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Halobacteria sp. strain NRC-1

The Archaea are a group of single-celled microorganisms with no cell nucleus nor any other membrane-bound organelles. They show many differences in their biochemistry from other forms of life and have an independent evolutionary history. In the three-domain system, they are classified as a separate domain from the phylogenetically distinct 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 most intensively studied. Classification is still difficult, since the vast majority have never been studied in the laboratory. Archaea and bacteria are quite similar in size and shape, but a few archaea have very unusual shapes. 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. 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, and marshlands. 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. (more...)

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