Two contrary modes of chemolithotrophy in the same archaebacterium.

Sulphur-dependent archaebacteria, which are found around nearly boiling continental solfataric springs and mud holes, can be assigned to two distinct branches: the aerobic, sulphur-oxidizing Sulfolobales and the strictly anaerobic sulphur-reducing Thermoproteales. Here, we report the isolation of a group of extremely thermophilic solfataric archaebacteria that are able to grow either strictly anaerobically by reduction, or fully aerobically by oxidation of molecular sulphur, depending on the oxygen supply. We have also established that the ability to grow in these two ways is shared by Sulfolobus brierleyi, a well-known less thermophilic sulphur-oxidizing archaebacterium capable of ore-leaching. The phenomenon may be dependent on a fundamental switch in genome expression. These organisms might represent the primitive fore-runners of sulphur-oxidizing archaebacteria, meeting their energy requirements either by oxidation or by reduction of the same element.