Recent investigations have led to the recognition that a group of prokaryotic organisms, the Archaea, are distinct from the Bacteria. Archaea, like bacteria, do not have cell nuclei or other membrane-bound organelles. However, the Archaea do possess several features that are shared with Eukarya, such as histone proteins and some other molecular characteristics. In other ways the Archaea are unique. For instance, the membrane lipids of Archaea are ether-linked rather than the familiar ester-linked phospholipids of both Bacteria and Eukarya.
Archaea are also noteworthy because they inhabit extreme environments such as high temperature, high salinity, acid, or some combination of these conditions. In addition, some Archaea are methanogenic, meaning that they produce methane gas. Archaea could be useful for the production of enzymes that can be used a high temperatures or for the production of methane as an energy source.
Until very recently the Archaea were referred to as "Archaebacteria". The name was changed to clearly indicate the fundamental differences between Archaea and Bacteria.
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Few general references or links are currently available on the Archaea. However, more information and links to some images can be found at the University of California at Berkeley Museum of Paleontology. A really good set of on-line lecture notes on Microbial Diversity has a lot of information on Archaea. "Popular" science articles on Archaea can be found at Breakthrough and Brave New Biosphere. A short discussion of research on methanogenic Archaea can be found at the University of Nijmegen (the Netherlands). A really wonderful site with lots of information on hot spring organisms in general is Life at High Temperatures.
