Effects of gamma-irradiation on soil bacterial community

Soil bacteria play a vital role in the functioning of ecosystem such as nutrient cycling, organic matter formation and decomposition, soil structure formation, and plant growth promotion. In general, the effect of ionizing radiation on bacteria has been studied by conventional methods based on cultivation of isolated bacteria. Nowadays it is well known that more than 90% of the bacteria existing in soil cannot be cultured under laboratory conditions. A vast portion of soil bacterial communities, therefore, remains unstudied. To overcome the drawbacks of these culture-dependent methods, molecular techniques are widely used approach in the last decade. In the present study, denaturing gradient gel electrophoresis (DGGE) based on the 16S rRNA gene sequence was applied to estimate the effect of ionizing radiation on soil bacterial community.<BR> Gray lowland soil was collected from a paddy field and was flooded with well water. The flooded soil samples were exposed to chronic gamma radiation for 10 days. The dose rate was approximately 1 Gy/day. For a control, samples were shielded from exposure to gamma radiation by lead blocks 10 cm of thickness. After the end of the exposure, DGGE analysis was carried out.<BR> DGGE analysis showed the presence of bacterial species grown specifically in the irradiated samples, suggesting that changes in bacterial community structure occurred by the exposure of gamma radiation. Radiation sensitivity of bacteria in natural soil may be higher than previously thought.