Discoba je grupa bičastih protista koji čine glavni dio supergrupe Excavata.[1] Većina podskupina su dvobičaši, aerobi, slobodnoževeći u slatkoj ili morskoj vodi, sa citosomom za unos (uglavnom) bakterija. Izuzetak je Euglenophyceae, skupina zelenih mikroalgi koje su stekle fotosintetski metabolizam. Druga posebna skupina je Percolozoa, koja ima tri životna stadija: bičasti, cista i ameboid, ovisno o dostupnosti hrane. Postoje i neki primjeri parazita koji uzrokuju bolesti protozojskog porijekla kao što je Trypanosoma. Predačko obilježje je ventralni žlijeb za unošenje hrane, kao i u Excavata, što se vidi i u baznim skupinama, koje su sa dva biča. Ponekad postoje multiflagelatni oblici, poput roda Stephanopogon.
Discoba je robusna skupina sastavljena na osnovu multigenih filogenetskih analiza; sadrži Percolozoa (= Heterolobosea), Euglenozoa, Jakobea i od nedavno Tsukubamonas.[2] Definirana je kao kladus sastavljen od najnovijeg pretka sličnog akoba libera , Andalucia godoyi, Euglena gracilis i Naegleria gruberi.[3]
Holomycota → ([L] Fungi)
[B] Excavata (Parafilija?)Discoba
Značajnije promjene u filogenezi eukariota:
[A] Eukariotski, heterotrofni predački bičari,
[B] Žljeb za dovod hrane
[C] Heterokontni bič
[D] Korteksne alveole
[E] Filipodije
[F] Haptonema i aksopodije
[G] Dodaci prednjem biču
[H] Pojava hloroplasta od primarne endosimbioze Cyanobacteria
[I] Trostruka fuzija gena za biosintezu pirimidina.
[J] Lobopodije
[K] Zadnji bič
[L] Hitin
[M] Kolagen, Blastulacija i diferencijacija tkiva
Discoba je grupa bičastih protista koji čine glavni dio supergrupe Excavata. Većina podskupina su dvobičaši, aerobi, slobodnoževeći u slatkoj ili morskoj vodi, sa citosomom za unos (uglavnom) bakterija. Izuzetak je Euglenophyceae, skupina zelenih mikroalgi koje su stekle fotosintetski metabolizam. Druga posebna skupina je Percolozoa, koja ima tri životna stadija: bičasti, cista i ameboid, ovisno o dostupnosti hrane. Postoje i neki primjeri parazita koji uzrokuju bolesti protozojskog porijekla kao što je Trypanosoma. Predačko obilježje je ventralni žlijeb za unošenje hrane, kao i u Excavata, što se vidi i u baznim skupinama, koje su sa dva biča. Ponekad postoje multiflagelatni oblici, poput roda Stephanopogon.
Discoba je robusna skupina sastavljena na osnovu multigenih filogenetskih analiza; sadrži Percolozoa (= Heterolobosea), Euglenozoa, Jakobea i od nedavno Tsukubamonas. Definirana je kao kladus sastavljen od najnovijeg pretka sličnog akoba libera , Andalucia godoyi, Euglena gracilis i Naegleria gruberi.
Jakobea es un classe de Excavata, Discoba.
Jakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small (less than 15 μm), and can be found in aerobic and anaerobic environments.[3][4][5] The order Jakobida, believed to be monophyletic, consists of only twenty species at present, and was classified as a group in 1993.[3][5][6] There is ongoing research into the mitochondrial genomes of jakobids, which are unusually large and bacteria-like, evidence that jakobids may be important to the evolutionary history of eukaryotes.[4][7]
Molecular phylogenetic evidence suggests strongly that jakobids are most closely related to Heterolobosea (Percolozoa) and Euglenozoa.[8]
Jakobids have two flagella, inserted in the anterior end of the cell, and, like other members of order Excavata, have a ventral feeding groove and associated cytoskeleton support.[9] The posterior flagella has a dorsal vane and is aligned within the ventral groove, where it generates a current that the cell uses for food intake.[7] [9] The nucleus is generally in the anterior part of the cell and bears a nucleolus. Most known jakobids have one mitochondrion, again located anteriorly, and different genera have flattened, tubular, or absent cristae. Food vacuoles are mostly located on the cell posterior, and in most jakobids the endoplasmic reticulum is distributed throughout the cell.[6]
The sessile, loricate Histionidae and occasionally free-swimming Jakoba libera (Jakobidae) have extrusomes under the dorsal membrane that are theorized to be defensive structures.[3][6]
Jakobids are widely dispersed, having been found in soil, freshwater, and marine habitats, but generally not common.[4][7][6][10] However, environmental DNA surveys suggest that Stygiellidae are abundant in anoxic marine habitats.[6][11] Some are capable of surviving hypersaline and anoxic environments, though the Histionids have only been found in freshwater ecosystems, where they attach themselves to algae or zooplankton.[6] Outside of obligate sessile species, many species of jakobids can attach temporarily to surfaces, using either of the two flagella or the cell body itself.[11]
All known jakobids are heterotrophic suspension feeders.[4][6] Their primary prey is generally considered to be bacteria, though one species has been observed eating extremely small (< 1 µm) eukaryotic cells.[5][12] Jakobids are generally slow swimmers, with low clearance rates relative to similar organisms.[6]
No study has suggested jakobids might be pathogenic or toxic.[6]
Since jakobids have no current commercial use, most research into jakobids has focused on their evolutionary significance. The mitochondrial DNA of jakobids is the most bacteria-like of all known eukaryotic mitochondrial DNA, suggesting that jakobid mitochondrial genomes might approximate the ancestral mitochondrial genome.[6]
Jakobid mitochondrial DNA is substantially different from most other eukaryotes, especially in terms of the number of genes (nearly 100 in some species) and bacteria-like elements within their genomes.[5][6] Nine of the genes have never been found in eukaryotic mitochondrial DNA. Uniquely, jakobid mitochondrial genomes code for bacteria-type RNA polymerase, as opposed to typical eukaryotic mitochondrial RNA polymerase, referred to as “phage-type”, which appears to be viral in origin.[6] This does not necessarily mean that jakobids are basal to the phylogeny of eukaryotes. While jakobid mitochondria have genetic features that seem to have developed from bacteria, and apparently lack phage-type RNA, it is possible that other eukaryotic clades lost their bacterial features independently.[13]
Several proposed possibilities might explain the bacterial features of jakobid mitochondrial DNA. One is that jakobids diverged very early from the rest of the eukaryotes. This hypothesis depends on whether or not jakobids are indeed basal to all living eukaryotes, but there is no evidence yet to support that suggestion.[6]
Another hypothesis is that the phage-type RNA polymerase moved from one eukaryote group to another via lateral gene transfer, replacing the bacteria-type enzyme, and simply did not reach the jakobids. This would not depend on jakobids being basal to eukaryotes as a whole, but has not been widely studied.[6]
A third possibility is the reverse of the others, suggesting that the phage-type RNA polymerase is the basal one. Under this scenario, jakobids acquired their bacteria-type RNA polymerase much more recently and that then spread via lateral gene transfer.[6] However, the gene arrangement of jakobid mitochondrial DNA suggests an ancestral origin of bacteria-type RNA polymerase over a more-recent divergence.[5][6]
One of the proposed scenarios suggests that the common ancestor of eukaryotes had two mitochondrial RNA polymerases, both phage-type and bacteria-type, and jakobids lost their phage-type polymerase while the rest of the eukaryotes lost the bacteria-type, possibly several times.[6][14] Such a model eliminates the need for jakobids to be truly basal. One study proposed that the phage-type and bacteria-type polymerases, when present in the same mitochondrion, served different functions, much in the way that the organelles of land plants have two different RNA polymerase enzymes that transcribe different genes.[6]
Jakobida contains five families consisting of mostly free-swimming genera: Jakobidae, Moramonadidae, Andaluciidae, and Stygiellidae.[6] The sixth family, Histionidae, is largely populated by sessile loricate genera, and includes the first jakobids ever described.[6]
Jakobids are a monophyletic group, and are most closely related to the Euglenozoa and Heterolobosea.[5][6][13]
Cladogram of Jakobida[15] Ophirinina Ophirinidae Andaluciina Andaluciidae Stygiellidae Histionina Moramonadidae Jakobidae HistionidaeJakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small (less than 15 μm), and can be found in aerobic and anaerobic environments. The order Jakobida, believed to be monophyletic, consists of only twenty species at present, and was classified as a group in 1993. There is ongoing research into the mitochondrial genomes of jakobids, which are unusually large and bacteria-like, evidence that jakobids may be important to the evolutionary history of eukaryotes.
Molecular phylogenetic evidence suggests strongly that jakobids are most closely related to Heterolobosea (Percolozoa) and Euglenozoa.
Jakobea o Jakobida es un pequeño grupo de protistas flagelados, heterótrofos y de vida libre, que comprende una docena de especies de agua dulce o marinas.[2] Se incluyen en el clado Excavata, junto con otros organismos flagelados similares.[3][4]
Solo existen una docena de especies descritas de este grupo, el cual no fue reconocido como tal hasta principios de los años 90 y no habían sido bien estudiados hasta que se descubrió que su genoma mitocondrial puede ser utilizado como una posible evidencia de la teoría de endosimbiosis.
Generalmente, los Jakobida miden menos de 15 micras, presentan un surco ventral de alimentación y dos flagelos, característicos de los excavados. La acción de los flagelos genera corrientes de agua que utilizan para capturar el alimento, debido al movimiento de éstos generan corriente que mueven partículas suspendidas hacia el interior del surco para su posterior fagocitación.[5]
Las especies nadadoras de vida libre han sido encontradas en una amplia gama de ambientes incluyendo agua dulce, salada, suelo e incluso en hábitats hipersalinos. En contraste, las especies sésiles solo han sido encontradas en hábitats de agua dulce.[6]
La mitocondria de los organismos eucariota, de acuerdo a la teoría endosimbiótica, deriva de una bacteria que entabló una relación simbiótica con células más desarrolladas. El genoma mitocondrial es un remanente reducido del genoma de la bacteria simbiótica, y por esto, son genomas muy pequeños en la mayoría de los eucariota. Jakobida es una excepción, debido a que su genoma mitocondrial contiene más genes funcionales que los demás organismos, conservando muchas características idénticas al genoma de las proteobacterias alfa que dieron origen a las mitocondrias, esto representa un gran interés evolutivo y una fuerte evidencia que apoya la teoría endosimbiótica de Lynn Margullis.
Jakobea comprende cuatro familias distribuidas entre dos subórdenes:
Jakobea forma parte del clado Discoba, un robusto subgrupo de Excavata constituido sobre la base de análisis filogenéticos multigen, que contiene a Percolozoa (=Heterolobosea), Euglenozoa, Jakobea y recientemente Tsukubamonas.[7][8] Un taxón relacionado, Loukozoa, ha sido continuamente redefinido para incluir a una gran variedad de grupos (entre ellos Jakobida y Malawimonas) y finalmente abandonado.[9] Recientemente Loukozoa ha sido recuperado por Cavalier-Smith para englobar a los excavados primitivos que no pueden ser clasificados en los grupos principales (es un grupo parafilético).[10]
Jakobea o Jakobida es un pequeño grupo de protistas flagelados, heterótrofos y de vida libre, que comprende una docena de especies de agua dulce o marinas. Se incluyen en el clado Excavata, junto con otros organismos flagelados similares.
Solo existen una docena de especies descritas de este grupo, el cual no fue reconocido como tal hasta principios de los años 90 y no habían sido bien estudiados hasta que se descubrió que su genoma mitocondrial puede ser utilizado como una posible evidencia de la teoría de endosimbiosis.
Les Jakobea constituent un embranchement des Excavata et sa seule classe.
Les Jakobea constituent un embranchement des Excavata et sa seule classe.
Discoba é um agrupamento taxonómico de protistas incluído noclade Excavata,[1] constituído com base em resultados robustos de análises filogenéticas multigene, que contém os grupos Percolozoa (=Heterolobosea), Euglenozoa, Jakobea e, recentemente, Tsukubamonas.[2]
Do ponto de vista da filogenética o agrupamento Discoba é definido como o clade constituído a partir do antepassado comum mais recente de Jakoba libera, Andalucia godoyi, Euglena gracilis e Naegleria gruberi.[3]
Discoba é um agrupamento taxonómico de protistas incluído noclade Excavata, constituído com base em resultados robustos de análises filogenéticas multigene, que contém os grupos Percolozoa (=Heterolobosea), Euglenozoa, Jakobea e, recentemente, Tsukubamonas.
Протисти завдовжки до 15 мкм. Вони мають два джгутика з однієї сторони. Один з джгутиків пов'язаний з борозенкою, яка займає більшу частину однієї сторони клітини. Ця борозна призначена для живлення, а рух джгутика створює потік рідини з органічними частинками. Інший джгутик призначений для руху клітини.[1]
Більшість видів вільно плавають у субстраті, деякі види можуть тимчасово прикріплюватися до дна джгутиком. Reclinomonas і Histionas більшу частину життя проводять у сидячому стані у спеціальних туніках (Lorica). Jakobida знайдені у різних середовищах: морських, прісноводних, на ґрунті, у гіперсолених водоймах. Сидячі форми відомі лише у прісних водоймах.[1]
Порядок включає 5 родин:
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Це незавершена стаття про найпростіших.
자코바류(Jakobids)는 엑스카바타계에 속하는 원생생물 분류군이다. 자코바강(Jakobea)의 유일한 목이다. 분자생물학상의 계통분류학적인 증거를 통해, 자코바목은 이엽상근족충류(Heterolobosea)(=페르콜로조아)와 유글레나류와 가장 밀접한 관계에 있음이 밝혀졌다.[1]
