The influence of microbes on the uranium speciation under aerobic and anaerobic conditions

Bacteria belong to the most widely spread organisms in nature. Besides archaea, these organisms represent the only form of life which can inhabit hostile like designated nuclear waste disposal sites. Since bacteria are known to have a considerable impact on radionuclide migration, it is of importance to characterize the U(VI) interaction with dominant bacterial strains isolated from such sites.
In this study, as microbial representatives from actually discussed potential geological formations for nuclear waste storage, one isolate from granite rock (Äspö Hard Rock Laboratory, Sweden) and another bacterial strain from clay (Mont Terri Rock Laboratory, Switzerland), which we have recently isolated and been able to cultivate, are investigated. Concretely, the Gram-negative obligate aerobic Äspö strain P. fluorescens and a species of the Gram-positive facultative anaerobic genus Paenibacillus are examined regarding their interaction with uranium and compared.
Following results will be presented for both mentioned strains:
a) U(VI) accumulation in dependence on [U(VI)]initial, [dry biomass] and pH, b) U(VI) speciation determined by TRLFS, c) phosphate liberation in dependence on [U(VI)], and d) potentiometric titration. Furthermore this work differentiates between metabolically active and rather inactive cells. In addition, the influence of different cell wall structures and oxygen availability on U(VI) interaction will be assessed.
The results on direct interactions of U(VI) with the Äspö strain P. fluorescens will finally be compared with our previous studies exploring indirect U(VI) interactions with pyoverdine-siderophores secreted by this strain. Through this, the influence of indirect U(VI) interactions in comparison to direct interaction mechanisms can be judged.

This work was funded by the BMWi under contract number: 02E10618.