Research of effects of sulfate reducing bacteria on chemical states of actinides in geological formation

We have been conducting basic sciences on microbial actinides interaction in order to elucidate the environmental behavior of actinides under relevant conditions.Reduction of Pu(IV)to Pu(III)by sulfate reducing bacteria was studied in the presence of citric acids。We found that some fraction of Pu(IV)was reduced to Pu(III)。The effect of AQDS，which was an alternative of humic substances，on the reduction of Pu(IV)was very low。These results indicated that Pu(IV)is reduced to Pu(III)by microbial activity in the geological formation.Effect of desferrioxamine B(DFO)on the sorption of Pu(IV)，Th(IV)and Eu(III)(analog for Am(III))on Pseudomonas fluorescens was studied。In the presence of DFO the sorption of Pu(IV)，Th(IV)and Eu(III)on the cells increased with a decrease in pH from7to4.Adsorption of DFO on the cells was negligible in the solution with and without metals.Adsorption of Pu(IV)，Th(IV)and Eu(III)on P.fluorescens cells decreased in the order Eu(III)&gt；Th(IV)&gt；Pu(IV)，which corresponds to increasing stability constant of the DFO complexes.These results indicate that Th(IV)，Pu(IV)and Eu(III)dissociate when in contact with cells，after which the metals are adsorbed.Mechanism of U(VI)mineralization by the yeast Saccharomyces cerevisiae was examined by batch experiment at pH3.2.FESEM-EDS，TEM，and visible diffuse reflectance spectrometry revealed the formation of H-autunite，HUO_2PO_4·4H_2O on the yeast cells.Apparently，the sorbed U(VI)on the cell surfaces reacts with P released from the yeast to form H-autunite by local saturation。These findings indicate that the yeast‘s cell surfaces，rather than the bulk solution，offer the specific conditions for this geochemical process.These findings suggest that bacterial adsorption and mineralization affect environmental behavior of actinides。

We have been conducting basic sciences on microbial actinides interaction in order to elucidate the environmental behavior of actinides under relevant conditions.Reduction of Pu(IV) to Pu(III) by sulfate reducing bacteria was studied in the presence of citric acids. We found that some fraction of Pu(IV) was reduced to Pu(III). The effect of AQDS, which was an alternative of humic substances, on the reduction of Pu(IV) was very low. These results indicated that Pu(IV) is reduced to Pu(III) by microbial activity in the geological formation.Effect of desferrioxamine B (DFO) on the sorption of Pu(IV), Th(IV) and Eu(III) (analog for Am(III)) on Pseudomonas fluorescens was studied. In the presence of DFO the sorption of Pu(IV), Th(IV) and Eu(III) on the cells increased with a decrease in pH from 7 to 4. Adsorption of DFO on the cells was negligible in the solution with and without metals. Adsorption of Pu(IV), Th(IV) and Eu(III) on P.fluorescens cells decreased in the order Eu(III) > Th(IV) > Pu(IV), which corresponds to increasing stability constant of the DFO complexes. These results indicate that Th(IV), Pu(IV) and Eu(III) dissociate when in contact with cells, after which the metals are adsorbed.Mechanism of U(VI) mineralization by the yeast Saccharomyces cerevisiae was examined by batch experiment at pH 3.2. FESEM-EDS, TEM, and visible diffuse reflectance spectrometry revealed the formation of H-autunite, HUO_2PO_4・4H_2O on the yeast cells. Apparently, the sorbed U(VI) on the cell surfaces reacts with P released from the yeast to form H-autunite by local saturation. These findings indicate that the yeast's cell surfaces, rather than the bulk solution, offer the specific conditions for this geochemical process.These findings suggest that bacterial adsorption and mineralization affect environmental behavior of actinides.