Responses of the bacterial community to chronic gamma radiation in a rice paddy ecosystem

Purpose: Public concern about radiation protection of the environment and non-human species is increasing. The potential impact of chronic gamma radiation on the bacterial community in a rice paddy ecosystem was investigated. Materials and methods: Paddy field microcosm samples were continuously exposed at a dose rate of 1 Gy day^-1 for five days after which the bacterial community structures in them were compared with those of unirradiated control samples by denaturing gradient gel electrophoresis (DGGE) of the 16S ribosomal ribonucleic acid (rRNA) gene. Dissolved ions in ponding waters of the microcosm samples were determined by ion chromatography. Results: The DGGE band profiles were clearly different between the control and exposure samples. Sequencing of selected DGGE bands revealed that a specific species of the genus Clostridium and of the genus Massilia were grown under radiation exposure. Additionally, the concentrations of sulphate ion in the ponding water of the microcosm samples increased under radiation exposure. Concentrations of Na⁺, Ca ²⁺, and F^- inversely decreased. Conclusions: The data presented suggest that chronic gamma radiation affects the bacterial community structure and material cycles in the rice paddy ecosystem.