/pnas.93.18.9651 . PMC   38483 . PMID   8790385.
8. Simpson, A.G.B.; Čepička, I. (2009). "Amitochondriate Protists (Diplomonads, Parabasalids and Oxymonads)". Encyclopedia of Microbiology. Elsevier. doi:10.1016/B978-012373944-5.00246-7. ISBN   978-0-12-373944-5.
9. Yubuki, Naoji; Céza, VÍT; Cepicka, Ivan; Yabuki, Akinori; Inagaki, Yuji; Nakayama, Takeshi; Inouye, Isao; Leander, Brian S (2010). "Cryptic Diversity of Free-Living Parabasalids, Pseudotrichomonas keilini and Lacusteria cypriaca n. G., n. Sp., as Inferred from Small Subunit rDNA Sequences". Journal of Eukaryotic Microbiology. 57 (6): 554–61. doi:10.1111/j.1550-7408.2010.00509.x. PMID   20880033. S2CID   4195962.
10. Carpenter, Kevin J.; Keeling, Patrick J. (July 2007). "Morphology and Phylogenetic Position of Eucomonympha imla (Parabasalia: Hypermastigida)". Journal of Eukaryotic Microbiology. 54 (4): 325–332. doi:10.1111/j.1550-7408.2007.00263.x. PMID   17669157.
11. Malik, Shehre-Banoo; Pightling, Arthur W.; Stefaniak, Lauren M.; Schurko, Andrew M.; Logsdon, John M. (6 August 2008). "An Expanded Inventory of Conserved Meiotic Genes Provides Evidence for Sex in Trichomonas vaginalis". PLOS ONE. 3 (8): e2879. Bibcode:2008PLoSO...3.2879M. doi: 10.1371/journal.pone.0002879 . PMC   2488364 . PMID   18663385.