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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 aldehyde ferredoxin oxidoreductase enzymes containing tungsten, an element rarely found in biological molecules. == Properties == 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 and , with an optimum temperature of , 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 ''P. 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. ''P. 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.〔Sapra, R; Bagramyan, K; Adams, M. W. W. (2003) A simple energy-conserving system: proton reduction coupled to proton translocation, ''Proc. Natl. Acad. Sci. U.S.A.'' 100:13, 7545–7550. 〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pyrococcus furiosus」の詳細全文を読む スポンサード リンク
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