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Chrompodellid

(Redirected from Apicomonada)

Chrompodellids are a clade of single-celled protists belonging to the Alveolata supergroup. It comprises two different polyphyletic groups of flagellates: the colpodellids, phagotrophic predators, and the chromerids, photosynthetic algae that live as symbionts of corals. These groups were independently discovered and described, but molecular phylogenetic analyses demonstrated that they are intermingled in a clade that is the closest relative to Apicomplexa, and they became collectively known as chrompodellids. Due to the history of their research, they are variously known in biological classification as Chromerida or Colpodellida (ICZN)/Colpodellales (ICN).

Chrompodellids
Typical life cycle stages of Vitrella brassicaformis, a chromerid (vc: vegetative cell, zs: zoosporangium, as: autosporangium)
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Alveolata
Phylum: Myzozoa
Class: Chromeridophyceae
Molinari & Guiry 2023[3]
Subclass: Chromeridophycidae
Mylnikov et al. 2000[4]
Order: Colpodellales
Cavalier-Smith 1993[1] emend. Adl et al. 2005, 2019[2][3]
Type genus
Colpodella
Cienkowsky 1865[1]
Families[2][3]
Synonyms
  • Apicomonadea Cavalier-Smith 1993 emend. 2017[5]
  • Chromerida Moore et al. 2008[6]
  • Chromeridophyta Guiry 2024[7]

Description and life cycle

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Chrompodellids are a clade of unicellular protists containing two functionally different groups: the photosynthetic "chromerids" and the predatory phagotrophic "colpodellids". Like other Alveolata, they present tubular mitochondrial cristae and highly flattened cortical alveoli[8] with microtubules underneath. They exhibit a conoid-like structure similar to that of apicomplexans, with an apical complex, a micropore and a rostrum. They live as flagellates with two anisokont (i.e. differently sized) flagella[1] that are heterodynamic (i.e. move in different patterns).[9] Some species exhibit thin mastigonemes in their anterior flagellum, while others bear bulbs.[9] Some species are capable of forming cysts.[2]

Colpodellids

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Colpodellids, represented by the genera Colpodella, Alphamonas, Voromonas and Chilovora, are free-living predatory phagotrophic flagellates.[9] They live as biflagellated single cells, 5–20 μm in length, with an open conoid and rhoptries used to hunt. They present genetic sequences of non-photosynthetic plastids, evidence of their phototroph ancestry.[8]

Some species, considered ectoparasites, do not ingest prey cells, but rather fully or partially "suck" their contents, a process known as myzocytosis, common among alveolates.[9][10] They feed on bacteria and other protozoa, such as bodonids, chrysomonads, bicosoecids, percolomonads and ciliates.[11] After feeding, they internalize their flagella, become cysts and divide into tetrads, similarly to the development of zoospores in Chromera. The cells conjugate after leaving the cyst, which could imply a sexual stage.[8]

Chromerids

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Chromerids, represented by the genera Chromera and Vitrella, are photosynthetic protists, and are thus considered algae. They exist in association with corals. For most of their life cycle, they live as round (coccoid) brownish immobile vegetative cells called autospores, surrounded by a thick resistant cell wall. They contain one chloroplast in each cell,[8] with chlorophyll a,[12] violaxanthin, and β-carotene.[8]

The two genera are markedly different from each other, both in phylogeny and life cycles. Chromera autospores are 5–7 μm in diameter. They asexually reproduce through binary division to develop autosporangia, which in turn harbor 2–4 autospores under an additional membrane. They also form zoosporangia, up to 15 μm in diameter, capable of generating 2–10 flagellated zoospores that strongly resemble colpodellids. This dispersal process is similar to the schizogony of apicomplexans. Sexual reproduction has not been observed. Under adverse environmental conditions, they form resistant cysts that remain viable for years. Similarly to apicomplexans, they undergo closed mitosis, without dissolving the nuclear envelope.[8] In addition, Chromera produces high amounts of an exclusive type of isofucoxanthin.[6]

Vitrella autospores, by contrast, start measuring 3 μm and grow up to 40 μm before transforming into sporangia that generate dozens of autospores or zoospores. There are two types of Vitrella zoospores: one is generated by budding from the mother cell and exhibits flagella outside the cytoplasm, the other develops axonemes and flagella within their cytoplasm and are ejected from the mother cell after maturing, though both types lack a pseudo-conoid. Some zoospores fuse, possibly representing a sexual stage in the life cycle.[8] In addition, Vitrella produces vaucheriaxanthin.[13]

Evolution

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Chrompodellids are the closest living relatives of the apicomplexan parasites, which evolved from a photosynthetic myzozoan ancestor, making chromerids the last remaining photosynthetic members of an otherwise parasitic clade within Alveolata.[14] The apicomplexans, chrompodellids, perkinsids and dinoflagellates constitute the clade Myzozoa, characterized by the apical complex and plastids derived from an event of secondary endosymbiosis with a red alga. The photosynthetic ability of these plastids was eventually lost in apicomplexans, colpodellids, perkinsids and other groups that transitioned into a predatory or parasitic lifestyle.[8] The following cladogram summarizes alveolate relationships and the internal relationships among most genera within the chrompodellid clade (chromerids marked with asterisks):[15][12][16]

Alveolata

Systematics

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Taxonomic history

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In 1993, protozoologist Thomas Cavalier-Smith described the order Colpodellida (under the ICZN, later regularized as Colpodellales in accordance to the ICN)[3] to contain what he considered one of the "most primitive flagellate apicomplexans", the genus Colpodella. This order was introduced in the class Apicomonadea along with the Perkinsida.[1] Cavalier-Smith treats this class as a member of the phylum Apicomplexa, while "true" apicomplexans are united under the name Sporozoa.[5] Although the inclusion of colpodellids within apicomplexans was not supported by other authors, phylogenetic studies demonstrated that they were sister clades.[17]

The first chromerid alga, Chromera velia, was discovered and isolated from Australian corals in 2001. It was described in 2008 as the first member of a new phylum Chromerida, followed by Vitrella brassicaformis in 2012.[13] They showed morphological resemblance to colpodellids and other myzozoans.[12] In the following years, phylogenetic studies reported the evolutionary proximity between colpodellids and chromerid algae.[6] This was supported by the discovery of retained vestigial plastids in some colpodellid species.[18] In 2015 there was strong support for a clade containing the two groups, phylogenetically mixed with each other, which rendered both as polyphyletic. The clade was given the provisional name "chrompodellids",[15] later referred to as Chrompodellida by posterior studies.[19]

Between 2004 and 2017, Cavalier-Smith retained the classification scheme of Apicomonadea, from which he excluded Perkinsida, leaving only colpodellids and chromerids across multiple orders. In addition, several genera of flagellates were added on the basis of morphological data: Algovora, Microvorax and Dinomonas.[20] Due to lacking molecular data, these genera have been excluded from later classifications.[2] Two genera, Chilovora and Alphamonas, were eventually rejected in his classification,[5] but later revisions by other authors maintain them as independent genera supported by molecular data.[2]

The treatment of chrompodellids as a subgroup of Apicomplexa, under the name of Apicomonadea, was rejected by the International Society of Protistologists. In a 2019 revision of eukaryotic classification, protistologists emended the previous name Colpodellida to contain all chrompodellids, and treated it as a direct subgroup of Alveolata, independent from Apicomplexa.[2] Later, phycologists advocated for this treatment as a separate phylum, and regularized it under the name of Chromerida or Chromeridophyta, composed of a single class Chromeridophyceae and a single order Colpodellales, in accordance to the nomenclatural rules of the ICN.[3][7] However, other authors consider them a subgroup of the phylum Myzozoa, together with apicomplexans, perkinsozoans and dinoflagellates.[15][5][8]

Classification

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As of 2023, chrompodellids are divided into four families and seven genera:[2][3]

References

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  1. ^ a b c d T Cavalier-Smith (December 1993). "Kingdom protozoa and its 18 phyla". Microbiological Reviews. 57 (4): 953–94. ISSN 0146-0749. PMC 372943. PMID 8302218. Wikidata Q24634634.
  2. ^ a b c d e f g h Sina M. Adl; David Bass; Christopher E. Lane; et al. (1 January 2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/JEU.12691. ISSN 1066-5234. PMC 6492006. PMID 30257078. Wikidata Q57086550.
  3. ^ a b c d e f Eduardo A. Molinari-Novoa; Michael D. Guiry (30 October 2023). "Nomenclatural notes on algae. VIII. Automatically typified names for some groups of alveolates" (PDF). Notulae Algarum. 2023 (304): 1–3.
  4. ^ A.P. Mylnikov; M.V. Krylov; A.O. Frolov (2000). "Таксономический ранг и место в системе протистов Colpodellida" Taksonomicheskiy rang i mesto v sisteme protistov Colpodellida [Taxonomic rank and place of Colpodellida in a system] (PDF). Parazitologiya (in Russian). 34 (1): 3–15.
  5. ^ a b c d Thomas Cavalier-Smith (5 September 2017). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/S00709-017-1147-3. ISSN 0033-183X. PMC 5756292. PMID 28875267. Wikidata Q47194626.
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  12. ^ a b c Jan Michálek (2020). Genomes of Chromerid Algae (PDF) (PhD thesis). Czech Republic: University of South Bohemia in České Budějovice.
  13. ^ a b c Oborník, M; Modrý, D; Lukeš, M; Cernotíková-Stříbrná, E; Cihlář, J; Tesařová, M; Kotabová, E; Vancová, M; Prášil, O; Lukeš, J (2012). "Morphology, Ultrastructure and Life Cycle of Vitrella brassicaformis n. sp., n. gen., a Novel Chromerid from the Great Barrier Reef". Protist. 163 (2): 306–323. doi:10.1016/j.protis.2011.09.001. PMID 22055836.
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  15. ^ a b c Jan Janouškovec; Denis Tikhonenkov; Fabien Burki; Alexis T Howe; Martin Kolísko; Alexander P Mylnikov; Patrick John Keeling (25 February 2015). "Factors mediating plastid dependency and the origins of parasitism in apicomplexans and their close relatives". Proceedings of the National Academy of Sciences of the United States of America. 112 (33): 10200–10207. Bibcode:2015PNAS..11210200J. doi:10.1073/PNAS.1423790112. ISSN 0027-8424. PMC 4547307. PMID 25717057. Wikidata Q30662251.
  16. ^ a b Varsha Mathur; Eric D. Salomaki; Kevin C. Wakeman; Ina Na; Waldan K. Kwong; Martin Kolísko; Patrick John Keeling (4 January 2023). "Reconstruction of Plastid Proteomes of Apicomplexans and Close Relatives Reveals the Major Evolutionary Outcomes of Cryptic Plastids". Molecular Biology and Evolution. 40 (1): msad002. doi:10.1093/MOLBEV/MSAD002. ISSN 0737-4038. PMC 9847631. PMID 36610734. Wikidata Q124684358.
  17. ^ Olga N Kuvardina; Brian S Leander; Vladimir V Aleshin; Alexander P Myl'nikov; Patrick John Keeling; Timur G Simdyanov (1 November 2002). "The phylogeny of colpodellids (Alveolata) using small subunit rRNA gene sequences suggests they are the free-living sister group to apicomplexans". Journal of Eukaryotic Microbiology. 49 (6): 498–504. doi:10.1111/J.1550-7408.2002.TB00235.X. ISSN 1066-5234. PMID 12503687. Wikidata Q34167276.
  18. ^ Gillian H Gile; Claudio H Slamovits (2014). "Transcriptomic analysis reveals evidence for a cryptic plastid in the colpodellid Voromonas pontica, a close relative of chromerids and apicomplexan parasites". PLOS One. 9 (5): e96258. Bibcode:2014PLoSO...996258G. doi:10.1371/JOURNAL.PONE.0096258. ISSN 1932-6203. PMC 4010437. PMID 24797661. Wikidata Q28657955.
  19. ^ Andrea Valigurová; Isabelle Florent (2 July 2021). "Nutrient Acquisition and Attachment Strategies in Basal Lineages: A Tough Nut to Crack in the Evolutionary Puzzle of Apicomplexa". Microorganisms. 9 (7): 1430. doi:10.3390/microorganisms9071430. PMC 8303630. PMID 34361866.
  20. ^ a b c T. Cavalier-Smith; E.E. Chao (September 2004). "Protalveolate phylogeny and systematics and the origins of Sporozoa and dinoflagellates (phylum Myzozoa nom. nov.)". European Journal of Protistology. 40 (3): 185–212. doi:10.1016/J.EJOP.2004.01.002. ISSN 0932-4739. Wikidata Q54540793.
  21. ^ Miroslav Oborník; Marie Vancová; De-Hua Lai; Jan Janouškovec; Patrick John Keeling; Julius Lukeš (1 January 2011). "Morphology and ultrastructure of multiple life cycle stages of the photosynthetic relative of apicomplexa, Chromera velia". Protist. 162 (1): 115–130. doi:10.1016/J.PROTIS.2010.02.004. ISSN 1434-4610. PMID 20643580. Wikidata Q34126892.
  22. ^ L. Cienkowski (1865). "Beiträge zur Kenntniss der Monaden" (PDF). Archiv für Mikroskopische Anatomie. 1 (1): 203–232. doi:10.1007/BF02961414. S2CID 84323025.
  23. ^ Ruth Patten (October 1936). "Notes on a New Protozoon, Piridium sociabile n.gen., n.sp., from the Foot of Buccinum undatum". Parasitology. 28 (04): 502. doi:10.1017/S003118200002268X. ISSN 0031-1820. Wikidata Q54495349.
  24. ^ Jan Janouškovec; Gita Paskerova; Tatiana S Miroliubova; Kirill V Mikhailov; Thomas Birley; Vladimir V. Aleoshin; Timur Simdyanov (16 August 2019). "Apicomplexan-like parasites are polyphyletic and widely but selectively dependent on cryptic plastid organelles". eLife. 8. doi:10.7554/ELIFE.49662. ISSN 2050-084X. PMC 6733595. PMID 31418692. Wikidata Q83229299.
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