Thermophilic bacteria/archaea

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

Extremophilic bacteria employ mechanisms analogous to those used by thermophilic members of the Archaea. In some anaerobic thermophilic bacteria, C30 dicarboxylic acids may provide 10-20% of the acyl chains of membrane lipids (Langworthy and Pond, 1986). These acyl chains may be esterified to a glycerol molecule at each end of the C30 chain to form a membrane-spanning lipid with a high ability to stabilize the membrane against thermal perturbation. 

Prokaryotes Bacteria Archaea (methaneogenous, extreme halophiles, extreme thermophiles) 500 - 5.000 nm 100- 15.000 nm... 

An enzyme which may specifically prevent heat denaturation of DNA is thought to be the reverse gyrase [38-41]. Although not specific for archaea, this enzyme seems to be specific for thermophilic prokaryotes (archaea as well as bacteria). The reverse gyrase introduces positive supercoils into double-stranded, covalently closed DNA. But as mentioned by Bouthier de la Tour et al. [41], there is no direct evidence for the involvement of this type of supercoiling in the stability of DNA at high temperature . 

Sulphur reduction -chemolithotrophic h2 s°, s2o32-, SO/- co2 H+ + 4H2 + S042- -4 HS + 4H20 S + H2-4H2S C02 + S042- + 6H2 -4 [CH20] + S2- + 5H20 Mesophilic and thermophilic bacteria hyperthermohilic archaea... 

FIGURE 6.5.1 Hot hydrothermal pools in Kamchatka, Russia, are a fitting environment for thermophilic bacteria and archaea. (From Hoffmann, R., Am. Sci., 89, 20, 2001. With permission.)... 

There is still no crystal structure of a class II RNR. The enzymes isolated from thermophilic bacteria and archaea may be good starting material for obtaining this important information. This is currently under investigation. 

The physical nature of hydrophobic effects was previously considered to be entropic. Based on this hypothesis, it has often been claimed that the thermal stabilization of proteins in thermophiles may be correlated with an increase in the number of hydrophobic residues. A critical analysis proved the differences to be statistically insignificant the recent dramatic increase in sequence data from complete genomes of mesophilic and (hyper-) thermophilic bacteria and archaea clearly confirmed this finding (see below). Considering the real meaning of the word hydrophobic, it is clear that the aversion of nonpolar solutes to water becomes more ordinary and less entropy-driven at extreme temperatures, whereas in the mesophilic temperature regime the hydrophobic effect is indeed entropic. Maximum aversion arises at the temperature at which the ftee energy of transfer of nonpolar solutes into water shows its maximum. Under this condition, the entropy (i.e., the temperature derivative of AG) equals zero, so that the hydrophobic effect must be driven by enthalpic contributions, attributable to van der Waals forces in the core of the protein. ... 

Gobema, M., Insam, H., Franke-Whittle, I. H. (2009). Effect of bio waste sludge maturation on the diversity of thermophilic bacteria and archaea in an anaerobic reactor. Applied and Environmental Microbiology, 75, 2566—2572. 

This key enzyme of the dissimilatory sulfate reduction was isolated from all Desulfovibrio strains studied until now 135), and from some sulfur oxidizing bacteria and thermophilic Archaea 136, 137). The enzymes isolated from sulfate-reducing bacteria contain two [4Fe-4S] clusters and a flavin group (FAD) as demonstrated by visible, EPR, and Mossbauer spectroscopies. With a total molecular mass ranging from 150 to 220 kDa, APS reductases have a subunit composition of the type 012)32 or 02)3. The subunit molecular mass is approximately 70 and 20 kDa for the a and )3 subunits, respectively. Amino-acid sequence data suggest that both iron-sulfur clusters are located in the (3 subunit... 

Not all MIPS enzymes from thermophiles may have divalent metal ion-dependent activities. While crude protein extracts of A. fulgidus exhibited a MIPS activity that absolutely required divalent metal ions and was totally inhibited by 1 mM EDTA, the production of I-l-P from G-6-P (carried out >75 °C) by protein extracts from M. igneus and T. maritima was observed in the presence of 1 mM EDTA. This observation (Chen and Roberts, unpublished results) suggests that either the MIPS from these particular archaea is not divalent metal ion-dependent or that the metal ions bind very tightly and are not easily removed. None of the MIPS activities from thermophiles are affected by the addition ofNELt-1". Since the divalent cation in A. fulgidus MIPS has been suggested to aid in the aldol condensation and since this is supposedly done by NH4+ in the yeast enzyme, it is of interest how this step occurs in the other archaea and bacteria. 

Further studies indicate that an ADP-forming acetyl-CoA synthetase is also operative in other extremely thermophilic archaea Pyrococcus woesei, Thermococcus celer, Hyperthermus butylicus, Desulfurococcus amylolyticus), which form acetate as end product of their fermentation [305]. In contrast, in acetate forming (eu)bacteria, acetate formation from acetyl-CoA and the synthesis of ATP from ADP and Pj are catalyzed by two enzymes phosphate acetyltransferase and acetate kinase. This holds true for the extremely thermophilic (eu)bacterium. Thermotoga maritima[3Q5], which ferments... 

The universality of the heat shock response has been proved by comparative studies not only within the domains of bacteria and eucarya but also, more recently, within the domain of archaea. Thus the phenomenon of acquired thermotolerance associated with the synthesis of specific proteins could also be found in mesophilic and thermophilic archaea [49-52]. 

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. 

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