Halophile Archaea
By: Evan Kates


A picture of halophile archaea.
A picture of halophile archaea.

external image bactcell.jpg
Image displays the various structures and pars of a bacteria cell.

1.) Classification/Diagnostic Characteristics
Halophiles are in the domain Archaea. This domain is recently named and separated from its previous overarching domain that included bacteria. The Archaea's differences in sequence of the ribosomal RNA and many other differences led to this split in the phylogenetic tree. The Archaea are prokaryotic cells, not sensitive to many antibiotics, have no peptidoglycan, a marcromolecule, in their cell walls, and have unique membrane structures.

Archaea is able to survive in extreme environments. In a more broad spectrum, archaea are well known for surviving and prospering in extreme habitats such as highly concentrated areas of salt, areas of high or low temperatures, high or low pH values and low oxygen concentration areas. Also, a lot of archaea live deep in the depths of oceans. All archaea share some similar characteristics such as the absence of peptidoglycan in their [[#|cell walls]] and another similar characteristic is the presence of lipids of distinctive composition in their membranes. Halophile arhaea live in the dead sea and other lakes with pH values all the way u to 11.5. These archaea also contain a very vibrant red color.

2.) Relationship to Humans
Halophiles are found all over the world in hypersaline environments, many in deep sea locations and in artificial salterns used to mine salts from the sea. Thus humans can use Halophiles to gather precious minerals such as salt in places like the Dead Sea. (Cam Somers) Studies have shown that halophile archaea can survive in the human digestive tract even though it is not an overly salty environment. Further investigation of the existence of halophile archaea in the human digestive tract may lead to a better understanding of gastrointestinal health (Jillian Bunis).

3.) Habitat and Niche
Some halophile archaea have a very strange but efficient system for getting light energy and using it in the form of ATP. They don't use any chlorophyll even when oxygen is lacking. The trick they use the pigment "retinal' combined with a protein that forms a light absorbing molecule, "microbial rhodopsin". Halophile archaea live in the most extreme conditions and some live in the dead sea which is one of the saltiest bodies of water in the world. Most organisms would dry out and die but these archaea have adapted to living in these unique conditions.

Like all Halophiles, Halophile Archaea requires salt to be able to grow and thus are salt loving organims. It is very common for Halophiles to be classified on the amount of salt that they require to grow. This adaptation was very helpful because closer to the beginning of time, the water baths had a very high salt concentration.

Colonies of halophile bacteria deposits (the pinkish mounds) at a lake in Bitter Lake National Wildlife Refuge, Mexico (Prashant)
external image dr-diatoms2_html_2fb361e4.jpg

4.) Predator Avoidance
The location and geographic barriers of the living conditions for the halophile archaea make it extremely difficult, basically impossible, for any predators to survive in these conditions to even attack them. The archaea do not have any specific defense mechanisms except for their strange ability to live and survive in extreme conditions that other organisms cannot survive in, making it very difficult to prey on these halophile archaea.

5.) Nutrient Acquisition
Halophile archaea injust several nutrients such as salt, hydrogen gas, oxygen gas, sulfer and carbon dioxide. The archaea uses these nutrients for other functions such as energy. The archaea has a tough time acquiring nutrients because there are very few nutrients that can survive in the extreme conditions. These few nutrients that can survive in the very salty conditions, for example, are injested by the archaea and then used to support energy and sulfer.

Halophiles often use the [[#|citric acid]] cycle and an electron transport system (ETS) to metabolize foods. The citric acid cycle generates energy through the breakdown of acetate from carbohydrates, fats, and proteins into carbon dioxide. The electron transport system produces ATP, the "currency" of energy, by taking advantage of an electron donor like NADH and an electron acceptor like diatomic oxygen. (4) [GW]

6.) Reproduction and Life Cycle
Archaea reproduce asexually by binary fission, multiple fission, fragmentation, or budding. Meiosis does not occur, so if a species exists in more than one form, all of them have the same genetic material.
(Krieg, Noel (2005). Bergey's Manual of Systematic Bacteriology. US: Springer. pp. 21–6.)
However, as with all bacteria, it is possible for there to be a mutation in the DNA of a halophile.
Example of an archaea reproducing by budding
Example of an archaea reproducing by budding

7.) Growth and Development
Halophile archaea grew and adapted to their environment by developing a unique system used to convert light to ATP by using the retinal pigment which in turn combines with a protein to give the archaea a source of light-absorbing molecule called microbial rhodopsin. Here, we see that the halophile archaea developing to their environment and growing.

8.) Integument
The halophile archaea contain carotenoid pigments that give off a red color that can be seen in highly saline concentrated environments such as commercial seawater evaporating ponds. The pigments in the archaea such as the carotenoid change with the environment and vary colors depending on the concentration of the water. The colors range from a light pinkinsh color to a dark red color.
All archaea have protective cell walls that give the organism structure and mediate osmotic pressure changes and material exchanges with the environment. These cell walls are generally constructed from proteins such as pseudopeptidoglycan, polysaccharides, and glycoproteins. (4) [GW}

9.) Movement
The halophile archaea tends to be developed and formed in salty conditions such as the dead sea and in brines of all other types. They live in the driest, saltiest, coldest, hottest, and any other extreme type of condition. They spread quickly and can turn an entire sea a redish color. For example, in the San Francisco Bay, the archaea turns the water a dark reddish color because it is highly saline concentrated and that color change is the carotenoid pigments reacting to the saline.
Archaea often have flagella similar to bacteria. These flagella are often found in groups on the cells surface. (http://plantphys.info/organismal/lechtml/archaea.shtml)

10.) Sensing the Environment
Halophile archaea sense the environment they are in, which is usually a highly concentrated pH area, highly salted area, or highly saline concentrated area, by opting to take in the nutrients surrounding and extrovert those nutrients to energy. The archaea change color depending on the type of waters that they are in. For example, in the San Francisco Bay, the archaea turns the water a dark reddish color because it is highly saline concentrated and that color change is the carotenoid pigments reacting to the saline.

11.) Gas Exchange
Halophiles descended from methanogens, where they most likely acquired the genes for aerobic respiration. This means that the bacteria absorbs oxygen to react with glucose, generating ATP, and producing CO2 and water as waste products.
However, these bacteria can exist in both aerobic and anaerobic conditions.

12.) Waste Removal
Because archaea resemble bacteria, they dispel wastes through their cell membranes. Specific to archaea, they grow by oxidizing sulfur compounds and producing sulfuric acid as a waste product.
http://onlinelibrary.wiley.com/doi/10.1016/S0168-6496(03)00028-X/abstract;jsessionid=9CDFDFFDE3986A26A8403BF27FE72DB6.d02t01?systemMessage=Wiley+Online+Library+will+be+disrupted+on+15+December+from+10%3A00-13%3A00+GMT+%2805%3A00-08%3A00+EST%29+for+essential+maintenance (BHu)

13.) Environmental Physiology
Like mentioned previously, this specific archaea lives most efficiently in extreme conditions. These extreme conditions can consist of either very high/low tempereatures, extremely salty waters (ie. dead sea), and highly saline concentrated areas. The halophile archaea adapts and lives best in these types of extreme conditions and can be very easy to visibly see because they contain pink colored carotenoid pigments and tend to grow in the dead sea in the extreme salty conditions.

Whereas most non-halophilic organisms can only tolerate salt, or NaCl, concentrations of up to 0.2 moles per liter, halophiles thrive at NaCl levels of around 3.5 moles per liter. In order to prevent the loss of cellular water to the environment by osmosis, halophiles accumulate solutes within the cytoplasm, achieving internal solute concentrations greater than or equal to concentrations outside of the cell. Through the use of a sodium (Na+) pump, halophilic archaea are able to push sodium ions out of the cell, while concentrating potassium (K+) ions within the cell, thus balancing osmotic pressure. The balance of osmotic pressure generally consists of an internal concentration of potassium ions at 5 moles per liter and an outside concentration of sodium ions at 4 moles per liter. In addition to surviving environments with high salt concentrations, halophiles that inhabit hypersaline lakes must be able to survive intense ultraviolet radiation. Thus, most halophiles have efficient DNA repair and mechanisms to prevent UV damage, including a low number of thymines, the so called UV “targets,” in their genomes. (Alexander Soloviev)


Although halophile archaea can be aerobic or anaerobic, those that need to utilize oxygen have adapted to the low O2 levels in their current enviornments. Besides being chemoheterotrophs, these halophiles, an example being halobacterium, also form gas vessels in these low O2 conditions and thus allow cells to float to the surface where there is more sunlight and oxygen, enabling them to more efficiently produce energy.(http://www.mcponline.org/content/2/8/506.full)

14.) Internal Circulation
The archaea have a system where trap light energy and use it in the form of ATP. They do this without using any chloropyll and when oxygen is in a short supply. What happens is the archaea uses their retinal pigment (which are also found in the vertebrate eye) and combined with a protein to form a molecule that absorbs light called the mircrobial rhodopsin.
external image Rhodopsin-ATP_production_small.jpg
The proton [[#|pump system]] that converts light into chemical energy using rhodopsin. (GC)

15.) Chemical Control
Halophile archaea are unicellular, so have no complex endocrine system, but each unicellular organism does expend energy in maintaining a chemical balance. Because they tend to live in extremely saline conditions, they must expend energy to expel salt from their system and keep environmental salt out. This prevents desiccation.

Review Questions:
1.Halophile archaea use this pigment that combines with a protein to give the archaea microbial rhodopsin that is can use to grow?
2. Since halophile archaea has not evolved to utilize chlorophyll to form ATP, explain how the halophile archaea would produce ATP? Explain how this process differs from the way a plant will trap light and produce ATP.
3. What kind of environmental conditions do Halophile Archaea thrive in?
4.What is the name of the mechanism Halophile Achaea use to allow them to live in conditions with high salt concentrations, and describe specifically how that mechanism works?
5. How have halophile archaea survived despite not having developed protective mechanisms?
6. What does the halophile archaea have that allows it to maintain homeostasis (internal pressure and nutrient retention) and what is it usually made of?

Works Cited
1.) "Bergey's Manual of Systematic Bacteriology." Google Books. N.p., n.d. Web. 13 Dec. 2012.
2.) "Halophile." Wikipedia. Wikimedia Foundation, 14 Dec. 2012. Web. 13 Dec. 2012.
3.) Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life. Sudnerland, MA: Sinauer, 2012.
4) "Microbial Life in Hypersaline Environments." Hypersaline Environments. N.p., n.d. Web. 21 Dec. 2012.http://www.cas.muohio.edu/~stevenjr/mbi202/archaea202.html
5) Krieg, Noel (2005). Bergey's Manual of Systematic Bacteriology. US: Springer. pp. 21–6.