From a solfataric field in Italy three isolates of spherical thermoacidophilic metal-mobilizing archaebacteria were obtained. They are facultative autotrophs. From sulfidic ores they extract metal ions with very high efficiency. They are also vigorous S°-oxidizers. Alternatively, they are able to use heterogeneous organic material such as yeast extract. The isolates grow within a temperature ränge from 50 to 80 °C. The
GC-content of their DNA is 45 mol %. No significant D N A homology is detectable between the isolates and the type strains of the members of the genera Acidianus and Sulfolobus. The DNA-dependent RNA Polymerase of isolate TH2 shows incomplete serological cross-reaction with antibodies against the enzyme of Sulfolobus acidocaldarius. On the basis of the distinct physiological and molecular properties we describe the new strains as members of the new genus Metallosphaera. Type species and type strain is Metallosphaera sedula (TH2, DSM5348).