Related topics: bacteria

Marine extremophiles: The basal level of the food chain

In nutrient-poor deep-sea sediments, microbes belonging to Archaea have outcompeted bacterial microorganisms for millions of years. Efficiently scavenging dead cells makes them the basal producers in the food chain.

The expanding universe of methane metabolisms in archaea

Methane is a greenhouse gas 20 times more potent than carbon dioxide. Billions of years ago, methane-producing archaea likely played a key role in determining the composition of the Earth's atmosphere and regulating the global ...

New key players in the methane cycle

Methane is not only a powerful greenhouse gas, but also a source of energy. Microorganisms therefore use it for their metabolism. They do so much more frequently and in more ways than was previously assumed, as revealed by ...

Biology of our ancient ancestor takes shape

The recent discovery of a new lineage of microbes has overturned biologists' understanding of the evolution of complex life on Earth. Genomic studies of Asgard archaea revealed that they carry many genes previously thought ...

Key players in the marine nitrogen cycle use cyanate and urea

The ammonia oxidizing archaea, or Thaumarchaeota, are among the most abundant marine microorganisms. Yet, scientists are still discovering which factors allow them to thrive in the ocean. A research team from the Max Planck ...

A microbe's membrane helps it survive extreme environments

Within harsh environments like hot springs, volcanic craters and deep-sea hydrothermal vents – uninhabitable by most life forms – microscopic organisms are thriving. How? It's all in how they wrap themselves.

Getting out of hot water—does mobile DNA help?

Extremophiles—hardy organisms living in places that would kill most life on Earth—provide fascinating insights into evolution, metabolism and even possible extraterrestrial life. A new study provides insights into how ...

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with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this classification is regarded as outdated.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

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