Pu interaction with bacterial isolates from Mont Terri Opalinus Clay

For the long-term safety assessment of a nuclear waste repository it is necessary to know which microorganisms are present in the potential host rocks (e.g., clay) and how these microorganisms can influence the performance of a repository. The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock for nuclear waste disposal (1). It is well known that indigenous bacteria in such underground environments can affect the speciation and the mobility of actinides (2-4).
In this study, the unknown interaction between Pu and Sporomusa sp. MT-2.99 and Paenibacillus sp. MT-2.2 cells were explored in aqueous solution at pH 6. Both bacteria were isolated from Mont Terri Opalinus clay core samples. The time-dependent Pu concentrations measured in the supernatants were successfully fitted with bi-exponential decay functions. The time-dependent Pu oxidation state distributions were successfully fitted by using mono-exponential decay or growth functions.
To conclude, a moderate to strong impact of Sporomusa sp. and Paenibacillus sp. cells on the Pu speciation was observed. Differences in the Pu interaction process of both strains for instance depend on the presence or absence of an electron donor were detected and will be discussed in detail.

REFERENCES
1. M. Thury, P. Bossart, “The Mont Terri Rock Laboratory, a new international research project in a Mesozoic shale formation, in Switzerland” Eng. Geol., 52, 347-359 (1999).
2. J.R. Lloyd, G.M. Gadd, “The Geomicrobiology of Radionuclides” Geomicrobiol. J., 28, 383-386. (2011).
3. L. Lütke, H. Moll, V. Bachvarova, S. Selenska-Pobell, G. Bernhard, “The U(VI) speciation influenced by a novel Paenibacillus isolate from Mont Terri Opalinus clay” Dalton Trans., 42, 6979-6988 (2013).
4. M.P. Neu, G.A. Icopini, H. Boukhalfa, “Plutonium speciation affected by environmental bacteria” Radiochim. Acta, 93, 705-714 (2005).