The Domain Archaea: Finding Life’s Extremists

Domain Archaea / Archaebacteria
The hot springs of Yellowstone National Park, USA, were the first places Archaeans and microbes were discovered.
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Domain Archaea/Archaebacteria: In the 1970s, while studying the relationships among prokaryotes using DNA sequences, a scientist named Carl Woese discovered some “unusual” organisms that appear to be very distinct from prokaryotes and eukaryotes.

Interestingly, these seemingly “unusual“ organisms were neither prokaryotes nor eukaryotes and the extreme difference at genetic and molecular level lead scientists to the discovery of the third domain of life – the Domain Archaea.

Members of the domain Archaea, or simply Archaeans, are extremely abundant in environments that are hostile to all other life forms; hence, their place among other living organisms long went unrecognized.

The domain Archaea is such a remarkably diverse and successful clade of organisms. Let’s take a closer look and find out why:

History of the Domain Archaea

Prior to its separation, the domain Archaea was formerly called the domain “Archaebacteria“, which is actually a misnomer since these organisms were not bacteria but belong to a separate clade.

  • The name “Archaebacteria” was previously an untested hypothesis about the evolutionary status of the organisms having a type of metabolic ability that seems to be highly suited to the primordial conditions of life on Earth.
  • Therefore, there is a large possibility that this novel group of organisms is actually the oldest.

The three domains of life are illustrated below; showing each of the domains is very distinct from the others. Check out the domain eukarya in detail here.

3 Domains

Characteristics of Archaea

Extremophiles
Source: Flickr
While Archaeans truly look and appear like most bacteria, they are biochemically and genetically distinct from them. In fact, scientific studies reveal that they are even closer to their eukaryotic counterparts rather than the prokaryotic ones.

  • One of the most distinguishing traits of these organisms is their ability to inhabit some of the most extreme environments (hence, they are sometimes referred to as “extremophiles“). Some of them thrive in hydrothermal vents in the deep ocean at temperatures of over 100 degrees Celsius high.
  • Some of them live in either extremely acidic or basic waters while some are found to inhabit the digestive tracts of animals. While some of them even live in petroleum deposits underground.
  • In terms of reproduction, Archaeans undergo asexual reproduction through binary fission, Meaning, the genetic material (DNA) simply duplicates as the cell wall pinches off the cell.

Intermediate Characteristics of Archaebacteria

The members of the domain Archaebacteria possess a curious mix of the characteristics of prokaryotic and eukaryotic organisms. The table below showcases some of those intermediate traits.

PROKARYOTIC TRAITS EUKARYOTIC TRAITS
Circular chromosome DNA contains histones and other nucleosome-like structures
Has operons but lack introns Mechanism for DNA replication, transcription, and translation
Able to perform metabolic functions like energy generation, synthesis of polysaccharides, and nitrogen fixation Has the RNA polymerase for transcription, and initiation and elongation factors for translation

But on top of all of these, Archaeans have some genes that aren’t like any found in anything else.

For instance, Archaeans that thrive in extremely saline environments have special defensive molecules and mechanism from breaking the cells out.

Another thing is that some Archaeans have molecules that come in contact with acids in order to help them prevent from bursting.

The Three Types of Archaebacteria

The domain Archaea is a group of unusual organisms and is known to include three groups: methanogens, extreme halophiles, and thermoacidophiles.

1. Methanogens

Methane Producing Archaea From Cow's Burps
Methane Producing Archaea From Cow’s Burps
As their name suggests, methanogens are Archaeans that are capable of producing methane (gas), and this amazing ability of producing methane makes them easily distinguishable in the digestive tract (intestines).

  • Basically, these organisms are found in environments that have no oxygen (anoxic) : in muddy marshes and swamps, and in the digestive tracts of cows, termites, and marine life.
  • Methanogens get their energy from their utilization of hydrogen and carbon dioxide.
  • At present, two methanogens have already had their complete sequenced genome: Methanocaldococcus jannaschii and Methanothermobacter thermoautotrophicus.

The chemical equation for methane gas is:

4H2 + CO2 => CH4 (Marsh Gas) + 2H2O

2. Extreme Halophiles

Great Salt Lake in Utah
Great Salt Lake in Utah
Halophiles (coming from the Greek word “hals” which means “sea” or “salt“), are a type of Archaea that inhabit extremely salty environments like the Dead Sea or the Great Salt Lake in Utah.

  • Interestingly, these extreme halophiles produce the pigment bacteriorhodopsin that gives them the ability to utilize sunlight as the source of energy, in the same manner that plants use it for photosynthesis.
  • Aside from the sea, halophiles can also live in the soil as long as the salt level is very high.

3. Thermoacidophiles

Sully Vent (Black Smokers)
Sully Vent (aka Black Smokers) in Northeastern Pacific Ocean.
Thermoacidophiles, as their name suggests, are Archaea that thrive in both hot and acidic environments, especially in those in near sulfur hot springs.

  • The ideal temperature and pH levels for thermoacidophiles is at 70 degrees Celsius (and higher) and at pH levels of 1 or 2 (similar pH as concentrated sulfuric acid.
  • However, when subjected to lower temperatures below 55 degrees Celsius (131 degrees Fahrenheit), they die.

Despite this, it is important to note that not all Archaea are extremophiles. In fact, many of them thrive in normal environmental conditions. In particular, some of them can be found alongside with bacteria and some marine plants in the ocean.

Importance of Archaea (Commercial Uses)

Archaeans in Detergents
Archaeans in Detergents
Because of their tolerance to high temperatures and relatively extreme environments, some members of the domain have already been exploited for a wide variety of commercial uses.

  • These Archaea become the source of enzymes that are usually added to detergents in order to help it maintain its activity even at higher temperature and pH.
  • Some enzymes from Archaea are also used to convert cornstarch into the fiber dextrin.
  • Some Archaea also bear the potential for bioremediation or help in cleaning contaminated sites.
  • The thermophilic Archaea, Thermus aquaticus, is a very essential part of the development of molecular biology as a science. This is because this Archean has become the source of the enzyme harnessed as the basis for the amplification of the DNA in a technique called Polymerase Chain Reaction (PCR).

At present, members of the domain Archaea may be the only organisms that can survive in extreme habitats. Much is still to be discovered about these microorganisms, and as the advancement of technology becomes more extensive, the understanding of the microscopic world becomes more comprehensive as well. In the near future, we might as well be introduced to new domains of life that were previously unknown to science or creatures that weren’t imagined to even exist. Who knows?

Cite this article as: "The Domain Archaea: Finding Life’s Extremists," in Bio Explorer, March 15, 2017, https://www.bioexplorer.net/domain-archaea-archaebacteria.html/.

References

  • “Archaebacteria: The Third Domain of Life Missed by Biologists for Decades – Scientific American”. Accessed March 13, 2017. Link.
  • “Archaebacteria – Groups Of Archaebacteria – Genetic, Organelle, Cell, and Called – JRank Articles”. Accessed March 13, 2017. Link.

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