Karyorelictea

Last updated

Karyorelictea
Loxodes rostrum from page 267 of "American journal of physiology" (1898).jpg
Illustration of Loxodes rostrum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Alveolata
Phylum: Ciliophora
Subphylum: Postciliodesmatophora
Class: Karyorelictea
Corliss, 1974  [1]
Orders [2]

Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, Loxodes , is found in freshwater.

Contents

The majority of karyorelict taxa have not been cultivated in the laboratory, although clonal lines of Loxodes have been developed.

Systematics

According to Lynn (2008), the Karyorelictea class is divided into three orders: [2]

These three orders were defined morphologically, and have been confirmed with molecular phylogenetics. [3]

An additional family, Wilbertomorphidae, is of uncertain affiliation and has not been assigned to an order. [4]

Nuclear dimorphism

All ciliates, including karyorelicteans, possess two different kinds of nucleus, which separate the functions of gene expression and sexual recombination. The macronuclei, or somatic nuclei, are the site of transcription, while the smaller micronuclei, or germline nuclei, are only active during sexual reproduction, where they first undergo meiosis to form gametic nuclei, which are exchanged when two mating cells conjugate. Two gametic nuclei fuse to form a zygotic nucleus, which divides by mitosis into two daughter nuclei, one of which develops into a new micronucleus and the other into a macronucleus; the old macronucleus typically disintegrates (see main article).

In most ciliates, a macronucleus can divide during asexual reproduction to form new daughter macronuclei, through a process called amitosis. However, in karyorelicteans, the macronuclei are unable to divide. Instead, they must be produced by division and differentiation of a micronucleus every time, even during asexual reproduction. [5] [6]

Because of their non-dividing somatic macronuclei, the karyorelicteans were thought to represent an intermediate evolutionary stage between the hypothetical ancestor of ciliates that did not have nuclear dualism, and the other more "advanced" ciliates which had both nuclear dualism and macronuclei that could divide by amitosis. The name of the group therefore makes reference to their supposedly "primitive" nuclei. [7] This theory has since been superseded, as molecular phylogenies have shown that the karyorelicteans are not the most "primitive" or basally-branching group of ciliates. [8]

Ecology

Almost all karyorelictean species, except Loxodes, have been described from the marine interstitial habitat, where they live in the pore-water spaces between sediment grains. [9] Animals from such habitats are known as meiofauna, and karyorelicteans have many morphological similarities to meiofaunal animals despite being protists: most karyorelicteans are relatively large (1 mm or more in length), have a worm-like (vermiform) body shape with an elongated tail, and exhibit thigmotactic behavior. [10] Most karyorelicteans feed on bacteria or algae, and prefer microaerobic conditions. [11] [12] [13] However, one genus, Kentrophoros , lacks an oral apparatus and feeds instead on symbiotic sulfur-oxidizing bacteria that are attached to one side of the cell. [14] [15]

Etymology

The class name Karyorelictea derives from the ancient greek κάρυον (káruon), meaning "hard-shelled seed, or nucleus", [16] [17] and from the Latin relictus , meaning 'abandoned'. [18]

Alternative genetic code

An alternative genetic code is used by the nuclear genome of some karyorelictid ciliates (e.g. Parduczia sp.). [19] This code corresponds to translation table 27 and involves the reassignment of three codons:

Related Research Articles

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

The heterotrichs are a class of ciliates. They typically have a prominent adoral zone of membranelles circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are typically compressed or conical in form. These include some of the largest protozoa, such as Stentor and Spirostomum, as well as many brightly pigmented forms, such as certain Blepharisma.

<i>Paramecium</i> Genus of unicellular ciliates, commonly studied as a representative of the ciliate group

Paramecium is a genus of eukaryotic, unicellular ciliates, commonly studied as a model organism of the ciliate group. Paramecium are widespread in freshwater, brackish, and marine environments and are often abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, they have been widely used in classrooms and laboratories to study biological processes. The usefulness of Paramecium as a model organism has caused one ciliate researcher to characterize it as the "white rat" of the phylum Ciliophora.

<i>Stephanopogon</i> Genus of flagellate marine protozoan

Stephanopogon is a genus of flagellated marine protist that superficially resembles a ciliate.

<span class="mw-page-title-main">Nuclear dimorphism</span>

Nuclear dimorphism is a term referred to the special characteristic of having two different kinds of nuclei in a cell. There are many differences between the types of nuclei. This feature is observed in protozoan ciliates, like Tetrahymena, and some foraminifera. Ciliates contain two nucleus types: a macronucleus that is primarily used to control metabolism, and a micronucleus which performs reproductive functions and generates the macronucleus. The compositions of the nuclear pore complexes help determine the properties of the macronucleus and micronucleus. Nuclear dimorphism is subject to complex epigenetic controls. Nuclear dimorphism is continuously being studied to understand exactly how the mechanism works and how it is beneficial to cells. Learning about nuclear dimorphism is beneficial to understanding old eukaryotic mechanisms that have been preserved within these unicellular organisms but did not evolve into multicellular eukaryotes.

Epigenetic controls in ciliates is about the unique characteristic of Ciliates, which is that they possess two kinds of nuclei : a micronucleus used for inheritance, and a macronucleus, which controls the metabolism. The micronucleus contains the entirety of the genome whereas the macronucleus only contains the DNA necessary for vegetative growth. The macronucleus divides via amitosis, whereas the micronucleus undergoes typical mitosis. During sexual development a new macronucleus is formed from the meiosis of the micronucleus, where the removal of transposons occurs. On the division or reproduction of ciliates, the two nuclei are under several epigenetic controls.

<i>Spirostomum</i>

Spirostomum is a genus of ciliated protists in the class Heterotrichea. It is known for being very contractile. Having been first identified by Christian Gottfried Ehrenberg in 1834, further research has identified eight additional true morphospecies. This bacterivore genus mainly lives in the sediment deposits at the bottom of various aquatic habitats, and members possess rquA genes that could be responsible for their ability to survive in these hypoxic and anoxic environments. They are identifiable by their relatively large tubular/flat vermiform bodies. Their life cycle consists of a growth stage, in which they mature, and asexual and sexual reproduction stages. Some species are model organisms for studies on human pathogenic bacteria, while others are sensitive and accurate bioindicators for toxic substances.

<i>Paramecium caudatum</i> Species of single-celled organism

Paramecium caudatum is a species of unicellular protist in the phylum Ciliophora. They can reach 0.33 mm in length and are covered with minute hair-like organelles called cilia. The cilia are used in locomotion and feeding. The species is very common, and widespread in marine, brackish and freshwater environments.

Loxodes is a genus of karyorelictean ciliates, belonging to family Loxodidae. It is the only known karyorelictean ciliate that lives in freshwater habitats.

<span class="mw-page-title-main">Ciliate</span> Taxon of protozoans with hair-like organelles called cilia

The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation.

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

Euplotes is a genus of ciliates in the subclass Euplotia. Species are widely distributed in marine and freshwater environments, as well as soil and moss. Most members of the genus are free-living, but two species have been recorded as commensal organisms in the digestive tracts of sea urchins.

<i>Chilodonella uncinata</i> Species of single-celled organism

Chilodonella uncinata is a single-celled organism of the ciliate class of alveoles. As a ciliate, C. uncinata has cilia covering its body and a dual nuclear structure, the micronucleus and macronucleus. Unlike some other ciliates, C. uncinata contains millions of minichromosomes in its macronucleus while its micronucleus is estimated to contain 3 chromosomes. Childonella uncinata is the causative agent of Chilodonelloza, a disease that affects the gills and skin of fresh water fish, and may act as a facultative of mosquito larva.

<i>Colpidium colpoda</i> Species of protozoan

Colpidium colpoda are free-living ciliates commonly found in many freshwater environments including streams, rivers, lakes and ponds across the world. Colpidium colpoda is also frequently found inhabiting wastewater treatment plants. This species is used as an indicator of water quality and waste treatment plant performance.

<span class="mw-page-title-main">Loxodidae</span> Family of protists

Loxodidae is a family of karyorelict ciliates.

Remanella is a genus of karyorelict ciliates, belonging to family Loxodidae. Whereas Remanella inhabits brackish and marine waters, Loxodes – the other loxodid genus – is a freshwater taxon.

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

Intramacronucleata is a subphylum of ciliates. The group is characterized by the manner in which division of the macronucleus is accomplished during binary fission of the cell. In ciliates of this subphylum, division of the macronucleus is achieved by the action of microtubules which are assembled inside the macronucleus itself. This is in contrast to heterotrich ciliates of the subphylum Postciliodesmatophora, in which division of the macronucleus relies on microtubules formed outside the macronuclear envelope.

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

Armophorea is a class of ciliates in the subphylum Intramacronucleata. . It was first resolved in 2004 and comprises three orders: Metopida, Clevelandellida, and Armophorida. Previously members of this class were thought to be heterotrichs because of similarities in morphology, most notably a characteristic dense arrangement of cilia surrounding their oral structures. However, the development of genetic tools and subsequent incorporation of DNA sequence information has led to major revisions in the evolutionary relationships of many protists, including ciliates. Metopids, clevelandellids, and armophorids were grouped into this class based on similarities in their small subunit rRNA sequences, making them one of two so-called "riboclasses" of ciliates, however, recent analyses suggest that Armophorida may not be related to the other two orders.

The genome of most cells of eukaryotes remains mainly constant during life. However, there are cases of genome being altered in specific cells or in different life cycle stages during development. For example, not every human cell has the same genetic content as red blood cells which are devoid of nucleus. One of the best known groups in respect of changes in somatic genome are ciliates. The process resulting in a variation of somatic genome that differs from germline genome is called somatic genome processing.

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

Kentrophoros is a genus of ciliates in the class Karyorelictea. Ciliates in this genus lack a distinct oral apparatus and depend primarily on symbiotic bacteria for their nutrition.

Wilbertomorphidae is a family of karyorelictean ciliates. The family is monotypic, because it contains a single genus Wilbertomorpha with a single known species, Wilbertomorpha colpoda.

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

Trachelocercidae is a family of ciliates in the class Karyorelictea.

References

  1. ↑ WoRMS (2009). "Karyorelictea". World Ciliophora Database. World Register of Marine Species . Retrieved July 21, 2010.
  2. 1 2 Lynn, Denis (2008). The Ciliated Protozoa: Characterization, Classification, and Guide to the Literature. Springer. ISBN   978-1-4020-8239-9.
  3. ↑ Ilaria Andreoli; Lara Mangini; Filippo Ferrantini; Giovanni Santangelo; Franco Verni; Giulio Petroni (16 October 2009). "Molecular phylogeny of unculturable Karyorelictea (Alveolata, Ciliophora)". Zoologica Scripta . 38 (6): 651–662. doi:10.1111/J.1463-6409.2009.00395.X. ISSN   0300-3256. S2CID   84951188. Wikidata   Q124486881.
  4. ↑ Yuan Xu; Jiamei Li; Weibo Song; Alan Warren (6 July 2013). "Phylogeny and establishment of a new ciliate family, Wilbertomorphidae fam. nov. (Ciliophora, Karyorelictea), a highly specialized taxon represented by Wilbertomorpha colpoda gen. nov., spec. nov". Journal of Eukaryotic Microbiology . 60 (5): 480–489. doi:10.1111/JEU.12055. ISSN   1066-5234. PMID   23829190. Wikidata   Q30653609.
  5. ↑ Ying Yan; Anna J Rogers; Feng Gao; Laura A. Katz (22 May 2017). "Unusual features of non-dividing somatic macronuclei in the ciliate class Karyorelictea". European Journal of Protistology . 61 (Pt B): 399–408. doi:10.1016/J.EJOP.2017.05.002. ISSN   0932-4739. PMC   5831164 . PMID   28673471. Wikidata   Q34558450.
  6. ↑ I B Raikov (1 January 1985). "Primitive never-dividing macronuclei of some lower ciliates". International Review of Cytology. 95: 267–325. doi:10.1016/S0074-7696(08)60584-7. ISSN   0074-7696. PMID   2414246. Wikidata   Q38154201.
  7. ↑ Corliss, J. O.; Hartwig, E. (1977). "The "primitive" interstitial ciliates: their ecology, nuclear uniquenesses, and postulated place in the evolution and systematics of the phylum Ciliophora". Mikrofauna Meeresbodens. 61: 65–88.
  8. ↑ Feng Gao; Alan Warren; Qianqian Zhang; et al. (29 April 2016). "The All-Data-Based Evolutionary Hypothesis of Ciliated Protists with a Revised Classification of the Phylum Ciliophora (Eukaryota, Alveolata)". Scientific Reports . 6: 24874. doi:10.1038/SREP24874. ISSN   2045-2322. PMC   4850378 . PMID   27126745. Wikidata   Q28833826.
  9. ↑ Foissner, Wilhelm (1998). "The karyorelictids (Protozoa: Ciliophora), a unique and enigmatic assemblage of marine, interstitial ciliates: a review emphasizing ciliary patterns and evolution". In Coombs, G.H.; Vickerman, K.; Sleigh, M.A.; Warren, A. (eds.). Evolutionary relationships among Protozoa. Springer. pp. 305–325. ISBN   978-0-412-79800-9.
  10. ↑ Giere, Olav (2009). Meiobenthology : the microscopic motile fauna of aquatic sediments (2nd ed.). Springer. ISBN   978-3-540-68661-3. OCLC   310352202.
  11. ↑ Tom Fenchel (31 July 1969). "The ecology of marine microbenthos IV. Structure and function of the benthic ecosystem, its chemical and physical factors and the microfauna commuities with special reference to the ciliated protozoa". Ophelia. 6 (1): 1–182. doi:10.1080/00785326.1969.10409647. ISSN   0078-5326. Wikidata   Q114642373.
  12. ↑ Tom Fenchel; Bland Finlay (24 September 2008). "Oxygen and the spatial structure of microbial communities". Biological Reviews. 83 (4): 553–569. doi:10.1111/J.1469-185X.2008.00054.X. ISSN   1464-7931. PMID   18823390. S2CID   21908644. Wikidata   Q37281625.
  13. ↑ Fauré-Fremiet, E (1950). "Écologie des ciliés psammophiles littoraux". Bull Biol Fr Belg. 84 (1): 35–75. PMID   15420543.
  14. ↑ Finlay, Bland; Fenchel, Tom (1 July 1989). "Everlasting picnic for protozoa". New Scientist: 66–69.
  15. ↑ Fenchel, Tom; Finlay, Bland (1989). "Kentrophoros: A mouthless ciliate with a symbiotic kitchen garden". Ophelia. 30: 75–93.
  16. ↑ Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN   978-2010035289. OCLC   461974285.
  17. ↑ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved 2017-01-24.
  18. ↑ Gaffiot, Félix (1934). Dictionnaire illustré Latin-Français (in French). Paris: Librairie Hachette. p. 1278. Retrieved 14 October 2017.
  19. ↑ Estienne Carl Swart; Valentina Serra; Giulio Petroni; Mariusz Nowacki (14 July 2016). "Genetic Codes with No Dedicated Stop Codon: Context-Dependent Translation Termination". Cell . 166 (3): 691–702. doi:10.1016/J.CELL.2016.06.020. ISSN   0092-8674. PMC   4967479 . PMID   27426948. Wikidata   Q34534392.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.