Domain of single-celled microorganisms with unique cell walls and membranes, distinct from bacteria and eukaryotes【182142013213942†L375-L411】
Explanation
Archaea are prokaryotic microorganisms that form a separate domain of life alongside Bacteria and Eukarya. Although archaeal cells resemble bacteria in lacking a nucleus and membrane-bound organelles, molecular studies revealed that their ribosomal RNA sequences and cellular chemistry are distinct. Archaeal cell walls do not contain peptidoglycan; instead they may be composed of pseudopeptidoglycan, polysaccharides, glycoproteins or pure protein【182142013213942†L375-L411】. Their cytoplasmic membranes are built from ether-linked lipids with isoprenoid chains, and some species form lipid monolayers rather than bilayers, enhancing stability at high temperatures【182142013213942†L389-L405】【182142013213942†L279-L283】. Archaeal genomes share features with eukaryotes, including similar transcription and replication proteins. These microorganisms reproduce by binary fission and display diverse morphologies from rods and cocci to square or filamentous forms. Many archaea are extremophiles that thrive in environments with high salt, acidity or temperature, but others inhabit soils, oceans and animal microbiomes. Metabolically, archaea can be chemoautotrophs, heterotrophs or methanogens, producing methane as a metabolic by-product.
Groups and habitats
Members of the Euryarchaeota include halophiles such as Halobacterium that inhabit hypersaline lakes and produce reddish blooms via light-driven proton pumps【182142013213942†L215-L220】. Methanogenic archaea are found in anaerobic sediments and animal guts, where they convert carbon dioxide and hydrogen into methane. Crenarchaeota comprise thermophilic and acidophilic species like Sulfolobus that grow at 75–80 °C and pH 2–3 near volcanic hot springs【182142013213942†L228-L234】. Nanoarchaeota have a single known representative, Nanoarchaeum equitans, an obligate symbiont isolated from hydrothermal vents【182142013213942†L239-L245】. Korarchaeota are primitive lineages detected only in hot springs at Yellowstone National Park【182142013213942†L253-L259】. More recently discovered phyla, such as Thaumarchaeota, include ammonia-oxidising archaea that contribute to nitrogen cycling in marine and soil ecosystems. Despite their ubiquity, no archaeon is currently known to cause disease in humans or animals; instead, they play essential roles in global biogeochemical cycles and are sources of enzymes used in biotechnology.
Archaea illustrate the diversity of microbial life and the importance of molecular evidence in understanding evolutionary relationships.
Related Terms: Bacteria, Eukaryotes, Extremophile, Methanogen, Prokaryote