Hyperthermophilic archaea

In the hyperthermophilic Archaea, NAD(P)-reactive enzymes are involved in recycling the reduced cofactors to produce H2 as a waste product as in the case of the NADPH oxidising hydrogenases from the hyperthermophilic Archaea, e.g. Pyrococcus species (Bryant and Adams 1989 Pedroni et al. 1995) and Thermococcus litoralis (Rakhely et al. 1999). These enzymes are also heterotetramers (Fig. 2.2C) with an apparently similar organisation of subunits and prosthetic groups to the Eubacterial examples of Group 5. 

The pharmaceutical and fine chemical industry might use pure hydrogenase or partially purified enzyme preparations in bioconversion applications such as regio and stereoselective hydrogenation of target compounds (van Berkel-Arts et al. 1986). Enzymes are able to catalyse such stereospecific syntheses with ease. However, the cofactors for the NAD-dependent oxidoreductases are expensive. The pyridine nucleotide-dependent hydrogenases such as those from Ralstonia eutropha and hyperthermophilic archaea (Rakhely et al. 1999) make it possible to exploit H2 as a low-cost reductant. The use of inverted micelles in hydrophobic solvents, in which H2 is soluble, has advantages in that the enzymes appear to be stabilized. 

Methanogenesis H2 C02 OO2, possibly formate, acetate 4H2+ CO2 CH4 + 2H2O (CO2 reduction) CH3COOH CH4 + CO2 (acetate fermentation) Mesophilic to hyperthermophilic archaea at vents and seeps... 

Hydrogen oxidation Iron reduction H2 Organic acids N03- Fe - (oxyhydroxides) OO2 Organic acids Identified from molecular analyses Mesophilic bacteria and hyperthermophilic archaea... 

Fermentation Organic compounds Organic compounds Organic compounds CH3COOH CH4 + CO2 Mesophilic and thermophilic bacteria hyperthermophilic archaea... 

Stetter, K.O. Huber, R. BlQchl, E. Kurr, M. Eden, R.D. Fielder, M. Cash, H. Vance, I. (1993) Hyperthermophilic archaea are thriving in deep North Sea and Alaskan oil reservoirs. Nature, 365,743-5. 

S. Ohshima, T. Biochemical characterization, cloning, and sequencing of ADP-dependent (AMP-forming) glucokinase from two hyperthermophilic archaea, Pyrococcus furiosus and Thermococcus litoralis. J. Biochem., 128, 1079-1085 (2000)... 

The hyperthermophilic archaea of the genus Thermococcus, isolated from marine hydrothermal systems, has been found to be a rich source of cyclic methylene-sulfur [135]. The prokaryotic archaea, established as the third domain of life in addition to eukaryotes and bacteria, grow under extreme conditions such as the absence of oxygen, temperatures of 100 °C and saturated salt solutions. Thus, 23 cyclic polysulfides (145-167) could be isolated from the intact cells of Thermococcus tadjuricus (strain Ob9) and T. mococcus acidaminovorans (strain Vc6bk) by using chemical screening methods. 

Kong, H., R.B. Kucera and W.E. Jack 1993. Characterization of a DNA polymerase from the hyperthermophile archaea Thermococcus litoralis Vent DNA polymerase, steady state kinetics, thermal stability, processivity, strand displacement, and exonuclease activities. J. Biol. Chem. 268 1965-1975. 

S. Mukund, Biochemical and Biophysical Characterization of Novel Tungsten-Containing Enzymes from Hyperthermophilic Archaea (Pyrococcusfuriosus, Thermococcus litoralis). Ph.D. Thesis, University of Georgia, Athens (1996). 

Jannasch, H.W. (1997). Two new hyperthermophilic Archaea from mid-Atlantic hydrothermal vents. RIDGE Events 8(2), 22-23... 

The ability of the hyperthermophilic glycosynthases to promote the synthesis of oligosaccharides is a clear example of how the unique characteristics of stability to high temperatures and acidic pH of the glycosidases from hyperthermophilic archaea allows the development of a novel strategy for the chemo-enzymatic synthesis of oligosaccharides. 

Jolivet, E., Corre, E., L Haridon, S., Forterre, P., and Prieur, D. 2004. Thermococcus marinus sp. nov. and Thermococcus radiotolerans sp. nov., two hyperthermophilic archaea from deep-sea hydrothermal vents that resist ionizing radiation. Extremophiles 8 219-227. 

Other organic solutes found in thermophilic archaea likely play roles as thermoprotectants, although there have been few in vitro studies in which the effects of these solutes on protein stability have been tested. Among the putative thermoprotectants in hyperthermophilic archaea is di-myo-inositol-1,1 -phosphate (DIP) (see figure 6.2 for the structure of this... 

Another remarkable feature of the cell membranes of hyperthermophilic archaea is their ability to maintain a liquid-crystalline state over extremely wide ranges of temperature (Horikoshi and Grant, 1998). The exact biophysical basis for this impressive degree of eur-ythermy is not fully understood, albeit the unusual membrane-spanning tetraether lipids could play a role. 

Huber, R., Sacher, M., Vollman, A., Huber, H. Rose, D. (2000). Respiration of arsenate and selenate by hyperthermophilic Archaea. Systematic and Applied Microbiology, 23, 305-14. 

Chen, L., Spiliotis, E., and Roberts, M.F., 1998, Biosynthesis of Di-myo-inositol-1,1 -phosphate, a novel osmolyte in hyperthermophilic archaea. J. Bacteriol. 180 3785-3792. 

Table 2 Percentage of charged amino acids and (G - - C) content of 10 hyperthermophilic archaea (A), 2 hyperthermophilic bacteria (B), and mesophilic bacteria E. coli. A strong prevalence of lysine over arginine in proteomes of hyperthermophiles is obtained for nine organisms. A bold font marks the exception from the general trend...

Although very attractive, the suggestion that hyperthermophilic archaea possess special protein equipment for heat protection or repair of heat-induced damage at extreme temperatures is based only on a few findings. 

Not only functional but also structural proteins from archaeal thermophiles are of economic interest. Thus, the S-layer proteins of thermophilic archaea possess some technical potential. As outlined by Sleytr and Sara [76], the S-layers of different members of bacteria are suitable as molecular sieves. The presumed robust S-layers of the hyperthermophilic archaea will certainly enlarge their applicability. 

---