euryarchaeotes

Euryarchaeota is a major phylum of the domain Archaea. Members display extensive metabolic diversity, including methane production, anaerobic respiration, and extreme halophily. They inhabit a wide range of environments, from anaerobic sediments and the guts of ruminants to hypersaline lakes, acidic hot springs, and hydrothermal habitats. In older literature, these organisms were often referred to as euryarchaeotes; the current designation is Euryarchaeota.

Methanogens are a prominent and defining group within Euryarchaeota. These strictly anaerobic archaea generate methane as a metabolic end product by reducing carbon compounds such as CO2, acetate, or methylated substrates. They play critical roles in carbon cycling and are found in wetlands, the digestive tracts of ruminants and termites, and in anaerobic digesters used for waste treatment and biogas production.

Halophiles constitute another well-known group, adapted to high-salt environments. Many require several molar concentrations of NaCl for growth and accumulate compatible solutes or salts to balance osmotic pressure. Some halophilic archaea possess light-driven proton pumps such as bacteriorhodopsin and pigmentation that can give pink to purple appearances; they are common in salt lakes, brines, and saline soils.

Among the other lineages, Thermoplasmata include thermoacidophilic archaea such as Thermoplasma and Ferroplasma, many of which lack a rigid cell wall and thrive in acidic, high-temperature habitats. Archaeoglobi are hyperthermophilic, sulfate-reducing archaea that occur in volcanic rocks, hydrothermal systems, and other anaerobic, high-temperature environments.

Taxonomically, Euryarchaeota encompasses several major classes and orders and is distinguished from other archaeal phyla by its metabolic breadth. Its members contribute to methane production, sulfur and metal cycling, and biotechnological applications in waste treatment and industry.