Samples of river water and of sediment from the surface of submerged stones were taken from the Yonako River, Dodo River and Chikuma River and analyzed for ion species, heavy metals and microbial groups. The water of the Yonako and Dodo Rivers was acidic (pH 3-6) because of the influence of abandoned sulfur mines and the surrounding geological conditions. It is well known that unique and useful bacteria have been found in specific environments, such as volcanic ponds and acidic mine drains. We were interested therefore in the characteristics of microorganisms in the water and the sediment on stones in the Yonako and Dodo Rivers. The concentration of SO42- ions was high in the river water of the Yonako and Dodo Rivers (46 mg/L), and the iron concentration in the stone sediment from the Yonako River was also very high (200 g/kg) compared to that in the Chikuma River and most other rivers. In routine bacteriological agar medium culture, the number of microbial colonies in the Yonako River samples was low compared to the Chikuma River samples. However, using the genetic PCR-DGGE method, it was confirmed that there were many microorganisms living in special environments such as the Yonako River.
