出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/14 18:55:38」(JST)
| Pyrococcus furiosus | |
|---|---|
| Scientific classification | |
| Domain: | Archaea |
| Kingdom: | Euryarchaeota |
| Phylum: | Euryarchaeota |
| Class: | Thermococci |
| Order: | Thermococcales |
| Family: | Thermococcaceae |
| Genus: | Pyrococcus |
| Species: | P. furiosus |
| Binomial name | |
| Pyrococcus furiosus Erauso et al. 1993 |
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Pyrococcus furiosus is an extremophilic species of Archaea. It can be classified as a hyperthermophile because it thrives best under extremely high temperatures—higher than those preferred of a thermophile. It is notable for having an optimum growth temperature of 100°C (a temperature that would destroy most living organisms), and for being one of the few organisms identified as possessing enzymes containing tungsten, an element rarely found in biological molecules.
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The species was taken from the thermal marine sediments and studied by growing it in culture in a lab. Pyrococcus furiosus is noted for its rapid doubling time of 37 minutes under optimal conditions, meaning that every 37 minutes, the number of individual organisms is multiplied by 2, yielding an exponential growth curve. It appears as mostly regular cocci—meaning that it is roughly spherical—of 0.8 µm to 1.5 µm diameter with monopolar polytrichous flagellation. Each organism is surrounded by a cellular envelope composed of glycoprotein, distinguishing them from bacteria.
It grows between 70 °C (158 °F) and 103 °C (217 °F), with an optimum temperature of 100 °C (212 °F), and between pH 5 and 9 (with an optimum at pH 7). It grows well on yeast extract, maltose, cellobiose, β-glucans, starch, and protein sources (tryptone, peptone, casein, and meat extracts). This is a relatively wide range when compared to other archaea. Growth is very slow, or nonexistent, on amino acids, organic acids, alcohols, and most carbohydrates (including glucose, fructose, lactose, and galactose). The metabolic products of Pyrococcus furiosus are CO2 and H2. The presence of hydrogen severely inhibits its growth and metabolism; this effect can be circumvented, however, by introducing sulfur into the organism's environment. In this case, H2S can be produced through its metabolic processes, although no energy seems to be derived from this series of reactions. Interesting to note is that, while many other hyperthermophiles depend on sulfur for growth, P. furiosus does not.
Pyrococcus furiosus is also notable for an unusual and intriguingly simple respiratory system, which obtains energy by reducing protons to hydrogen gas and uses this energy to create an electrochemical gradient across its cell membrane, thereby driving ATP synthesis. Such a system could be a very early evolutionary precursor of respiratory systems in all higher organisms today.[1]
A DNA polymerase was discovered in P. furiosus that is unrelated to other known DNA polymerases, as no significant sequence homology was found between its two proteins and those of other known DNA polymerases. This DNA polymerase has strong 3'-5' exonucleolytic activity and a template-primer preference which is characteristic of a replicative DNA polymerase, leading scientists to believe that this enzyme may be the replicative DNA polymerase of p. furiosus. Although archaea are, in general, more like eukaroyotes than prokaryotes in terms of transcription, translation, and replication of their DNA, scientists have not been able to find many examples of DNA polymerases in archaea that are similar in structure to DNA polymerases of eukaryotes. Obtaining more information about these enzymes would allow a more comprehensive understanding of the mechanism of DNA replication in archaea.[citation needed]
The enzymes of Pyrococcus furiosus are extremely thermostable. As a consequence, the DNA Polymerase from Pyrococcus furiosus (also known as Pfu DNA polymerase) can be used in the polymerase chain reaction (PCR) DNA amplification process.
One practical application of P. furiosus is in the production of diols for various industrial processes. It may be possible to use the enzymes of Pyrococcus furiosus for applications in such industries as food, pharmaceuticals, and fine-chemicals in which alcohol dehydrogenases are necessary in the production of enantio- and diastereomerically pure diols. Enzymes from hyperthermophiles such as P. furiosus can perform well in laboratory processes because they are relatively resistant: they generally function well at high temperatures and high pressures, as well as in high concentrations of chemicals.
In order to make naturally-derived enzymes useful in the laboratory, it is often necessary to alter their genetic makeup. Otherwise, the naturally-occurring enzymes may not be efficient in an artificially-induced procedure. Although the enzymes of P. furiosus function optimally at a high temperature, scientists may not necessarily want to carry out a procedure at 100 °C (212 °F). Consequently, in this case, the specific enzyme AdhA was taken from P. furiosus and put through various mutations in a laboratory in order to obtain a suitable alcohol dehydrogenase for use in artificial processes. This allowed scientists to obtain a mutant enzyme that could function efficiently at lower temperatures and maintain productivity.
The expression of a certain gene found in P. furiosus in plants can also render them more durable by increasing their tolerance for heat. In response to environmental stresses such as heat exposure, plants produce reactive oxygen species which can result in cell death. If these free radicals are removed, cell death can be delayed. Enzymes in plants called superoxide dismutases remove superoxide anion radicals from cells, but increasing the amount and activity of these enzymes is difficult and not the most efficient way to go about improving the durability of plants.
By introducing the superoxide reductases of P. furiosus into plants, the levels of O2 can be rapidly reduced. Scientists tested this method using the arabidopsis plant. As a result of this procedure, cell death in plants occurs less often, therefore resulting in a reduction in the severity of responses to environmental stress. This enhances the survival of plants, making them more resistant to light, chemical, and heat stress.
This study could potentially be used as a starting point to creating plants that could survive in more extreme climates on other planets such as Mars. By introducing more enzymes from extremophiles like P. furiosus into other species of plants, it may be possible to create incredibly resistant species.
By comparing P. furiosus with a related species of archaea, Pyrococcus abyssi, scientists have tried to determine the correlation between certain amino acids and affinity for certain pressures in different species. P. furiosus is not barophilic, while P. abyssi is, meaning that it functions optimally at very high pressures. Using two hyperthermophilic species of archaea lessens the possibility of deviations having to do with temperature of the environment, essentially reducing the variables in the experimental design.
Besides yielding information about the barophily of certain amino acids, the experiment also provided valuable insight into the origin of the genetic code and its organizational influences. It was found that most of the amino acids that determined barophily were also found to be important in the organization of the genetic code. It was also found that more polar amino acids and smaller amino acids were more likely to be barophilic. Through the comparison of these two archaea, the conclusion was reached that the genetic code was likely structured under high hydrostatic pressure, and that hydrostatic pressure was a more influential factor in determining genetic code than temperature.
As Pyrococcus furiosus can withstand large variations in temperature (100+ °C), it is being used to do research into bio-engineering plants suitable for growing in greenhouses on Mars. The research involves taking a gene from Pyrococcus furiosus and introducing into the plant arabidopsis.
Pyrococcus furiosus was originally isolated anaerobically from geothermally heated marine sediments with temperatures between 90 °C (194 °F) and 100 °C (212 °F) collected at the beach of Porto Levante, Vulcano Island, Italy. It was first described by Dr. Karl Stetter of the University of Regensburg in Germany, and a colleague, Dr. Gerhard Fiala. Pyrococcus furiosus actually originated a new genus of archaea with its relatively recent discovery in 1986.
The sequencing of the complete genome of Pyrococcus furiosus was completed in 2001 by scientists at the University of Maryland Biotechnology Institute. The Maryland team found that the genome has 1,908 kilobases, coding for some 2,065 proteins.
The name Pyrococcus means "fireberry" in Greek, to refer to the extremophile's round shape and ability to grow in temperatures of around 100 degrees Celsius. The species name furiosus means 'rushing' in Latin, and refers to the extremophile's doubling time.
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| リンク元 | 「パイロコッカス・フリオサス」 |
| 関連記事 | 「Pyrococcus」 |