Archaeans were originally thought to be bacteria until DNA analysis showed that they are different. In fact, they are so different that the discovery prompted scientists to come up with a new system for classifying life.
There is still much about archaeans that is not known. What we do know is that they can exist under some of the most extreme conditions, such as extremely hot, acidic, or alkaline environments.
There are three main divisions of archaeans. These divisions are: Crenarchaeota, Euryarchaeota, and Korarchaeota.
Hyperthermophilic microorganisms live in extremely hot or cold environments.
Thermoacidophiles are microscopic organisms that live in extremely hot and acidic environments. Their habitats have a pH between 5 and 1. You would find these organisms in hydrothermal vents and hot springs.
- Sulfolobus acidocaldarius - found near volcanic environments in hot, acidic springs containing sulfur.
- Pyrolobus fumarii - live in temperatures between 90 and 113 degrees Celsius.
Extreme halophilic organisms live in salty habitats. They need salty environments to survive. You would find these organisms in salt lakes or areas where sea water has evaporated.
Methanogens require oxygen free (anaerobic) conditions in order to survive. They produce methane gas as a byproduct of metabolism. You would find these organisms in environments such as swamps, wetlands, the guts of animals (cow, deer, humans), and in sewage.
- Halobacterium - include several species of halophilic organisms that are found in salt lakes and high saline ocean environments.
- Methanococcus - Methanococcus jannaschii was the first genetically sequenced Archaean. This methanogen lives near hydrothermal vents.
Phylogenetically speaking, archaea and bacteria are thought to have developed separately from a common ancestor.
Eukaryotes are believed to have branched off from archaeans millions of years later. This suggests that archaeans are more closely related to eukayotes than bacteria.