The respiratory system of Sulfolobus acidocaldarius, a thermoacidophilic archaebacterium

The respiratory properties, cellular ATP content and absorption difference spectra of Sulfolobus acidocaldarius (DSM 639) have been investigated. In contrast to earlier postulates regarding Thermoplasma acidophilum [(1984) Syst. Appl. Microbiol. 5, 30-40], S. acidocaldarius seemed to depend energetically on respiration-coupled phosphorylation. Its ATP content strictly depended on respiratory activity. Its membrane is capable of proton pumping and presumably contains a branched electron transport system. The latter is composed of at least 2 types of cytochromes, an a+- and presumably an o-type, while c-type cytochromes could not be detected. It appears possible that one of the terminal oxidases is directly reduced by the socalled caldariellaquinone, found in the same organism [(1983) Syst. Appl. Microbiol. 4, 295-304].