Abstract
Surveys were carried out to detect iron-sulfur bacteria in acid sulfate soils, acid river water, and land slide areas. Acid sulfate soils are widely distributed in Japan, where pyrite in the deep layers is exposed to the air during engineering works. Pyrogenic pyrite crystals, 1-5 cm in diameter, were found in the rock under the exposure, at Irihirose Village, Niigata Prefecture. A large number or iron bacteria was counted in the acid soil. The oxidation process of fine pyrite powder was completed in 10 days at 30℃ when the powder was mixed with soil, and the pH values decreased from 3.8 to 2.5 with increasing amounts of sulfate. The iron bacteria multiplied, ranging from 10^4 to 10^8 per gram soil ; the increase of sulfur bactreia was lower than that of iron bacteria. The upper stream of the Tamagawa River has a strong acidity due to the presence of acid cations and anions, Al^<3+>, Fe^<3+>, SO^<2->_4, and Cl^-. Iron-sulfur bacteria found in the acid water disappeared in the neutral water downstream, where a slightly larger number of hetrotrophic bacteria was detected. Bacterial activities for ferrous and thiosulfate oxidation were recognized in landslide areas where the soil exhibited an acid and neutral reaction. The newly devised dilution frequency method can be applied for the detection of iron bacteria in soils. The thiosulfate medium may be useful for the enumeration of sulfur bacteria.
