-Sebastian Sylvestre

external image Halobacteria.jpg
"Halobacteria" (also known more correctly as "Haloarchaea") [2]

The domain archaea is believed to the closest relative of the domain eukarya because the small-subunit ribosomal RNA (SSU-rRNA) of the archaea kingdom is more similar to the SSU-rRNA of the eukarya domain than that of the bacteria domain.[1]

Diagnostic Characteristics:

Archaea is a group of single-celled microorganisms. The organisms are singularly referred to as archeaons. Archaea are prokaryotes, and were originally thought to be a subgroup of Bacteria and were originally referred to as Archaebacteria. However, under the three-domain system recently proposed, Archaea are now classified under their own domain due to their evolutionary history. (7 Nangia)
Species within the domain archaea are recognized predominantly for there ability to live where no other organisms can. They are most commonly referred to as the extremophiles, which literally translates to "lovers" of extreme environments. They include some of the strictest anaerobes, meaning they do not require oxygen to survive and may even be harmed when in the presence of oxygen. The dense growth of some of these organisms, particularly the "extreme halophiles," literally meaning extreme "salt lover," can result in vivid purple-red colorations due to a photosynthetic pigment called bacteriorhodopsin, as can be seen in the seawater evaporating ponds at the edge of San Francisco Bay, which has a salinity (salt concentration) that can reach up to 15-20%. This photosynthetic pigment is rather similar to rhodopsin, the pigment found in vertebrate retinae [5] (OZ). There are some species that actually require such harsh environments to even survive, perhaps requiring an environment that is ten time saltier than seawater. Many also have flagella, that are attached to the membrane by basal apparatus which acts as a motor that rotates the flagella to direct the archaea and power its movement. Unlike eukaryotic flagella, archaea flagella are not covered by an extension of the plasma membrane. (SV) [1]
Although Archaea look much like bacteria, they are quite different. Their cell walls contain different amino acids and sugars than in bacteria cell walls. In addition, the cell membranes of Archaea are different than bacterial membranes. (12)(RJS)
A photograph of Archaea (KN) (9)
A photograph of Archaea (KN) (9)

Many archaea are "extremophiles," meaning they are organisms that thrive in and may even require physically or geochemically extreme conditions, such as hot springs and volcanoes, arctic regions, or regions that have either extremely high or extremely low pH levels; conditions that are otherwise detrimental to the vast majority of life on Earth, thus establishing an ecological niche for the archaeal organisms. In fact, they are the only organisms that have the ability to grow at temperatures above 100
Some archaea, Crenarchaeota, have recently been noted to be widedly distributed in low-temperature environments like ocean waters and land sediment and soil (ER) [3].

Major Types:
The two major types of archaea are Crenarchaeota, which includes the majority of the thermophiles, and Euryarchaeota, which includes all the methanogens, halophiles, and some of the thermophiles and psychrophiles; both of which include some species of recently discovered marine archaea.[1] Methanogens release methane gas as a waste product during their digestive processes (SES 13). Halophiles generally live in salty environments (SES 13). Thermophiles live in extreme hot habitats, while psychrophiles inhabit extremely cold environments (SES 13).

Most species of Crenarchaeota have flagella and are motile (are able to move). Most species are anaerobic, but a few are aerobic. Most species oxidize (take an electron from) sulfur and hydrogen or reduce (add an electron to) sulfur and nitrates (forms of nitrogen) in order to meet their energy needs. Some other species use organic substances for their energy needs [3] (DP).

Species of Euryarchaeota live in extremely salty environments, such as salt lakesor on the surfaces of highly salted foods like fish and meats(7 VM). They specialize in living in extremely hot environments as well, such as hydrothermal vents on the sea bed and in hot springs(7 VM). Many euryarchaeota lack a cell wall (but do have a cell membrane as they are still cells) (7 VM).

Some sources have outlined another major type of archaea called the Korarchaeota (8,DJ). Species of Korarchaeota are differentiable from the others by a 16S rRNA gene sequence, but no organisms have been collected or cultured, only nucleic acids (8, DJ). The Korarchaeota species could be the least evolved species ever discovered in life (8, DJ).
Basic Anatomy:
Unlike eukarya, archaea possess no nuclear envelope, nor any membrane enclosed organelles; and unlike bacteria, archaea possess no peptidoglycan in their cell walls. Archaea have some branched hydrocarbons as membrane lipids, and they also have several kinds of RNA polymerase. Some of the key similarities among archaea and eukarya include methionine as the initiator amino acid for the start of protein synthesis, histones that are associated with DNA, and the ability to continue to grow in the presence of antibiotics, such as streptomycin and chloramphenicol. Unlike eukarya cells, however, the chromosomes present in archaea cells are circular. Lastly, introns, or noncoding parts of genes, are present in only some of the genes of archaea. [1]
Basic Anatomy (10, NK)

Basic Archaeal Structure : The three primary regions of an archaeal cell are the cytoplasm, cell membrane, and cell wall. Above, these three regions are labelled, with an enlargement at right of the cell membrane structure. Archaeal cell membranes are chemically different from all other living things, including a "backwards" glycerol molecule and isoprene derivatives in place of fatty acids.
(HS 4)

Transport of Materials:
Because archaea are prokaryotic cells, they, like bacteria, lack interior membranes, so their cells do not contain organelles that can aid in the transport of materials. As a result much of the transport that does occur is passive, meaning that they rely on their surroundings to provide the nutrients they need as their membranes will incorporate the material, either with the aid of proteins or by simply engulfing the material through endocytosis. Endocytosis is when the cell wall opens up to for a mouth. Then the cell wall closes around the foreign material and then it pushes the food into the cell.(SJB)(1). They also resemble bacteria in that their cell membrane is usually bounded by a cell wall. Because of this great dependence on the surroundings for nutrition, archaea tend to form colonies, in which it becomes easier to digest materials and transport the materials among neighboring cells. [1]

Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding. Stages of growth and reproduction of archaea have similarities with both that of eukarya and bacteria. The cell division in archaea is controlled in a cell cycle in which after the cell's plasmid, or small circular chromosome that consists only a few genes, is replicated, the two daughter plasmids are separated and the cell divides. Archaea can also undergo transformation, in which the cell take up genetic information from its surroundings, leading to genetic variation, conjugation, in which two cells directly transfers parts of their genes to each other, also leading to genetic variation, and transduction, in which viruses transfer genes among the prokaryotic cells. A notable difference between the domain archaea and the other two domains, bacteria and eukarya, is that spores are made by both bacteria and eukaryotes, but are not formed in any of the known archaea.[1][2]

27-x1-ProkaryoteConjugation.jpg<http://images.google.com/imgres?imgurl=http://io.uwinnipeg.ca/~simmons/16cm05/1116/27-x1-ProkaryoteConjugation.jpg&imgrefurl=http:>It is hard to tell, but this is a photo of an two archaea conjugating ( a form of reproduction). During this process, as said above, the two cells will directly transfer parts of their genes to each other. This (conjugation) is as close as archaea will get to sexual reproduction. (Jesse Carmen) When these archaea are attached like this, they exchange DNA in the form of plasmids, which are small rings of DNA. The plasmids in the bottom archaea may encode for the spines we see, so maybe the upper archaea will start to grow spines as well since they are exchanging DNA (BL).

Environmental Adaptations:
Others of the extremophiles include extreme thermophiles and methanogens. "Extreme thermophiles" literally means extreme "heat lover," and they thrive in very hot environments; the optimal temperature conditions for this type of archaea ranges from 60-80º. These organisms live in deep-sea vents and other extremely hot environments. One source says that the ability for these extreme thermophiles to be able to survive in this extremely hot areas is due to the presence of heat stable proteins. These heat stable proteins are densely packed so they exclude internal water, and they also more hydrophobic than regular proteins you would see in archaea ( 6,GR) It is believed by some scientists that the earliest forms of life were extreme thermophiles that inhabited environments that were similar to deep-sea vents. The methanogens are actually poisoned by oxygen; they require CO2 to obtain energy by oxidizing H2, releasing methane, CH4, as a waste product. They require environments in which all the oxygen has been depleted and used up by other microbes, such as in swamps and marshes; these archaea play an important role in decomposition and are also found within the guts of animals, aiding in the digestion of certain materials; for example, they are present in the gut of cattle, termites, and other herbivores that live mostly on a cellulose diet. [1] Another type of extremophile includes psychrophiles, which thrive in cold environments. There are also halophiles, which inhabit very saline environments (like the Dead Sea). There are also acidophiles who live in pHs (acidity level) as low as 1 and die at pH 7. Conversely, there are alkaphiles which thrive at high pHs. (11)(AR).

Review Questions:
1. List and differentiate between the two major types of Archaea. (YS)
2. What differentiates archaea from bacteria that would place them in seperate domains? (RK)
3. How do Archaea reproduce? (KN)
4. How do archaea adapt to extreme environments? (JAC)
5. Why does it help archae survive better by forming colonies? (HZ)
6. Explain how archaea transport materials without organelles. (BMB)

[1] Campbell, Neil A., and Jane B. Reece. Biology. Boston: Benjamin-Cummings Company, 2001. 531-532, 535-37.
[2] "Archaea" Wikipedia <http://en.wikipedia.org/wiki/Archaea>
[3] Barns, Sue and Siegfried Burggraf. 1997. Crenarchaeota. Version 01 January 1997. http://tolweb.org/Crenarchaeota/9/1997.01.01 in The Tree of Life Web Project, http://tolweb.org/
(4) Waggoner, Ben. "Archaea: Morphology." Introduction to Archaea. 2001. University of California Museun of Paleontology. 3 Dec. 2008 <http://www.ucmp.berkeley.edu/archaea/archaeamm.html>.
"Introduction to the Archaea." 25 Nov. 1994. UC Berkeley. 7 Dec. 2008 <http://www.ucmp.berkeley.edu/archaea/archaea.html>.
[6] Darling, David. "The Encyclopedia of Science: Extremophiles Microbiology." 7 Dec. 2008 <http:// www.daviddarling.info/images/thermophiles.jpg>.
[7] "Euryarchaeota."7 Dec. 2008 <http://www.earthlife.net/prokaryotes/euryarchaeota.html>
[8] Todar, Kenneth. "IMPORTANT GROUPS OF PROCARYOTES." Todar's Online Textbook of Bacteriology. 2008. University of Wisconsin. 8 Dec. 2008 <http://www.textbookofbacteriology.net/procaryotes.html>.
University of South California. <http://pathmicro.med.sc.edu/fox/e_coli-dk.jpg>.
10) http://www.bio.miami.edu/dana/pix/prokaryote.jpg
11)"Archaea." 14 Dec 2008. <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Archaea.html>.
12."Archaea and Other Extremists." 18 Dec 2008 <http://www.microbeworld.org/microbes/archaea/>.

13. "Types of Archaea." Archaea and Other Extremists. 18 Dec. 2008. <http://www.microbeworld.org/microbes/archaea/>

Page Edited by: DP; Hilary Stepansky, Sarah Vlach, Omer Zaidi, Ethan Richman, Grace Rehnquist, Vonai Moyo, Daisy Joo, Kevin Nayer, Jesse Carmen, Rachel Kornetsky, Josh Czik, Becca Levenson, Sam Blatchford, Hanna Zhu, Sarah Schwarzschild, Brittany Marcus-Blank