Thermophilic archaebacteria

Fig. 3. Pathways of glucose catabolism in halophilic and thermophilic archaebacteria. The modified Entner-Doudoroff pathway of halophiles (solid lines) and the non-phosphorylated Entner-Doudoroff pathway of Sulfolobus sol/ataricus and Thermoplasma acidophilum (dashed lines) are shown in comparison with the classical Entner-Doudoroff pathway of eubacteria (heavy solid lines) from Fig. 1.

Finally, the need for further investigations into the metabolism of glucose in thermophilic archaebacteria should be stressed. Firstly, the fate of glyceraldehyde in Sulfolobus species needs to be established, and there is still eontroversy coneeming the pathways in Tp. acidophilum. That is, Searcy and Whatley [15] have provided evidence from respiratory studies for the operation of glycolysis in Tp. acidophilum but we have been unable to detect many of the enzymes of this pathway [14]. Secondly, there is a... 

Many of the sulphur-dependent thermophilic archaebacteria can grow autotrophically and, in the two genera where the mechanism of C02-fixation has been studied, there is evidence that it is via a reductive citric acid cycle. 

In their first paper, Kikuchi and Asai [72] reported that S. acidocaldarius contained, besides a reverse gyrase, one ATP-independent and two ATP-dependent thermophilic DNA topoisomerases (including one DNA gyrase). However, their purification procedure lacked a step to remove DNA, so that at least one of the ATP-dependent topoisomerases probably corresponded to the reverse gyrase copurifying with DNA (discussed in ref [74]). Later work did not confirm the presence of a classical gyrase but demonstrated the presence of at least one type II DNA topoisomerase, and probably one ATP-independent type I DNA topoisomerase in Sulfolobus and in other thermophilic archaebacteria. 

Fig. 8 summarizes the different topoisomerase activities discovered up to now in extremely thermophilic archaebacteria. 

Fig. 8. DNA topoisomerases in extremely thermophilic archaebacteria. The arrows with the same shading correspond to homologous DNA topoisomerases, 1 and 2 are for type I and type II DNA topoisomerases, respectively. IV > 0, positive supercoiling W <0, negative supercoiling.

Attempts have been made recently to analyze directly the topological state of chromosomal DNA in extremely thermophilic archaebacteria. A nucleoid-like structure has been isolated from S. acidocaldarius using procedures similar to those previously used to analyze DNA topology of E. coli chromosome [32,33,38,39]. Unfortunately,... 

We close this survey of cell membranes with a remarkable observation that adds support to this novel picture of cytomembrane shape. In Chapter 4 (section 4.13), it was noted that many bacteria are shrouded in a mesh-like protein coat, which often displays a regular, crystallographic form. The most exotic examples of bacteria are the thermophilic archaebacteria, that thrive at temperatures between 70°-105°C, in sulfur-rich hot-springs and mud holes. (So anachronistic are these single-celled organisms, that they are sometimes taxonomically classified as a distinct Kingdom.) It appears that the dimensions of the protein layers in species of these bacteria, Solfolobus solfataricus, are in "precise epitaxial coincidence" with the lattice parameters of a bicontinuous cubic phase, formed in excess water with the membrane lipids predominant in this organism in vitro) [140]. Such a coincidence is indeed difficult to reconcile with the usual notion of a flat, neutral, cytomembrane, whose sole function is to support the real stuff of life, the proteins. 

Fischer F., Zillig W., Stetter K.O., Schreiber G. (1983) Chemolithoautotrophic metabolism of anaerobic extremely thermophilic archaebacteria. Nature 301, 511-13. 

Stetter, K.O., 1988. Archaeoglobus fulgidus gen. nov., sp. nov. a new taxon of extremely thermophilic Archaebacteria. Systematic and Applied... 

Hamana K, Hamana H, Niitsu M, Samejima K, Sakane T, Yokota A (1994) Occurrence of tertiary and quaternary branched polyamines in thermophilic Archaebacteria. Microbios 79 109-119 Hensel R, Konig H (1988) Thermoadaptation of methanogenic bacteria by intracellular ion concentration. FFMS Microbiol Lett 49 75-79... 

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