Interaction of Desulfovibrio aspöensis with Actinides

Investigations of processes involving actinides and bacteria in environments around nuclear waste repositories are needed for improvement of the scientific basis for performance of safety assessments. Sulfate reducing bacteria (SRB) are of special interest due to their ability to reduce many metals and actinides. Motamedi and Pedersen showed that SRB are frequently distributed in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (HRL, Sweden) [1]. The presented work is focussed on interactions of curium (III) and uranium (VI) with the strain Desulfovibrio äspöensis, DSM 10631T, recovered from the deep granitic groundwater at the Äspö site [1].
The interaction of D. äspöensis with Cm (III) was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. No evidences were found for changes in the oxidation state of Cm (III). At pH 3, no interaction between Cm (III) and bacteria was detected. With increasing pH, a surface complexation of Cm (III) occurs at the cell walls. The Cm (III)/bacteria surface complex is characterized by its emission spectrum (peak maximum at 600 nm) and its fluorescence emission lifetime (160 ± 15 µs).
80 % of the U (VI), solved initially (0.02 mM) in a liquid medium supplemented with lactate (10 mM) and bacterial biomass (1.10 g/L), was removed by the cells of D. äspöensis after 72 h of incubation at pH 5. Kinetic studies showed that the main amount of U (VI) was removed from the medium during the first 24 h. The microbial activity depended on pH, initial U (VI), and biomass concentration. By using X-ray absorption spectroscopy (XAS), we demonstrated that, in contrast to the above mentioned case with Cm (III), changes of the oxidation state of U (VI) in the precipitate formed by D. äspöensis occurred. The cellular localization of uranium removed from the medium was studied by using Transmission Electron Microscopy (TEM) and Electron-Disperse X-ray (EDX) analyses.

[1] Motamedi, M., Pedersen, K., Int. Syst. Bacteriol. 1998, 48, 311-315.

This work was funded by the BMWi under contract number: 02E9491.The authors are indebted for the use of the 248Cm to the U.S.. Department of Energy, Office of Basic Energy Sciences, through the transplutonium element production facilities at Oak Ridge National Laboratory which was made available as part of a collaboration between FZR and the Lawrence Berkeley National Laboratory (LBNL).