Thermoplasma acidophilum and Thermoplasma volcanium sp. nov. from Solfatara Fields

Twenty-three isolates of motile, cell wall-deficient, thermoacidophilic archaebacteria were obtained from hot acidic springs, soils and sediments within solfatara fields in the Azores, Iceland, Indonesia, Italy, and the United States. They are facultatively anaerobic organotrophs. Anaerobically, the isolates gain energy by sulfur respiration. The new strains resemble Thermoplasma acidophilum by their highly irregular morphology, the lack of a cell envelope and the presence of a serologically homologous histon-like protein. On the basis of their physiological properties, the GC-contents of their DNA and their DNA homology, the new isolates were found to represent (a) Thermoplasma acidophilum, which has only been isolated from self-heated coal refuse piles, and (b) a new species, Thermoplasma volcanium sp. nov., which comprises three different genotypes with insignificant DNA homology with each other and which is described in this paper. Based on the new isolates, an emended description of the genus Thermoplasma and of Thermoplasma acidophilum is given.