archaeon

An archaeon is a single organism that belongs to the domain Archaea, a distinct lineage of life separate from Bacteria and Eukaryota. Archaea are prokaryotic, meaning they lack a nucleus, but they are not bacteria. They inhabit a wide range of environments, including oceans, soils, hot springs, salt lakes, acidic environments, and even the human body.

Discovery and classification: The domain Archaea was established in the 1970s after researchers led by Carl Woese showed that certain prokaryotes differed markedly from bacteria in their ribosomal RNA sequences. This revealed a distinct lineage, reconfiguring the tree of life to include Archaea as one of its primary domains.

Cell structure and genetics: Archaeal cells typically have ether-linked lipids in their membranes and often lack peptidoglycan in their cell walls, sometimes enclosing their cells with S-layers or pseudopeptidoglycan. Their transcription and translation systems share features with eukaryotes, such as a multi-subunit RNA polymerase and histone-like proteins, even though archaea are prokaryotes in overall cellular organization. Metabolic pathways are diverse and adapted to extreme or nutrient-poor environments in many species.

Metabolism and ecology: Archaea exhibit a broad spectrum of lifestyles. Methanogens produce methane in anaerobic conditions and are important in carbon cycling. Halophiles thrive in high-salt environments, thermophiles in high temperatures, and acidophiles in low pH. Many archaea form symbiotic relationships and contribute to nutrient turnover in soils, sediments, and aquatic systems.

Significance: Studying archaea sheds light on the evolution of life and the origins of eukaryotes. Archaeal enzymes are valued for industrial applications due to their stability under extreme conditions, and archaea are increasingly recognized for their roles in human health and environmental processes.