Five new isolates of archaeal coccoid thermoacidophiles were obtained from Icelandic solfataric fields. They are strict chemolithoautotrophs gaining energy by oxidation of S° and sulfidic ores. The new strains grow between 50 and 75 °C and p H 1 and 4.5 and tolerate N a C l concentrations of up to 3.0%. The G C - content of their D N A is 38 m o l % . The new isolates resemble members of Sulfolobus in their morphology, their ability to oxidize reduced sulfur compounds and their GC-content. They are different in their strictly chemolithoautotrophic mode of life, their ore-leaching capacity, D N A / D N A hybridization and incomplete serological cross-reaction of R N A polymerase. Therefore, we describe here a new species, Sulfolobus metallicus. Type strain is Sulfolobus
metallicus (Kra 2 3 ; D S M 6482).