Ecology of sulfur-oxidizing bacteria in hot acid soils

Hot acid soils in Yellowstone National Park are rich in elemental sulfur and harbor extensive populations of sulfur-oxidizing bacteria. Thiobacillus thiooxidans is found at temperatures below 55 C, and at temperatures from 55 to 85 C Sulfolobus acidocaldarius is present. The distribution of these bacteria as a function of temperature was measured by a most-probable-number dilution method, and their activity in situ was assessed by use of a new technique permitting measurement of (14)CO(2) fixation. From these data it is concluded that sulfur-oxidizing bacteria are responsible for production of sulfuric acid in these acidic thermal habitats. Physical and chemical parameters of this unusual soil habitat were also measured and are described.