Diagnostic Characteristics

Archaea are one of the two prokaryotic domains and are easily distinguishable from other organisms as they thrive in extreme environments, with some species capable of weathering 100°C. Being prokaryotes, they contain no membrane bound organelles, no nuclear envelope, and a circular chromosome. Some archaea characteristics that differ from prokaryotes are their lack of peptidoglycan in cell walls, and containing some branched hydrocarbon membrane lipids, as well as having more than one kind of RNA polymerase. Archaea also use methionine as an amino acid initiator in protein synthesis and are not inhibited by antibiotics streptomycin and chloramphenicol.

There are also certain characteristics of the Archean RNA that differs from the bacterial RNA. Primarily, the Archean RNA is more complicated than the bacterial RNA in that it contains typically 8 to 10 proteins embedded, as opposed to the typical 5 in a bacteria. Also, the RNA polymerase (an enzyme) in the Archean RNA is not affected by the antibiotic rifampicin, which is a known inhibitor of the bacterial RNA. (RK)

The domain Archaea is relatively new, discovered by a team of scientists studying prokaryotic relationships at the University of Illinois in the late 1970s when they realized prokaryotes consisted of two distinct groups: archaea and bacteria. Dr. Carl Woese is generally credited with this breakthrough. These novel findings led to the supremacy of the current three-domain system. (MR; Source 11)

Multicolored thermophilic archaea around the Grand Prismatic Spring
Multicolored thermophilic archaea around the Grand Prismatic Spring


Archaea are a distinct, unique and interesting domain of prokaryotes. They are special in that they are typically found in extreme environments. These range from places with extremely high temperatures, like hot sulfur springs and deep-sea hydrothermal vents, to highly saline places, like the Dead Sea. These organisms are known as extremophiles,a name that aptly describes their penchant for intense locales.
They can survive inside the digestive tracts of cows, termites, and marine life where they produce methane(MP).
Extremophile archaea are divided into four main groups: halophiles, thermophiles, alkaliphiles, and acidophiles. Halophiles live in very saline environments, thermophiles live in very warm areas, and alkaliphiles and acidophiles live in very alkaline or acidic environments. (CM)

Archaea also inhabit another type of extreme environment: the Antarctic. They are one of a few select organisms that have been found in the Antarctic’s incredibly cold waters. These types of cold-loving archaea are called psychrophiles. However, not all archaea live in such extreme environments; in fact, archaea have been discovered in “rice paddies, soils, swamps, freshwater, and throughout the oceans.” (MR; Source 10)

A deep-sea hydrothermic vent, or home, to a thermophilic flavor of archaea
A deep-sea hydrothermic vent, or home, to a thermophilic flavor of archaea
Hot Spring's where archaea thrive (PS

Major Types

A close up of a Euryarchaeota (MM)

Archaea are divided into two major taxa, Euryarchaeota and Crenarchaeota. Euryarchaeota are comprised of the methanogens and extreme halophiles, whereas Crenarchaeota are primarily extreme thermophiles. Methanogens obtain energy by using CO2 to oxidize H2 , producing methane waste. Oxygen serves as a poison to methanoegns, and as such, they live in swamps and marshes where other microbes have consumed the oxygen. Extreme halophiles, on the other hand, live in areas of extreme salinity, such as the Great Salt Lake and the Dead Sea. Halophiles form colonies of purple/red scum in these locales. Thermophiles are found in hot environments around the world, ranging from hot sulfur springs to deep-sea hydrothermal vents. Optimal conditions for this variety of archaea range from 60-80°C, yet some deep-sea vents are closer to 105°C.

Methanogens are obligate anaerobes, meaning they cannot grow in the presence of oxygen. Thus, methanogens are found in habitats such as marine and freshwater sediments, intestinal tracts of animals, and even sewage treatment facilities. (TB)

Metabolically, Crenarchaeota are quite diverse, ranging from chemoorganotrophs to chemolithoautotrophs. They are anaerobes, facultative anaerobes or aerobes, and many utilize sulfur in some way for energy metabolism. Several species are primary producers of organic matter, using carbon dioxide as sole carbon source, and gaining energy by the oxidation of inorganic substances like sulfur and hydrogen, and reduction of sulfur or nitrate. Others grow on organic substrates by aerobic or anaerobic respiration or by fermentation. (RW)

Basic Anatomy

Seeing as archaea are one of the two domains of prokarya, their anatomy is more or less consistent with other prokarya, like bacteria. Prokarya come in three shapes: spheres (cocci), rods (bacilli), and helices (spirilla and spirochetes).A distinct feature among these is a cell wall that maintains the shape of the cell, provides protection from the environment and prevents the cell from bursting in a hypotonic environment. Along the surface of the cell, archaea have flagella, which allow it to move. These flagella can be concentrated at either end of the cell, or scattered along the surface. The diamter of a prokaryote cell is in the range of 1-5 mm (compared to 10-100 mm of eukaryotic cells). Internally, the DNA is concentrated in the form of a snarled fiber, essentially a ring, in a nucleoid region. Prokaryotes can also have more small rings of DNA called plasmids, but they consist of fewer genes.

Basic thermophilic coccus archaea with flagella concentrated on one end.
Basic thermophilic coccus archaea with flagella concentrated on one end.
A methanogenic archaea
A methanogenic archaea
A halophilic Halobacterium salinarium
A halophilic Halobacterium salinarium

Transport of Materials

Archaea make use of passive and active transport to take in materials from the environment. Passive transport requires no energy, and is a result of diffusion across a concentration gradient. In this way, nutrients move from areas of higher to lower concentrations, thus transporting into or out of the cell through the selectively permeable phospholipid membrane. Archaea can also transport materials with the help of transport proteins by way of facilitated diffusion. Active transport becomes important when going against the concentration barrier. This requires ATP, and is performed by proteins embedded in the membrane, like the sodium-potassium pump.
When it comes to larger molecules, the cell uses different techniques. When secreting large molecules, exocytosis is used, which fuses vesicles with the membrane. In endocytosis, the cell intakes large molecules by forming new vesicles from the membrane. There are three different types of endocytosis- phagocytosis, where a cell engulfs a particle, pinocytosis, which is when the cell takes in droplets of fluid which dissolve substances, and receptor mediated endocytosis which is when proteins with specific receptor cites are exposed to extracellular fluids, and ligands bind to them.

Phagocytosis. A material, called the phagosome, enters the cell. (Matt B - Source 4)


Being prokaryotes, archaea abide by the general reproductive characteristics of the group. They reproduce only asexually, and only using a type of cell division known as binary fission, which is essentially synthesizing DNA close to constantly. Prokaryotes, however, also have three mechanisms for gene transfer. Transformation is the process by which the cell takes genes from its environment, which will allow for genetic transfer between prokaryotes. Conjugation is when genes are directly transferred between prokaryotes, and in Transduction, viruses are the middlemen that transfer genes among prokaryotes.

In binary fission, the cell divides in two parts, each with the potential to grow into an adult archea. Unlike mitosis, binary fission does not utilize spindles. Instead, each set of DNA attaches to one side of the cell membrane and is pulled apart when the cell separates. The membrane elongates until the cell is doubled in size length, then the membrane pinches together to create two cells. (LPE)

Binary fission- the method of reproduction for archaea
Binary fission- the method of reproduction for archaea

Conjugation in Archaea (IL- 9)

Environmental Adaptations

Archaea have evolved several methods of withstanding the harsh conditions they are known to be found in. Methanogens obtain energy by using CO2 to oxidize H2 in environments that contain no oxygen. Some thermophiles obtain energy by oxidizing sulfur. There is research, however, that postulates that the earliest prokaryotes evolved were thermophiles that lived in environments most similar to deep-sea vents, which would mean that other organisms are ‘cold-adapted’ rather than archaea being ‘extreme’. This would mean that archaea are the original template, and other organisms are adapted from them.
Taxis movement is another environmental adaptation where it moves towards or away from a certain stimulus. This can help keep Archaea away from toxins and near food or oxygen. They also have a protective layer called a capsule so that they can stick to the surfaces that they secrete (jets of slime). The capsule also helps them be resistant to pathogenic prokaryotes. (AP)

Review Questions
1) Where are the divisions in archea? what are the two group and the main differences between the groups? (RJ)
2) What is facilitated diffusion and how do archaea use it to transport materials? (CP)
3) Explain binary fission. How is this process similar and different from mitosis? (AR)
4) Explain some of the environmental adaptations archaea have made? (VN)
5) What are the three types of endocytosis and what is the function of each type? (ZJ)
6) What are thermophiles and what are some ways in which they obtain and maintain energy? Give an example. (MB)
7)What is the difference between transformation and transduction? (MP)
8) Although they have inherently similar anatomies, how do archea and bacteria differ? (JS)
9) What are the characteristics that differentiates Archeans from bacteria? Why are the two group of Archeans not considered different kingdoms, yet bacteria are? (MS)

1. Campbell, Neil A., and Jane B. Reece. Biology. Boston, MA: Pearson Custom/Benjamin Cummings, 2002. Print.
2. (TB)
3. LPE

4 (Matt B)
5 (MM)
6. "Kingdom Archaea." Home Page for Ross Koning. Web. 11 Nov. 2011. <>. (AP)
7. (RK)
8. (RW)
9. (IL)
10. "Archaea." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2008. Gale Science In Context. Web. 30 Nov. 2011.
11. Waggoner, Ben, and Brian Speer. Introduction to the Archaea. U of California, 2006. Web. 30 Nov. 2011. <>.