Arkæer

Archaea
Archaea
	Halobacteria
Videnskabelig klassifikation
Overdomæne	Biota
Domæne	Archaea; Woese, Kandler; & Wheelis, 1990
	Hjælp til læsning af taksobokse

Arkæerne (latin Archaea, fra græsk ἀρχαία, "de gamle") er et af de tre domæner af levende organismer sammen med bakterier og eukaryoter. Arkæer og bakterier kaldes samlet for prokaryoter^[1] (fra pro- og græsk karyon,^[2] "for, foran, frem, fremad, før kerne").^[3] Arkæernes separate identitet blev opdaget i 1970'erne af Dr. Carl Woese fra University of Illinois ved hjælp af genetisk sammenligning. Oprindeligt blev arkæerne benævnt arkebakterier, mens de andre prokaryote blev benævnt eubacteria (ægte bakterier). Der er dog en stigende tendens til at indskrænke termen eubacteria til bakterie. Arkæerne kan behandles som et enkelt rige eller et domæne.

Arkæerne adskiller sig fra de ægte bakterier på mange vigtige punkter:

Vægstruktur og kemi.
Den lipide membranstruktur.
metabolisme (metanædere, sulfat reducerende...).

Mange arkæer er ekstremofile og lever i ekstreme miljøer, herunder ved temperaturer, der overstiger kogende vands, fx i gejsere, meget saltet vand samt surt eller alkalisk vand. Arkæerne lever fx ved hydrotermiske væld^[4] og får fx energi ved at oxidere vældets sorte røg og er dermed kemoautotrof. De lever også ved varme kilder – fx Yellowstone National Parks varme kilder, hvor de først blev opdaget – og vulkanske sprækker.^[5] Man har også fundet DNA-rester, som peger på, at der lever arkæer ved Atacama-vulkaner, hvilket er et miljø, der er tæt på det, man finder på Mars'.^[6] Andre er fundet i en isoleret sø 800 m under iskappen på Antarktis.^[7]^[8] Arkæerne har en stor diversitet i både morfologi og fysiologi.

Noget forskning tyder på, at Euryarchaeota er tættere på eukaryote end på Crenarchaeota. Er dette tilfældet, vil riget Archaea blive opgivet. Mikrobiologer, som anser bakterier for at være parafyletiske, argumenterer også med, at arkæer ikke er tilstrækkeligt forskellige fra bakterier til at blive betragtet som en separat gruppe.

Det er blevet påvist, at visse arkæer spiser/omsætter metangas fra havvand i dybhavet og dermed mindsker den mængde metan, som ellers ville være havnet i atmosfæren. Disse arkæer spises/"græsses" af orme i dybhavet ud for bl.a. Costa Rica og USAs vestkyst. Det er første gang, at arkæer er påvist at være en del af en fødekæde. Organismer, som spiser arkæer, foreslås at kaldes "archivory" af Thurber. ^[9]

Domæne Arkæer, Archaea (methanogener, halophiler, sulfolobus...)
- Rige Arkebakterier, Archebacteria

Klassifikation

Domæne: Archaea

Række: Crenarchaeota
- Klasse: Thermoprotei
  - Orden: Thermoproteales
  - Orden: Desulfurococcales
  - Orden: Sulfolobales
Række: Euryarchaeota
- Klasse: Methanobacteria
  - Orden: Methanobacteriales
- Klasse: Methanococci
  - Orden: Methanococcales
  - Orden: Methanomicrobiales
  - Orden: Methanosarcinales
- Klasse: Halobacteria
  - Orden: Halobacteriales
- Klasse: Thermoplasmata
  - Orden: Thermoplasmatales
- Klasse: Thermococci
  - Orden: Thermococcales
- Klasse: Archaeoglobi
  - Orden: Archaeoglobales
- Klasse: Methanopyri
  - Orden: Methanopyrales
Række: Nanoarchaeota
- Slægt: Nanoarchaeum
  - Nanoarchaeum equitans

Kilder/referencer

^ L. Margulis, Schwartz, K.V. (1988). Five Kingdoms, An Illustrated Guide to the Phyla of Life on Earth, 2nd Edition (engelsk). W.H. Freeman and Company. s. 24. ISBN 0-7167-1912-6.{{cite book}}: CS1-vedligeholdelse: Flere navne: authors list (link)
^ "prokaryot" i Den Store Danske. Hentet 9. august 2019.
^ "pro-" i Den Store Danske. Hentet 9. august 2019.
^ The American Museum of Natural History: Deep sea hydrothermal animals Citat: "...Archaea...get their energy by oxidizing the minerals in the black smoke..."
^ berkeley.edu: Introduction to the Archaea: Life's extremists... Citat: "...Some live near rift vents in the deep sea at temperatures well over 100 degrees Centigrade. Others live in hot springs (such as the ones pictured above), or in extremely alkaline or acid waters. They have been found thriving inside the digestive tracts of cows, termites, and marine life where they produce methane. They live in the anoxic muds of marshes and at the bottom of the ocean, and even thrive in petroleum deposits deep underground..."
^ University of Colorado at Boulder (2012, June 8). Microbes discovered in extreme environment on South American volcanoes. ScienceDaily Citat: "...How the newfound organisms survive under such circumstances remains a mystery...Atacama volcanoes are some of the most similar places on Earth to the Red Planet [Mars]..."
^ * Cold, Dark and Alive! Life Discovered in Buried Antarctic Lake. Livescience, august 2014
^ The mysterious microbes that gave rise to complex life. Nature News Feature 2021
^ Oregon State University (2012, March 12). First consumption of abundant life form, Archaea, discovered. ScienceDaily Citat: "...Archaea that consume the greenhouse gas methane were in turn eaten by worms living at deep-sea cold seeps off Costa Rica and the West Coast of the United States. Archaea perform many key ecosystem services including being involved with nitrogen cycling, and they are known to be the main mechanism by which marine methane is kept out of the atmosphere...The consumption of Archaea by grazers, a process coined "archivory" by Thurber in the article..."

Se også

Eksterne henvisninger

Strange life form found in ocean Citat: "...Named Nanoarchaeum equitans, the spherical bugs live on the surface of a much bigger Archael organism, Ignicoccus...."
BBC News July 21, 1999: Toughest bug reveals genetic secrets Citat: "...It [Pyrococcus abyssi] likes conditions that the vast majority of other organisms would find impossible to live in. It thrives best at temperatures of about 103 degrees Centigrade and under pressures of about 200 atmospheres..."
Pyrococcus abyssi Home page at Genoscope

[1] L. Margulis, Schwartz, K.V. (1988). Five Kingdoms, An Illustrated Guide to the Phyla of Life on Earth, 2nd Edition (engelsk). W.H. Freeman and Company. s. 24. ISBN 0-7167-1912-6.{{cite book}}: CS1-vedligeholdelse: Flere navne: authors list (link)

[2] "prokaryot" i Den Store Danske. Hentet 9. august 2019.

[3] "pro-" i Den Store Danske. Hentet 9. august 2019.

[4] The American Museum of Natural History: Deep sea hydrothermal animals Citat: "...Archaea...get their energy by oxidizing the minerals in the black smoke..."

[5] rkeley.edu: Introduction to the Archaea: Life's extremists... Citat: "...Some live near rift vents in the deep sea at temperatures well over 100 degrees Centigrade. Others live in hot springs (such as the ones pictured above), or in extremely alkaline or acid waters. They have been found thriving inside the digestive tracts of cows, termites, and marine life where they produce methane. They live in the anoxic muds of marshes and at the bottom of the ocean, and even thrive in petroleum deposits deep underground..."

[6] University of Colorado at Boulder (2012, June 8). Microbes discovered in extreme environment on South American volcanoes. ScienceDaily Citat: "...How the newfound organisms survive under such circumstances remains a mystery...Atacama volcanoes are some of the most similar places on Earth to the Red Planet [Mars]..."

[7] * Cold, Dark and Alive! Life Discovered in Buried Antarctic Lake. Livescience, august 2014

[8] The mysterious microbes that gave rise to complex life. Nature News Feature 2021

[9] Oregon State University (2012, March 12). First consumption of abundant life form, Archaea, discovered. ScienceDaily Citat: "...Archaea that consume the greenhouse gas methane were in turn eaten by worms living at deep-sea cold seeps off Costa Rica and the West Coast of the United States. Archaea perform many key ecosystem services including being involved with nitrogen cycling, and they are known to be the main mechanism by which marine methane is kept out of the atmosphere...The consumption of Archaea by grazers, a process coined "archivory" by Thurber in the article..."

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