Combination of spectroscopic methods for the identification of U(VI) spezies formed by selected bacteria, algae and fungi

Microorganisms like bacteria, algae and fungi have a significant influence on the immobilization, mo-bilization and transport of radionuclides like uranium and other heavy metals in the biological and geological environment via the soil and water path. To understand the mechanisms of uptake, trans-port, deposition, degradation and the behavior of actinides in different biological and geological sys-tems structural knowledge about the formed actinides species are of great importance and are essential for a reliable assessment of these processes.
Arthrobacter (bacteria), Chlorella vulgaris (green algae) and Schizophyllum commune (fungi) bind significant amounts of uranium(VI) in the pH range from 4 to 7 and contact time of two days. Trans-mission electron microscopy and scanning electron microscopy investigations showed mainly interac-tions of uranium with parts of cell walls of the selected biomass. By investigations of transparent fun-gal cells were identified additionally uranium containing accumulates inside originally living cells.For the determination of the functionalities, which are important for the binding and mobilization or immobilization of uranium, the interaction of uranium(VI) with metabolic active bacterial, algal and fungal cells was investigated by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure spectroscopy (EXAFS). The measured luminescence spectra of uranyl containing cell species of all investigated organisms show bathochromic shifts of the uranyl emission bands in comparison to the corresponding emission signals of the uranyl species in the initial solution independent of the uranium concentration and the pH value of the solution. The com-parison of the obtained biomass spectra with luminescence properties of uranyl model compounds demonstrated the carboxylic and organic/inorganic phosphate groups are responsible for uranium binding on the biomass with varying contributions dependent on the microbial biomass, cell status and uranium concentration in the initial sorption solution. The dominant interaction of uranium(VI) with organic/inorganic phosphate groups could be verified by corresponding EXAFS investigations.