Colponemid

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Colponemids
Colponema vietnamica 4A pone.0095467.tif
SEM image of Colponema vietnamica showing anterior (af) and posterior (pf) flagella, and an acroneme (an).
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Alveolata
Order: Colponemida
Cavalier-Smith 1993 emend. Adl et al. 2019 [1]
Groups included
Cladistically included but traditionally excluded taxa
Synonyms
  • Protalveolata Cavalier-Smith 1991 em. 2017 [2]

Colponemids are free-living alveolates, unicellular flagellates related to dinoflagellates, apicomplexans and ciliates. They are predators of other small eukaryotes, found in freshwater, marine and soil environments. They do not form a solid clade, but a sparse group of deep-branching alveolate lineages.

Contents

Biology

Colponemids are flagellated unicellular protists, 8 to 30 μm long, with rounded cell bodies that bear two heterodynamic flagella for rapid swimming. They are only present as swimming cells during their life cycle. Reproduction or resting cysts are unknown. [3]

Cell structure

As other alveolates, all colponemids exhibit cortical alveoli and tubular mitochondrial cristae. They present a three-membrane alveolar pellicle without fibrils, theca or micropores. Within the cell is a vesicular nucleus with a central nucleolus, as well as a very large digestive vacuole (or food vacuole) located at the posterior end of the cell, and a contractile vacuole at the anterior end. In addition, the cytoplasm contains flask-shaped extrusomes. [3] The anterior flagellum has thin non-hollow mastigonemes at its base (or proximal end), unlike the hollow tripartite mastigonemes found in stramenopiles. The posterior flagellum has a fold [3] or 'vane'. [4]

As many basal eukaryotes, they present a ventral groove for feeding, tiny in Loeffela , substantial in Palustrimonas [4] and absent in Acavomonas . [3] Supporting this longitudinal groove are two microtubule bands. [3]

Feeding

All colponemids share a raptorial predatory lifestyle, where they move actively to encounter and capture their prey. Prey cells are ingested through the anterior region of the ventral groove, on the right side of the cell (i.e. to the right of the posterior flagellum). During the early stages of phagocytosis, flask-shaped extrusomes within the colponemid cell seem to play a role in subduing the much larger prey cells. [4]

Ecology

Colponemids are found in freshwater, marine and soil environments. [1] They are obligate eukaryovores or eukaryotrophs, free-living predators that feed on other microscopic eukaryotes by capturing and ingesting entire cells. [3]

Evolution

Colponemid phylogeny

Myzozoa (apicomplexans & dinoflagellates)

Neocolponema

Palustrimonas

Ciliophora (ciliates)

Acavomonas

Colponema

Loeffela

Cladogram of Alveolata showing the position of colponemid genera (in bold). Based on a 2023 phylogenetic analysis using SSU rDNA sequences. [4]

Colponemids are not a clade, i.e. do not form an independent evolutionary lineage within eukaryotes. Instead, they are a series of deep-branching lineages spread within the larger Alveolata group. Phylogenetic analyses recover some colponemids at the base of Myzozoa (the clade uniting apicomplexans and dinoflagellates), such as Acavomonas , while others appear at the base of all alveolates. [4]

The method of feeding in colponemids perhaps represents the ancestral alveolate state, preceding myzocytosis in their myzozoan relatives. In addition, they possibly constitute the evolutionary link to more basal protists with ventral grooves used in feeding, i.e. 'excavates' (such as metamonads, jakobids and malawimonads). These basal organisms feed on suspended particles driving them into their ventral groove by the beating of their posterior flagellum, an arrangement comparable to that seen among colponemids during feeding. However, there are large differences between their feeding processes. Namely, colponemids are not suspension feeders, and phagocytosis occurs in their anterior end, not the posterior end as in excavates. [4]

Classification

Due to the non-monophyletic nature of this group of protists, a new method of classification was proposed in 2014 which divided the Alveolata clade in four phyla: Myzozoa, Acavomonidia (with the newly described genus Acavomonas ), Colponemidia (with the genus Colponema ) and Ciliophora. This change was proposed to strive away from the paraphyletic taxon "Colponemida" and instead group each colponemid lineage in its own separate phylum. [3] In 2023, three more genera were added to Colponemida: newly described Loeffela and Neocolponema , together with the previously unsequenced genus Palustrimonas , without their inclusion in new phyla. [4] Currently, five genera of colponemids are recognised: [4]

Related Research Articles

<span class="mw-page-title-main">Stramenopile</span> Clade of eukaryotes

The Stramenopiles, also called Heterokonts, are a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have been secondarily lost. Stramenopiles represent one of the three major clades in the SAR supergroup, along with Alveolata and Rhizaria.

<span class="mw-page-title-main">Alveolate</span> Superphylum of protists

The alveolates are a group of protists, considered a major clade and superphylum within Eukarya. They are currently grouped with the stramenopiles and Rhizaria among the protists with tubulocristate mitochondria into the SAR supergroup.

<span class="mw-page-title-main">Cryptomonad</span> Group of algae and colorless flagellates

The cryptomonads are a group of algae, most of which have plastids. They are traditionally considered a division of algae among phycologists, under the name of Cryptophyta. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella. Some may exhibit mixotrophy. They are classified as clade Cryptomonada, which is divided into two classes: heterotrophic Goniomonadea and phototrophic Cryptophyceae. The two groups are united under three shared morphological characteristics: presence of a periplast, ejectisomes with secondary scroll, and mitochondrial cristae with flat tubules. Genetic studies as early as 1994 also supported the hypothesis that Goniomonas was sister to Cryptophyceae. A study in 2018 found strong evidence that the common ancestor of Cryptomonada was an autotrophic protist.

<span class="mw-page-title-main">Chromista</span> Eukaryotic biological kingdom

Chromista is a proposed but polyphyletic biological kingdom, refined from the Chromalveolata, consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles (plastids). It includes all eukaryotes whose plastids contain chlorophyll c and are surrounded by four membranes. If the ancestor already possessed chloroplasts derived by endosymbiosis from red algae, all non-photosynthetic Chromista have secondarily lost the ability to photosynthesise. Its members might have arisen independently as separate evolutionary groups from the last eukaryotic common ancestor.

<span class="mw-page-title-main">Telonemia</span> Phylum of single-celled organisms

Telonemia is a phylum of microscopic eukaryotes commonly known as telonemids. They are unicellular free-living flagellates with a unique combination of cell structures, including a highly complex cytoskeleton unseen in other eukaryotes.

Carpediemonas is genus of Metamonada, and belongs to the group Excavata. This organism is a unicellular flagellated eukaryote that was first discovered in substrate samples from the Great Barrier Reef. Carpediemonas can be found in anaerobic intertidal sediment, where it feeds on bacteria. A feature of this species is the presence of a feeding groove, a characteristic of the excavates. Like most other metamonads, Carpediemonas does not rely on an aerobic mitochondrion to produce energy. Instead, it contains hydrogenosomes that are used to produce ATP. This organism has two flagella: a posterior one used for feeding on the substrate, and an anterior one that moves in a slower sweeping motion. Carpediemonas is assigned to the fornicates, where similar Carpediemonas-like organisms are used in researching the evolution within excavates. Although Carpediemonas is a member of the metamonads, it is unusual in the sense that it is free-living and has three basal bodies.

<i>Malawimonas</i> Genus of micro-organisms

Malawimonas is genus of unicellular, heterotrophic flagellates with uncertain phylogenetic affinities. They have variably being assigned to Excavata and Loukozoa. Recent studies suggest they may be closely related to the Podiata.

<span class="mw-page-title-main">Bigyra</span> Phylum of single-celled organisms

Bigyra is a phylum of microscopic eukaryotes that are found at the base of the Stramenopiles clade. It includes three well-known heterotrophic groups Bicosoecida, Opalinata and Labyrinthulomycetes, as well as several small clades initially discovered through environmental DNA samples: Nanomonadea, Placididea, Opalomonadea and Eogyrea. The classification of Bigyra has changed several times since its origin, and its monophyly remains unresolved.

<i>Colpodella</i> Genus of single-celled organisms

Colpodella is a genus of alveolates comprising 5 species, and two further possible species: They share all the synapomorphies of apicomplexans, but are free-living, rather than parasitic. Many members of this genus were previously assigned to a different genus - Spiromonas.

<span class="mw-page-title-main">Myzozoa</span> Group of single-celled organisms

Myzozoa is a grouping of specific phyla within Alveolata, that either feed through myzocytosis, or were ancestrally capable of feeding through myzocytosis.

<span class="mw-page-title-main">Katablepharid</span> Group of algae

The kathablepharids or katablepharids are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus Kathablepharis. This genus is corrected to Katablepharis under botanical nomenclature, but the original spelling is maintained under zoological nomenclature. They are single-celled protists with two anteriorly directed flagella, an anterior cytostome for ingesting eukaryotic prey, and a sheath that covers the cell membrane. They have extrusomes known as ejectisomes, as well as tubular mitochondrial cristae.

<span class="mw-page-title-main">Perkinsea</span> Group of intracellular parasites

Perkinsids are single-celled protists that live as intracellular parasites of a variety of other organisms. They are classified as the class Perkinsea within the monotypic phylum Perkinsozoa. It is part of the eukaryotic supergroup Alveolata, along with dinoflagellates, their closest relatives, and another parasitic group known as Apicomplexa. Perkinsids are found in aquatic environments, as parasites of dinoflagellates and various animals.

<i>Parvilucifera</i> Genus of single-celled organisms

Parvilucifera is a genus of marine alveolates that behave as endoparasites of dinoflagellates. It was described in 1999 by biologists Fredrik Norén and Øjvind Moestrup, who identified the genus among collections of Dinophysis dinoflagellates off the coast of Sweden. Initially mistaken for products of sexual reproduction, the round bodies found within these collections were eventually recognized as sporangia, spherical structures that generate zoospores of a parasitic protist. This organism was later identified as P. infectans, the type species. The examination of this organism and its close genetic relationship to Perkinsus led to the creation of the Perkinsozoa phylum within the Alveolata group.

Platysulcus tardus is an eukaryotic microorganism that was recently discovered to be the earliest diverging lineage of the Heterokont phylogenetic tree. It is the only member of the family Platysulcidae, order Platysulcida and class Platysulcea.

Rhodelphis is a single-celled archaeplastid that lives in aquatic environments and is the sister group to red algae and possibly Picozoa. While red algae have no flagellated stages and are generally photoautotrophic, Rhodelphis is a flagellated predator containing a non-photosynthetic plastid. This group is important to the understanding of plastid evolution because they provide insight into the morphology and biochemistry of early archaeplastids. Rhodelphis contains a remnant plastid that is not capable of photosynthesis, but may play a role in biochemical pathways in the cell like heme synthesis and iron-sulfur clustering. The plastid does not have a genome, but genes are targeted to it from the nucleus. Rhodelphis is ovoid with a tapered anterior end bearing two perpendicularly-oriented flagella.

Colponema is a genus of single-celled flagellates that feed on eukaryotes in aquatic environments and soil. The genus contains 6 known species and has not been thoroughly studied. Colponema has two flagella which originate just below the anterior end of the cell. One extends forwards and the other runs through a deep groove in the surface and extends backwards. Colponema is a predator that feeds on smaller flagellates using its ventral groove. Like many other alveolates, they possess trichocysts, tubular mitochondrial cristae, and alveoli. It has been recently proposed that Colponema may be the sister group to all other alveolates. The genus could help us understand the origin of alveolates and shed light on features that are ancestral to all eukaryotes.

<span class="mw-page-title-main">Cortical alveolum</span> Cellular organelle found in protists

The cortical alveolum is a cellular organelle consisting of a vesicle located under the cytoplasmic membrane, to which they give support. The term "corticate" comes from an evolutionary hypothesis about the common origin of kingdoms Plantae and Chromista, because both kingdoms have cortical alveoli in at least one phylum. At least three protist lineages exhibit these structures: Telonemia, Alveolata and Glaucophyta.

<i>Orciraptor</i> Genus of predatorial protists

Orciraptor is a genus of heterotrophic protists, containing the single species Orciraptor agilis. It belongs to the family Viridiraptoridae, in the phylum Cercozoa.

<i>Syssomonas</i> Genus of protists

Syssomonas is a monotypic genus of unicellular flagellated protists containing the species Syssomonas multiformis. It is a member of Pluriformea inside the lineage of Holozoa, a clade containing animals and their closest protistan relatives. It lives in freshwater habitats. It has a complex life cycle that includes unicellular amoeboid and flagellated phases, as well as multicellular aggregates, depending on the growth medium and nutritional state.

<span class="mw-page-title-main">Chrompodellid</span> Clade of alveolates

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).

References

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