archaéában

Archaea are a domain of single-celled microorganisms that form one of the three domains of life, alongside Bacteria and Eukarya. Like bacteria, archaea are prokaryotes, meaning they lack a membrane-bound nucleus, but they differ in many fundamental features of biochemistry and genetics. Discovered through 16S rRNA analysis in the 1970s, they were initially grouped with bacteria as "archaebacteria" before being reclassified as a separate domain.

Archaea have distinctive cell membranes built from ether-linked lipids with isoprenoid chains, and most lack peptidoglycan in their cell walls. Their transcription and replication systems show closer similarity to those of eukaryotes than to bacteria. Archaea inhabit a wide range of environments, from oceans and soils to the guts of animals. Although many are extremophiles—thermophiles at high temperatures, halophiles at high salinity, or acidophiles in acidic waters—others live in moderate conditions and are common in many ecosystems.

Ecologically, archaea contribute to key biogeochemical cycles. Methanogens convert carbon dioxide and hydrogen into methane in anaerobic environments, shaping methane fluxes; ammonia-oxidizing Thaumarchaeota influence nitrogen cycling; and archaeal communities are abundant in marine and terrestrial ecosystems. In humans and other animals, archaea form part of the microbiome, though their roles are still being explored.

Taxonomically, several major archaeal phyla are recognized, including Euryarchaeota, Crenarchaeota, Thaumarchaeota, Korarchaeota, and Nanoarchaeota, among others. The domain is the subject of ongoing research, with new lineages and metabolic pathways continually discovered as sequencing technologies advance.