A novel, extremely thermoacidophilic, obligately chemolithotrophic archaeon (strain JP7(T)) was isolated from a solfatara on Lihir Island, Papua New Guinea. Cells of this organism were non-motile, Gram-negative staining, irregular-shaped cocci, 0.5-1.5 microm in size, that grew aerobically by oxidation of sulfur, Fe(2+) or mineral sulfides. Cells grew anaerobically using Fe(3+) as a terminal electron acceptor and H(2)S as an electron donor but did not oxidize hydrogen with elemental sulfur as electron acceptor. Strain JP7(T) grew optimally at 74 degrees C (temperature range 45-83 degrees C) and pH 0.8-1.4 (pH range 0.35-3.0). On the basis of 16S rRNA gene sequence similarity, strain JP7(T) was shown to belong to the Sulfolobaceae, being most closely related to the type strains of Acidianus ambivalens (93.7 %) and Acidianus infernus (93.6 %). Cell-membrane lipid structure, DNA base composition and 16S rRNA gene sequence similarity data support the placement of this strain in the genus Acidianus. Differences in aerobic and anaerobic metabolism, temperature and pH range for growth, and 16S rRNA gene sequence differentiate strain JP7(T) from recognized species of the genus Acidianus, and an emendation of the description of the genus is proposed. Strain JP7(T) is considered to represent a novel species of the genus Acidianus, for which the name Acidianus sulfidivorans sp. nov. is proposed. The type strain is JP7(T) (=DSM 18786(T)=JCM 13667(T)).