archaea

Archaea
 * Jacob Spitzer**



What comes to mind when you read the word “Archaea”. If you thought of ancient, old archaic, not fun at all, think again! While they’re name derives from they’re very early beginnings in the history of life, they are by no means over the hill. On the contrary, archaea are the most extreme adventure seeking pieces of life we have ever known! Seeking only the hottest saltiest environments, archaea live on the edge, which is why they are known as “extremophiles” – lover of extremes.

Diagnostic Characteristics: Archaea are prokaryotes, so:


 * They have no nucleus, just a nucleoid region where DNA float
 * They have no membrane bound organelles
 * They have circular chromosomes

Archaea share a common ancestor with eukaryotes before bacteria, so:


 * Their membranes contain some complex hydrocarbons
 * They use the amino acid methionine to start protein synthesis
 * Their growth is not inhibited by antibiotics

Archaea are unique in that they are able to grow in environments with temperatures higher than 100◦ C and salinity up to ten times sea level. So extreme!

Archaea are all microbes, meaning they are too small to be seen without a microscope. Unlike bacteria, Archaea has histones associated with their DNA (like eukaryotes). Also like eukaryotes and unlike bacteria, Archaea use methionine as their start codon in protein synthesis. Unlike the 1970s, bacteria and archaea were classified together, but now have been separated into different kingdoms, as they are clearly very different (CSR [|15], [|16]).

Habitats :



Archaea are known for inhabiting the most extreme environments. Hot water geysers, lakes with incredibly high salt concentrations, and oxygen deprived environments like swamps are all home to archaea. Recently it was found that archaea thrive abundantly in moderate environments just as much as in extreme ones, so in fact, archaea are everywhere there is water!

media type="youtube" key="M2wnLJifXB0?fs=1" height="385" width="480"(MC)

Some live near rift vents in the deep sea at temperatures well over 100 degrees Celsius. Others live in hot springs or in extremely alkaline or acidic waters. They have been found inside the digestive tracts of cows, termites, and marine life where they produce methane. They live in the anoxic muds of marshes and at the bottom of the ocean, and even thrive in petroleum deposits deep underground. (CC) ([|7]) Many Archaea are Chemoautotrophs meaning they use energy derived from oxidizing minerals to survive. [[|2]] (LJ) Although archaea are known for living in extreme habitats, they don't have to live there. Scientists are now finding out that they are abundant in plankton that are found in the open ocean. (20)(SM)

Major Types: There are three major kinds of archaea: Methanogens, extreme halophiles, extreme thermophiles.

Methanogens are unique in that they breathe differently from everyone else. They take in carbon dioxide (CO2) and hydrogen (H2), and release methane (CH4) as a waste product. Methanogens, always the misfits, are completely poisoned by oxygen, so they can only live in swamps or marshes where there is little to no oxygen. Methanogens also live in the digestive tracts of cows, termites, and marine mammals. [|1] (NI) Methanogens are really cool in how they work, but unfortunately they are large contributors to global warming, as methane is a major greenhouse gas. Some Methanogens use a florescent pigment for energy to help convert CO2 and H2 into CH4. (MLK) [|1]

Extreme Halophiles love salt. They are described as species that range anywhere from tolerating salt to needed a concentration of salt ten times saltier than sea water to prosper. Halophiles are also known for the red color they reflect. "High salinity represents an extreme environment that relatively few organisms have been able to adapt to and occupy. Most halophilic and all halotolerant organisms expend energy to exclude salt from their cytoplasm to avoid protein aggregation or in other words, 'salting out’. In order to survive the high salinities, halophiles employ two differing strategies to prevent desiccation or state of extreme dryness through osmotic movement of water out of their cytoplasm. Both strategies work by increasing the internal osmolarity of the cell." [MS] [|1]

Halophiles. (SI)(22)

Extreme Thermophiles love heat. For most extreme thermophiles, optimal temperate is 60-80 degrees Celsius. They live near hot sulfur springs or deep-sea hydrothermal vents where few other species could survive. Thermophiles are classified into obligate and facultative thermophiles. Obligate thermophiles require high temperatures for growth, whereas facultative thermophiles can thrive at both high and low temperatures. (DB). Extreme thermophiles that are obligate anaerobes use sulfur as the final electron acceptor during the ETC of their cellular respiration instead of oxygen. Their metabolic chemical reaction is Organic Compound + SulfuràHydrogen Sulfide + Carbon Dioxide (SD) (1).



Archaea are also split up into Euryarchaeota, which includes the halophiles and the methanogens, and Crenarcheota, which includes the thermophiles.

Basic Anatomy:

(MT)

Transport of Materials: Archaea transport materials through passive transport. This means that materials move into the cell when there is a lower concentration inside the cell than outside. This requires no work or ATP expenditure, but means that the cell may be susceptible to bursting if they are placed in an area with too high a concentration of water. Luckily, archaea have developed cell walls to protect against such a disaster.
 * Archaea have the basic characteristics of prokaryotes:
 * The most common forms of archaea are spheres, rods and helices
 * Archaea are normally unicellular, but they may group together to form large colonies
 * Most archaea are 1-5 μm long, about a tenth the size of most eukaryotic cells.
 * Archaea have a cell wall to protect them and maintain their shape, as well as keeping them from exploding if too much water gets in
 * Archaea also produce a sticky capsule to adhere to other surfaces. They may also use pili to attach to other cells.
 * About have of all archaea use flagella, threadlike strands resembling tails that shake back and forth to propel the cell, for directional movement. It consists of a filaments extending outside the cell. Unlike bacterial flagella, which are powered by a flow of hydrogen ions, Archaean flagella are powered by ATP. Also unlike bacteria, Archaean flagella grow form the base. (KL)([|12])
 * DNA in the cell is concentrated in one knotted fiber that rests in a nucleoid region. There is no actual nucleus. DNA may also be included in smaller rings called plasmids.
 * Archaea are pretty diverse in their shape considering they are such small organisms. Some are spherical, a form known as coccus, and these may be either round or lobed and lumpy. Some are rod-shaped, a form known as bacillus. These range from short bar-shaped rods to long slender hair-like forms. (AK) (11)
 * As well as coccus, and bacillus, there have even been some square and triangle shaped Archaea, but these are very unique. (RG) [17]

Reproduction:



Archaea reproduce asexually by binary fission; they split apart. Archaea do not go through mitosis, as eukaryotes do, because mitosis requires the splitting of a nucleus, which archaea don’t have. Prokaryotes like archaea can transmit genes fairly easily from cell to cell, either by picking them up from the environment, transferring them directly, or transferring them through viruses. Archaea reproduce very quickly, so mutations allow them to adapt much more quickly than eukaryotes. In an unlimited environment, archaea populations double every generation (1-3 hours). Mutation is very important for genetic variation. Without mutations, archaea populations wouldn't be able to adapt to environmental changes resulting in an altering of natural selection. (SR) (23) Although Archaea do not have nucleus, they still have chromosomes because they have unique binding proteins that are similar to histones. First the genome replicates. The identical copy and the original end up at opposite ends of the cell. Furrowing, pinching in the middle of a cell to produce two new cells, occurs. Archae also have smaller circular DNA that are essential to life, and that as well is also complicated. (NG)

Environmental Adaptations: It was originally thought that archaea had adapted to be able to thrive in extreme environments such as hot water geysers but in fact, they may be able to live in these environments because of they’re origins. Archaea first formed billions of years ago when the earth was still a place of extremely high temperatures. It is speculated that archaea have always been able to survive in these environments and have moved into more moderate marine environments when cooler waters came around. Other characteristics they have adapted are cell walls to avoid bursting and offer protection, pili to attach to other cells, and flagella to get around better. It has recently been found that certain archea can survive in a pH of near zero, this archea is called // Picrophilus torridus //. Other types thrive in salty lakes and can compete and outlive or out-compete bacteria in watersources with a salinity level above 20%. Most Archea tend to live in waters of 45 degrees Celsius or higher. (GR) [|21]

How do we benefit? Firstly, archaea are involved in the major cycles of elements and so life itself would not exist without archae. In addition, archaea’s ability to thrive in high temperatures is useful for commercial processes. Scientists have added enzymes to detergents so that they can maintain their activity at high temperatures and pH. Also, scientists have used enzymes from Archaea to convert corn starch into dextrins. Certain archae can also be used for cleaning contaminated areas such as petroleum spills. (MT) (10)

Review Questions: 1. How does Archaea's rate to reproduce effect its ability to adapt to the envrionment? What is the evidence? (CW) 2. What evidence is there to support the hypothesis that archaea first evolved in extreme environments, before adapting to more moderate ones? (ZXU) 3. How does the anatomy of Archaea (the cell wall, its pili and flagellum) protect itself from the environment and help with locomotion? (RG) 4. What is the role of archea in chemical cycling? LW 5. What causes scientists to believe that the domain Archaea is more related to the domain Eukaryotes then to the domain Bacteria? (MF) 6. Name one source of energy for archaea. Why do you think they do this?(ORS) 7. What are the main differences between the three major types? Where might you find each type? (RL)

Sources: Campbell, Neil and Jane Reece. __Biology Sixth Edition.__ San Francisco: Benjamin Cummings 2002. [] [] [] [] [] [] Sources for Edits 1) [] 2) [] 10.[] 11) [] 12) [] (KL) 13. [] 14. [] 15.http://www.earthlife.net/prokaryotes/archaea.html (CSR) 16. http://www.ucmp.berkeley.edu/archaea/archaea.html (CSR) 17. [] 18. [] (NG) 19. http://pathmicro.med.sc.edu/fox/e_coli-dk.jpg (MP) 20. @http://www.ucmp.berkeley.edu/archaea/archaea.html (SM) 21. http://www.eoearth.org/article/Archaea?topic=49508 (GR) 22. http://toyota-manuals.com/pictures-of-halophiles 23.http://www.ucmp.berkeley.edu/archaea/archaea.html (SR)