Oxidation of elemental sulfur by Sulfolobus acidocaldarius

Oxidation of elemental sulfur by Sulfolobus acidocaldarius, an autotroph which grows at high temperatures and low pH, was examined by use of (35)S-labeled elemental sulfur. When cultured at pH 3.2 and 70 C, S. acidocaldarius oxidized elemental sulfur essentially quantitatively to sulfuric acid. Oxidation rate paralleled growth rate and decrease in pH of the culture medium. Elemental sulfur was not oxidized under these conditions if the culture was poisoned with formaldehyde. During the growth phase, the proportion of cells attached to the sulfur crystals increased progressively, and in the later phases of growth over 10 times more cells were attached to sulfur than were free. Doubling times for eight strains growing on elemental sulfur varied from 37 to 55 h. The organism grows much more rapidly on yeast extract than on sulfur. In a medium containing both sulfur and yeast extract, sulfur oxidation was partially inhibited, although growth was excellent.