parabasalid
{{short description|Group of flagellated protists}}
{{Automatic taxobox
| image = Trichomonas Giemsa DPDx.JPG
| image_alt = Two trophozoites of "Trichomonas vaginalis" stained with Giemsa
| image_caption = Two trophozoites of Trichomonas vaginalis stained with Giemsa
| taxon = Parabasalia
| authority = Honigberg 1973
| synonyms =
| synonyms_ref =
| subdivision_ranks = Orders
| subdivision =
}}
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{{cite journal |last1=Ohkuma |first1=Moriya |last2=Iida |first2=Toshiya |last3=Ohtoko |first3=Kuniyo |last4=Yuzawa |first4=Hiroe |last5=Noda |first5=Satoko |last6=Viscogliosi |first6=Eric |last7=Kudo |first7=Toshiaki |title=Molecular phylogeny of parabasalids inferred from small subunit rRNA sequences, with emphasis on the Hypermastigea |journal=Molecular Phylogenetics and Evolution |date=June 2005 |volume=35 |issue=3 |pages=646–655 |doi=10.1016/j.ympev.2005.02.013 |pmid=15878133 }} 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.{{cite book |doi=10.1016/B978-012373944-5.00246-7 |date=2009 |isbn=978-0-12-373944-5 |last1=Simpson |first1=A.G.B. |last2=Čepička |first2=I. |title=Encyclopedia of Microbiology |chapter=Amitochondriate Protists (Diplomonads, Parabasalids and Oxymonads) |publisher=Elsevier }}{{cite journal |last1=Frey |first1=Caroline F. |last2=Müller |first2=Norbert |title=Tritrichomonas – Systematics of an enigmatic genus |journal=Molecular and Cellular Probes |date=June 2012 |volume=26 |issue=3 |pages=132–136 |doi=10.1016/j.mcp.2012.02.002 }}
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.{{cite journal |last1=Fiama das Neves Ortiz |first1=Sharmila |last2=Verdan |first2=Raphael |last3=Rocha |first3=Gustavo Miranda |last4=Miranda |first4=Kildare |last5=Benchimol |first5=Marlene |title=The parabasal filaments of Trichomonas vaginalis: A new filament and observations using 0.8 nm-resolution scanning electron microscopy |journal=Journal of Structural Biology: X |date=June 2024 |volume=9 |pages=100099 |doi=10.1016/j.yjsbx.2024.100099 |pmid=38487378 |pmc=10937234 }} Attachment of a parabasal fiber to the first Golgi cisterna by thin filaments has been reported in Tritrichomonas foetus.{{cite journal|title=Structure and division of the Golgi complex in Trichomonas vaginalis and Tritrichomonas foetus|journal=European Journal of Cell Biology|volume=80|pages=593–607|year=2001|doi=10.1078/0171-9335-00191|last1=Benchimol|first1=Marlene|last2=Ribeiro|first2=Karla Consort|last3=Mariante|first3=Rafael Meyer|last4=Alderete|first4=John F.|issue=9 |pmid=11675935}} 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|date=January 2025}}
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.{{cite journal |last1=Bui |first1=E T |last2=Bradley |first2=P J |last3=Johnson |first3=P J |title=A common evolutionary origin for mitochondria and hydrogenosomes |journal=Proceedings of the National Academy of Sciences |date=3 September 1996 |volume=93 |issue=18 |pages=9651–9656 |doi=10.1073/pnas.93.18.9651 |pmid=8790385 |pmc=38483 |bibcode=1996PNAS...93.9651B |doi-access=free }} 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|date=February 2025}}
Recurrent flagellum|
Undulating membrane|
Golgi apparatus; modifies proteins and sends them out of the cell|
Costa, a striated fiber associated with the undulating membrane{{cite book |doi=10.1016/B978-012373944-5.00246-7 |date=2009 |isbn=978-0-12-373944-5 |last1=Simpson |first1=A.G.B. |last2=Čepička |first2=I. |title=Encyclopedia of Microbiology |chapter=Amitochondriate Protists (Diplomonads, Parabasalids and Oxymonads) |publisher=Elsevier }}
|
Pelta, made of microtubules and creates cell structure|
Parabasal fibre|
Axostyle, may be involved in movement or support for the cell|
Endoplasmic reticulum, the transport network for molecules going to specific parts of the cell|
Hydrogenosome, produces molecular hydrogen and ATP (energy) in anaerobic conditions|
Lysosome, holds enzymes|}}]]
Classification
Before reclassification, the parabasalids were divided into about seven{{cite journal|doi=10.1111/j.1550-7408.2010.00509.x|pmid=20880033|title=Cryptic Diversity of Free-Living Parabasalids, Pseudotrichomonas keilini and Lacusteria cypriaca n. G., n. Sp., as Inferred from Small Subunit rDNA Sequences|journal=Journal of Eukaryotic Microbiology|volume=57|issue=6|pages=554–61|year=2010|last1=Yubuki|first1=Naoji|last2=Céza|first2=VÍT|last3=Cepicka|first3=Ivan|last4=Yabuki|first4=Akinori|last5=Inagaki|first5=Yuji|last6=Nakayama|first6=Takeshi|last7=Inouye|first7=Isao|last8=Leander|first8=Brian S|s2cid=4195962}} to 10 orders depending on sources. Present classification divides Parabasalia into four orders, that is, Trichonymphida, Spirotrichonymphida, Cristamonadida, and Trichomonadida.
- 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.{{cite journal |last1=Carpenter |first1=Kevin J. |last2=Keeling |first2=Patrick J. |title=Morphology and Phylogenetic Position of Eucomonympha imla (Parabasalia: Hypermastigida) |journal=Journal of Eukaryotic Microbiology |date=July 2007 |volume=54 |issue=4 |pages=325–332 |doi=10.1111/j.1550-7408.2007.00263.x |pmid=17669157 }})
Evolution
The parabasalid Trichomonas vaginalis is not known to undergo meiosis. However, Malik et al.{{cite journal |last1=Malik |first1=Shehre-Banoo |last2=Pightling |first2=Arthur W. |last3=Stefaniak |first3=Lauren M. |last4=Schurko |first4=Andrew M. |last5=Logsdon |first5=John M. |title=An Expanded Inventory of Conserved Meiotic Genes Provides Evidence for Sex in Trichomonas vaginalis |journal=PLOS ONE |date=6 August 2008 |volume=3 |issue=8 |pages=e2879 |doi=10.1371/journal.pone.0002879 |pmid=18663385 |pmc=2488364 |bibcode=2008PLoSO...3.2879M |doi-access=free }} 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.
References
{{Reflist}}
{{Eukaryota}}
{{Metamonada}}
{{Taxonbar|from=Q134585}}