Extremely thermophilic archaebacteria are known to be metabolizers of elemental sulfur and the methanogens. A novel group of extremely thermophilic archaebacteria is described, which consists of sulfate-respiring organisms that contain pure factor 420 and that have been isolated from marine hydrothermal systems in Italy. They possess a third type of archaebacterial RNA polymerase structure previously unknown, indicating an exceptional phylogenetic position. Most likely, this group represents a third major branch within the archaebacteria. The existence of sulfate reducers at extremely high temperatures could explain hydrogen sulfide formation in hot sulfate-containing environments, such as submarine hydrothermal systems and deep oil wells.

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SummaryFrom 85 samples taken during cruise 45B of the R/V SONNE within the Sunda Arc subduction zone and from solfatara fields in Java, thermophilic and hyperthermophilic archaea and bacteria were isolated. The archaea were found to belong to the genera Methanol? act er tum, Methanolobus, Methajtosarcina, Acidianus, Thermoproteus, Desulfurococcus, Thermoplasma, Thermococcus and a so far unknown thermoacidophilic continental metal mobilizer. All 7 Thermoplasma isolates were found to represent a new genotype so far only found in Indonesia. The extremely thermophilic bacterial isolates are a new species of Thermotoga and a novel strict anaerobe, thriving by H2/NOj~ autotrophy.

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