What Are Archaea?

Archaea are a group of microscopic organisms that were discovered in the early 1970s. Like bacteria, they are single-celled prokaryotes. Archaeans were originally thought to be bacteria until DNA analysis showed that they are different organisms.

There is still much about archaeans that is not known. What we do know is that many are extreme organisms that live and thrive under some of the most extreme conditions, such as extremely hot, acidic, or alkaline environments.

Archaeans have a typical prokaryotic cell anatomy: plasmid DNA, cell wall, cell membrane, cytoplasm, and ribosomes. Some archaeans also have long, whip-like protrusions called flagella, which aid in movement.

Organisms are now classified into three domains and six kingdoms. The domains include Eukaryota, Eubacteria, and Archaea. Under the archaea domain, there are three main divisions or phyla. They are: Crenarchaeota, Euryarchaeota, and Korarchaeota.

Crenarchaeota consist mostly of hyperthermophiles and thermoacidophiles. Hyperthermophilic microorganisms live in extremely hot or cold environments. Thermoacidophiles are microscopic organisms that live in extremely hot and acidic environments. You would find these organisms in hydrothermal vents and hot springs.

Examples of Crenarchaeotans include:

Sulfolobus acidocaldarius - found near volcanic environments in hot, acidic springs containing sulfur.

live in temperatures between 90 and 113 degrees Celsius.

Euryarchaeota organisms consist mostly of extreme halophiles and methanogens. 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, ice lakes, the guts of animals (cow, deer, humans), and in sewage.

Examples of Euryarchaeotans include:

Halobacterium - include several species of halophilic organisms that are found in salt lakes and high saline ocean environments.

Methanococcus jannaschii was the first genetically sequenced Archaean. This methanogen lives near hydrothermal vents.

these psychrophilic (cold-loving) methanogens were discovered in Antarctica and can survive extremely cold temperatures.

Korarchaeota organisms are thought to be very primitive life forms. Little is currently known about the major characteristics of these organisms. We do know that they are thermophilic and have been found in hot springs and obsidian pools.

Archaea are interesting organisms in that they have genes that are similar to both bacteria and eukaryotes. 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.

While Archaeans are very similar to bacteria, they are also much different. Unlike some types of bacteria, archaeans can not perform photosynthesis. Similarly, they cannot produce spores.

Archaeans are extremophiles. They can live in places where most other life forms cannot. They can be found in extremely high temperature environments as well as extremely low temperature environments.

Archaeans are a natural part of human microbiota. At present, pathogenic archaeans have not been identified. Scientists assume that they do not exist.