Domain Archaea

The Archaea are a newly discoverd domain of life on earth, originally thought to be a subset of Bacteria. Archaea are microscopic, single-celled organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles.

While archaea and bacteria look similar in structure, they have very different metabolic and genetic activity. Archaea differ biochemically from the bacteria in the arrangement of the bases in their ribosomal RNA and in the composition of their plasma membranes and cell walls. In these respects they are more closely related to the Eukarotes than to the Bacteria.

Another defining physiological characteristic of archaea is their ability to live in extreme conditions. They are often called extremophiles and unlike the bacteria and eukarya depend on either high salt, high or low temperature, high pressure, or high or low pH.

Some believe the Archaea are ancient, since they live in harsh environments that resemble conditions existing when the earth was young. (The hyperthermophiles represent a living example of some of Earth's earliest organisms, located at the base of the Archaea.)

The Archaea possess unique membrane lipids, which are ether-linked glycerol derivatives of 20 or 40 carbon branched lipids. The lipids' unsaturations are generally conjugated (as opposed to the unconjugation found in Bacteria and Eukaryota).

These unusual properties of Crenarchaeota have attracted the attention of a wide range of scientists, including evolutionary biologists, exobiologists and biotechnology companies. The extreme conditions under which Crenarchaeota live today may be similar to those which existed on the early Earth at the time that life first arose. This, together with information about their geneology, suggests that these organisms may be much like the earliest lifeforms on earth. Photographs of some regions of the surface of Mars suggest that large hot spring systems, perhaps containing microbial life, may have once existed there. As a result, NASA exobiologists may study these features for chemical and fossil remnants of organisms resembling Crenarchaeota.