archaea

Archaea are a domain of single-celled microorganisms that constitute one of the three domains of life, alongside Bacteria and Eukarya. Like bacteria, archaea are prokaryotes: they generally lack a membrane-bound nucleus and other organelles. Their cells are usually small and simple in structure, but their biochemistry differs in important ways. Archaea have cell membranes built from ether-linked lipids and often with a lipid monolayer in some extremophiles, which helps them endure harsh conditions. Their cell walls rarely contain peptidoglycan; many archaeal species possess pseudopeptidoglycan or an S-layer.

Archaea occupy a wide range of habitats, from extreme environments such as hot springs, acidic waters, and hypersaline lakes to soils, oceans, and animal guts. They display diverse metabolic strategies, including methanogenesis (the production of methane in anaerobic environments), sulfate and nitrite reduction, and ammonia oxidation. Methanogens are unique to archaea and are major contributors to methane cycling. Some archaea form symbiotic associations with other organisms.

In terms of genetics and evolution, archaea are more closely related to eukaryotes at the level of transcription and translation; their RNA polymerases resemble eukaryotic enzymes, and some species possess histone-like proteins. Genome analyses reveal a mosaic of archaeal and bacterial genes, reflecting extensive horizontal gene transfer through deep time. Archaea reproduce asexually by binary fission, budding, or fragmentation.

Archaea play essential roles in global biogeochemical cycles and have biotechnological importance. Enzymes from archaea are often highly stable and useful in industrial processes; research on archaea has also contributed to understanding the evolution of complex cellular life, including the origin of eukaryotes.