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Archaea

The Archaea (/ɑrˈkiːə/ ( listen) ar-kee) are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). They have no cell nucleus or any other membrane-bound organelles within their cells.

In the past they had been classed with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this classification is regarded as outdated. In fact, the Archaea have an independent evolutionary history and show many differences in their biochemistry from other forms of life, and so they are now classified as a separate domain in the three-domain system. In this system, the phylogenetically distinct branches of evolutionary descent are the Archaea, Bacteria and Eukaryota.

Archaea are divided into four recognized phyla, but many more phyla may exist. Of these groups, the Crenarchaeota and the Euryarchaeota are the most intensively studied. Classification is still difficult, because the vast majority have never been studied in the laboratory and have only been detected by analysis of their nucleic acids in samples from the environment.

Archaea and bacteria are quite similar in size and shape, although a few archaea have very unusual shapes, such as the flat and square-shaped cells of Haloquadratum walsbyi. Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation. Other aspects of archaean biochemistry are unique, such as their reliance on ether lipids in their cell membranes. Archaea use a much greater variety of sources of energy than eukaryotes: ranging from familiar organic compounds such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no species of archaea is known to do both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no known species form spores.

Initially, archaea were seen as extremophiles that lived in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats, including soils, oceans, marshlands and the human colon. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are now recognized as a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle. No clear examples of archaeal pathogens or parasites are known, but they are often mutualists or commensals. One example is the methanogens that inhabit the gut of humans and ruminants, where their vast numbers aid digestion. Methanogens are used in biogas production and sewage treatment, and enzymes from extremophile archaea that can endure high temperatures and organic solvents are exploited in biotechnology.

For more information about Archaea, read the full article at Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.

Enzymatic synthesis of pyrrolysine, the mysterious 22nd amino acid

With few exceptions, all known proteins are built up from only twenty amino acids. 25 years ago scientists discovered a 21st amino acid, selenocysteine and ten years ago a 22nd, the pyrrolysine. However, how the cell produces ...

Chemistry / Biochemistry

created Nov 18, 2011 | popularity not rated yet | comments 0 | with audio podcast

Researchers map minority microbes in the colon

They make up less than one-hundredth of 1 percent of the microbes that live in the colon, but the bacteria and archaea that sop up hydrogen in the gut are fundamental to colon health. In a new study, researchers take a first ...

Biology / Cell & Microbiology

created Aug 02, 2011 | popularity 5 / 5 (2) | comments 1 | with audio podcast

Old life capable of revealing new tricks after all

(PhysOrg.com) -- Archaea are among the oldest known life-forms, but they are not well understood. It was only in the 1970s that these single-celled microorganisms were designated as a domain of life distinct ...

Biology / Cell & Microbiology

created Jul 06, 2011 | popularity 4.4 / 5 (7) | comments 0 | with audio podcast

Novel microorganism 'Nitrososphaera viennensis' isolated

Microorganisms play an important role in global nutrient cycles. A research team led by Christa Schleper, head of the Department of Genetics in Ecology at the University of Vienna, has isolated the first ammonium ...

Biology / Cell & Microbiology

created Apr 25, 2011 | popularity 5 / 5 (1) | comments 0 | with audio podcast

Weird, ultra-small microbes turn up in acidic mine drainage

(PhysOrg.com) -- In the depths of a former copper mine in Northern California dwell what may be the smallest, most stripped-down forms of life ever discovered.

Biology / Cell & Microbiology

created May 03, 2010 | popularity 4.9 / 5 (16) | comments 1

Scientists discover first multicellular life that doesn't need oxygen

(PhysOrg.com) -- Oxygen may not be the staple of modern complex life that scientists once thought. Until now, the only life forms known to live exclusively in anoxic conditions were viruses, bacteria and Archaea. ...

Biology / Plants & Animals

created Apr 07, 2010 | popularity 4.7 / 5 (73) | comments 15 | with audio podcast report

First volume of microbial encyclopedia published

The Earth is estimated to have about a nonillion (1030) microbes in, on, around, and under it, comprised of an unknown but very large number of distinct species. Despite the widespread availability of microbi ...

Biology / Cell & Microbiology

created Dec 23, 2009 | popularity 4.8 / 5 (6) | comments 0

Analysis knocks down theory on origin of cell structure

(PhysOrg.com) -- Understanding how living cells originated and evolved into their present forms remains a fundamental research area in biology, one boosted in recent years by the introduction of new tools ...

Biology / Cell & Microbiology

created Apr 22, 2009 | popularity 5 / 5 (7) | comments 0

Study of protein structures reveals key events in evolutionary history

A new study of proteins, the molecular machines that drive all life, also sheds light on the history of living organisms.

Biology / Biotechnology

created Mar 10, 2009 | popularity 4.8 / 5 (12) | comments 1