Characteristics of archaea
Inhabitants of domain Archaea are more closely related to eukaryotic cells than they are to bacteria. Whereas both bacteria and archaea lack a nuclear envelope and membrane-bound organelles, archaea and eukaryotes have similarities beyond those seen between bacteria and eukaryotic cells. Bacteria have the macromolecule peptidoglycan in their cell walls; archaea and eukarya lack this polymer. Bacteria have only a single kind of RNA polymerase, whereas archaea and eukaryotes have several kinds. Introns and DNA-associated histone proteins—a defining characteristic of eukaryotic cells—are absent (histones) or rarely seen (introns) in bacteria but are present in some archaea species.
Activities of archaea
Domain Archaea contains some prokaryotic cells that live in conditions that are too extreme for other forms of life. Thermophiles thrive at temperatures as hot as 90°C and are found in deep-sea volcanic vents and hot springs. These prokaryotes have evolved to withstand temperatures that would otherwise kill cells by denaturing DNA and proteins. The biotechnological method of polymerase chain reaction (PCR) is possible because of the heat-tolerant DNA polymerase isolated from a thermophile. The extreme halophiles withstand highly saline conditions such as the Great Salt Lake and the Dead Sea.
Not all archaea are extremophiles, however; many live in more moderate environments. Methanogens are found in many diverse niches, including swamps, termite and cow guts, and deep-sea hydrothermal vents. Methanogens are strict anaerobes that cannot tolerate oxygen. They generate energy using CO2 to oxidize H2, creating CH4 (methane) as a waste product. Methanogens play an important role in water remediation in sewage treatment facilities due to their ability to anaerobically decompose organic waste matter.