The influence of paddy soil drying on Tc insolubilization by bacteria.

Tc insolubilization in four soils samples was compared by pre-incubating them in both dry and wet states, then measuring Tc concentrations in solution when the samples were saturated with an excess of water spiked with 99Tc. Soils pre-incubated in a dry state showed higher Tc insolubilization than soils incubated in a wet state. To clarify the difference in Tc insolubilization, Eh, bacterial abundances, and bacterial species compositions in the dry and wet ponding water samples were determined. For the wet ponding water samples, Eh values were forced to decrease, but no increase in Tc insolubilization was observed. The dry and wet ponding water samples had similar numbers of bacteria. However, denaturing gradient gel electrophoresis analysis revealed that they had different bacterial species compositions. These results suggested the difference in bacterial species compositions would account for the difference in Tc insolubilization.