Related topics: bacteria

Scientists probe the role of archaea in the human microbiome

All multicellular living beings carry an unimaginably large number of microorganisms in and on their bodies. The microbiome, i.e. the totality of these microorganisms, forms a unit together with the host organism, the so-called ...

New insight into the evolution of complex life on Earth

A novel connection between primordial organisms and complex life has been discovered, as new evidence sheds light on the evolutionary origins of the cell division process that is fundamental to complex life on Earth.

An open-source data platform for researchers studying archaea

Bioinformatics and big data analyses can reap great rewards for biologists, but it takes a lot of work to generate the datasets necessary to begin. At the same time, researchers around the globe churn out datasets that could ...

New ethane-munching microbes discovered at hot vents

Researchers from the Max Planck Institute for Marine Microbiology in Bremen have discovered a microbe that feeds on ethane at deep-sea hot vents. With a share of up to 15%, ethane is the second-most common component of natural ...

A light driven proton pump in distant relative

Researchers investigated the group of microorganisms classified as Asgard archaea, and found a protein in their membrane which acts as a miniature light-activated pump. The schizorhodopsin protein draws protons into the organisms' ...

Solved: Mystery of marine nitrogen cycling in shelf waters

Nitrogen cycling in shelf waters is crucial to reduce surplus nutrients, which rivers pour out into the ocean. Yet this process is poorly understood. Scientists from Bremen have now found answers to a longstanding mystery ...

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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with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this classification is regarded as outdated.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.

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