The U(VI) Speciation Influenced by a Novel Paenibacillus Isolate from Mont Terri Opalinus Clay

Bacterial cell walls have a high density of ionizable functional groups available for U(VI) binding, hence have a great potential to affect the speciation of this contaminant in the environment. The studied strain of the genus Paenibacillus is a novel isolate originating from the Mont Terri Opalinus clay formations (Switzerland) which are currently investigated as potential host rock for future nuclear waste storage. The U(VI) binding by the cell surface functional groups was studied by potentiometry combined with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This paper provides stability constants of U(VI) complexed by cell surface functional groups. Additionally the bacteria-mediated liberation of inorganic phosphate in dependence on [U(VI)] at different pH values was studied in order to assess the influence of phosphate release on U(VI) mobilization. It could be shown that in the acidic pH range (pH 3) UO22+ binding onto the cell envelope is governed by coordination to hydrogen phosphoryl sites. Upon increasing pH an increasing coordination of UO22+ to carboxylic and deprotonated phosphoryl sites occurs. At a pH greater than 7 uranyl hydroxides dominate the speciation. In general, UO22+ is bound to the cell envelope with relatively high thermodynamic stability.