Approximately 100 years ago, contaminated water from the Ashio Copper Mine in Japan spilled out frequently during floods and caused the detrimental effects on surrounding areas. Currently, situations of the heavy metal contamination have been improved due to the recent activities of the government, NPOs and citizen volunteers. However, high amount of heavy metals can be still detected and effects of these heavy metals on organisms are still not clear around the Watarase Retarding Basin. In this study, we investigated the effects of heavy metals on the microbial compositions in the Watarase Retarding Basin. Measurement of heavy metals extracted from the soils sampled at different spots demonstrated that the soil from the previously contaminated spot showed higher level of various heavy metals compared to other spots. In addition, in this spot, soil bacterial composition was changed drastically, indicating that the bacterial communities were affected by the presence of heavy metals in the soil. Especially, Acidobacteria which was reported to exist in chemically polluted areas was abundant. It should be the first report that revealed the effects of heavy metals on microorganisms in the Watarase Retarding Basin.
