Adaptive Archaea

Discovered in 1970, Archaea might be the least well-known of the three domains of life (the others being Bacteria and Eukaryota), but it is a fascinating and diverse group of organisms and quite possibly the first on Earth. Like bacteria, archaea are unicellular, prokaryotic organisms, meaning that they lack nuclei and other membrane-bound organelles in their cells. However, archaea are more closely related to eukaryotes (including us!), than to bacteria. According to the Theory of Endosymbiosis, the line of descent from the Last Universal Common Ancestor first split into Bacteria and Archaea.

The Tree of Life showing that Archaea and Eukaryota are more closely related to each other than to bacteria.
Image credit: John D. Croft via Wikimedia Commons

Archaea are particularly interesting to astronomers because this domain contains a large portion of extremophiles, organisms that can thrive in extreme conditions. Some of the first archaea were discovered in the hot springs of Yellowstone National Park. Others have been discovered within the digestive tracts of various organisms, in underground petroleum deposits, or in waters with extreme pH (in either direction). It is notable that archaea developed in the much harsher conditions of the early Earth, which lacked “features” such as the ozone layer to keep out ultraviolet radiation.

One of the most interesting and best-studied groups of archaea is the Halobacterium (a bit of a misnomer, as it is not a bacterium at all!), which thrives in extremely salty water. This property opens up the possibility that they might survive on Mars, where liquid salt reservoirs have been discovered just last year. Experiments have already demonstrated that two types of halobacterium (Halococcus dombrowskii and Halobacterium sp. NRC-1) can survive conditions similar to those on Mars, including an atmosphere made almost completely (98%) of carbon dioxide, and an average temperature of -60˚C. In addition, Halobacterium salinarum NRC-1 can survive environments of high radiation because it has an unusual adaptation: multiple copies of its genes, spread out across different chromosomes. This way, if radiation damages one gene copy (or even two), the cell survives off the remaining copy(s), while it repairs the damage. Thus, the Halobacterium are a wonderful model for the types of organisms that might be found on Mars if we continue to explore! 

Sources:

“Archaea – The Most Ancient Life.” The Virtual Fossil Museum. Web.

Fox-Skelly, Jasmin. “Earth – The Microbes so Extreme They Might Survive on Mars.” BBC, 21 Dec. 2015. Web.

Hallsworth, John E. “What on Earth Could Live in a Salt Water Lake on Mars? An Expert Explains.” Phys.org, 6 Sept. 2018. Web

“Introduction to the Archaea.” UC Museum of Paleontology, University of California, Berkeley. Web.

Rampelotto, Pabulo Henrique. “Extremophiles and Extreme Environments.” Life (Basel), 7 Aug. 2013. Web.

4 thoughts on “Adaptive Archaea

  1. It is interesting how you noted that archaea developed in the early Earth, where conditions would have been much harsher than they are today. Perhaps that is why so many of the extremophiles that have been discovered are archaea, because they were forced to adapt to those extreme conditions and many of their adaptations persist in today’s extremophiles.

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  2. I like how you introduced your paragraph about extremophiles with a description of the phylogenetic tree, I think that made your discussion about extremophiles much more understandable- good job! Also, I found it interesting that halobacterium have an innate defense mechanism against radiation, which is why halobacterium would be similar to the types of organisms that we would find if there is indeed life on Mars.

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  3. You’re definitely right in saying we don’t know much about archaea–this blog caught me up on a lot that I didn’t know about, so thank you! What I’m interested in is why archaea more closely related to eukaryotes than bacteria, if they’re prokaryotes? I’m also curious why so many of them thrive in conditions that we consider to be extreme. Is it that they’re prokaryotes? If so, what makes archaea more special than other types of prokaryotes?

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