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Influence of biofilms on the migration behavior of radionuclides
Krawczyk-Bärsch, E.; Arnold, T.; Großmann, K.;
Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in the EPS of a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 µm in width and up to 20 µm in length and were located at the bottom and at the edges of biofilms colonies. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm.
Electrochemical microsensor studies of the O2 concentrations within the biofilm identified depleted zones closer to the biofilm/air interface which may trigger uranium redox processes. The microsensor profile measurements in the stable multispecies biofilms exposed to uranium in ecologically relevant concentrations (1x10-5 and 1x10-6 M) showed that the O2 concentration decreased faster with increasing biofilm depth compared to the uranium free biofilms. In the uranium containing biofilms, the O2 consumption, calculated from the steady-state microprofiles, showed high consumption rates of up to 61.7 nmol cm-3 s-1 in the top layer (0–70 µm) and much lower consumption rates in the lower zone of the biofilms. Staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI) confirmed the high respiratory activities of the bacteria in the upper layer by confocal laser fluorescence microscopy (CLSM). The fast decrease in the oxygen concentrations in the biofilm profiles showed that the bacteria in the top region of the biofilms, i.e., the metabolically most active biofilm zone, battle the toxic effects of aqueous uranium with an increased respiratory activity. This increased respiratory activity results in O2 depleted zones closer to the biofilm/air interface which may trigger uranium redox processes, since suitable redox partners, e.g., extracellular polymeric substance (EPS) and other organics (e.g., metabolites), are sufficiently available in the biofilm porewaters. Such redox reactions may lead to precipitation of uranium (IV) solids and consequently to a removal of uranium from the aqueous phase.
Keywords: biofilm, uranium microscopy, microsensor
  • Poster
    IP FUNMIG Final Workshop, 24.-27.11.2008, Karlsruhe, Germany

Publ.-Id: 11929 - Permalink