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What Are the Two Types of Archaea?

Originally called archaebacteria when discovered in the 1960s by Dr Carl Woese and his colleagues, the archaea resemble bacteria in size and appearance but are in fact an entirely different domain of life with a distinct DNA structure.. They are found all over the globe but are most known for being the only forms of life able to live in many of the world's most extreme environments. They are mainly divided into two broad groups -- crenarchaeota and euryarchaeota -- based on the types of environments they inhabit. Crenarchaeota are those archaea that live in extreme temperatures or acidity levels, and euryarchaeota are those that live in extremely salty waters or the intestines of animals. Each type has notable subcategories depending on their type of adaptation. A third "group," the korarchaeota, is comprised of archaea about which very little is known.

Thermophiles and Hyperthermophiles
- A subcategory of crenarchaeota, these archaea survive in extremely hot environments such as deep-sea heat vents and hot springs. Thermophilic archaea survive at more than 60 degrees Celsius (140 degrees Fahrenheit). Hyperthermophilic archaea push the limit even farther, living at above 80 degrees Celsius (176 degrees Fahrenheit). Both types survive through the use of rare heat-resistant enzymes that prevent their cellular structure from denaturing, as the cells of other organisms would.
Psychrophiles
- At the opposite end of the temperature spectrum, the psychrophilic archaea live in extremely cold environments, at least below 15 degrees Celsius (59 degrees Fahrenheit). Their cells have adapted to function even at slowed cellular activity and to deal with the threat of ice forming within the cell.
Acidophiles
- The third subcategory of crenarchaeota archaea live in extremely acidic environments between pH 1 and 3. Acidophilic archaea have evolved to have inverted cellular membranes coupled with other buffering abilities that allow them to withstand environments that would dissolve most other organisms.
Halophiles
- A subcategory of euryarchaeota, halophilic archaea live in water with extremely high salt content, even approaching the point of complete saturation. Most other organisms cannot survive such high salinity because the salt would draw too much water from their cells via osmosis. Halophilic archaea have adapted to be the only organism to use the salt-in process, whereby they employ specially designed enzymes and proteins that can function in the presence of high salt levels.
Methanogens
- Another subcategory of euryarchaeota, methanogens are found in the intestines of animals, including cattle, termites, aquatic life and even sometimes humans. They produce methane as a waste product, and, unlike some bacteria, they are not known to cause any diseases in their hosts.

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