The Archaea are a group of prokaryotes (cells that lack nuclei and other organelles) that were first discovered in extreme environments such as hot springs, acid waters and hypersaline ponds. In fact, one archaeal species found in deep sea hydrothermal vents, Pyrolobus fumarii, holds the current record for living at the hottest temperatures, with optimal growth at 106 °C, and survival of up to an hour of autoclaving. Genetic and subsequent biochemical analyses of this group showed that Archaea differ greatly from other microbes, and they are now classified as the third kingdom or “ domain ” of life, along with Bacteria (or Eubacteria) and Eukarya (cells with nuclei).
Left: Analysis of the ribosomal RNA gene revealed that the Archaea represent branch of life that is genetically distinct from Eukaryotes (including us) and Bacteria (reproduced from this website). Right: Subsequent biochemical and molecular studies showed a wide range of differences between the Archaea and the other domains, including the structure of the cell wall. Some Archaea have a peptidoglycan called pseudomurein which resembles the cell walls of Bacteria, while others have a surface layer (S-layer) that consists of repeating units of proteins, glycoproteins
or sugar (from this website)
More recent research in environmental microbiology has shown that many Archaea also abundant and surprising diverse in non-extreme environments such as soils, freshwaters and the sea. The huge methane output from rice field soils appears to be largely due to a phylogenetic cluster of archaeal methanogens, and ammonium oxidation (the first step of nitrification) in soils and the ocean may be mostly conducted by certain Archaea. In the northern environment, Archaea have been found to be a common constituent of the coastal Arctic Ocean, especially in particle-rich waters (Wells et al. 2006; Garneau et al. 2006). In the Mackenzie River, a large arctic river in northwest Canada, molecular analyses show the presence of more than 250 genetically distinct Archaea, perhaps reflecting the diversity of substrates in the river, and its diversity of source waters (Galand et al. 2006).
Wells, L.E., Cordray, M., Bowerman, S., Miller, L.A., Vincent, W.F. & Deming, J.W. 2006. Archaea in particle-rich waters of the Beaufort Shelf and Franklin Bay, Canadian Arctic: Clues to an allochthonous origin? Limnology and Oceanography 51: 47-59.
