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Abstract

Hyperthermophilic sulfate-reducing microorganisms were first isolated from anaerobic submarine hydrothermal systems at Vulcano and Stufe di Nerone, Italy, by Stetter et al. (1987). The isolates were identified as Archaea by 16S-rRNA sequence comparisons and by characteristic features such as the presence of phytanyl ether lipids, lack of a peptidoglycan cell wall, the possession of a rifampicin- and streptolydigin-resistant multicomponent RNA polymerase, the inhibition of DNA synthesis by aphidicolin, and the demonstration of an NAD-dependent ADP ribosylation of a soluble protein catalyzed by diphtheria toxin. Evidence for dissimilatory sulfate reduction was obtained by the demonstration of growth dependence on sulfate and of the formation of large amounts of H2S. The isolates could grow on molecular hydrogen (or formate) and sulfate as sole energy sources, indicating that sulfate reduction is coupled with energy conservation (Thauer et al., 1977). These results established without doubt the existence of Archaea, which can use sulfate as external electron acceptor for anaerobic respiration, a physiological trait previously thought to be restricted to the domain bacteria (Widdel, 1988).