Visualization of uranium in living biofilms in relation to biofilm structure and geochemical conditions


Visualization of uranium in living biofilms in relation to biofilm structure and geochemical conditions

Brockmann, S.; Großmann, K.; Krawczyk-Bärsch, E.; Arnold, T.; Wobus, A.

The speciation of uranium in environmentally relevant concentrations of 1×10-5 mol/l in biofilms was investigated by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach. The microbial communities in the biofilms were determined by analysis of the amplified 16S rRNA gene fragments. No changes of the microbiological diversity were observed in the biofilms in contact with uranium and without. The respiratory activity was microscopically investigated by staining experiments with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4,6-diamidino-2-phenylindole (DAPI). It was found that in the presence of uranium (1×10-5 mol/l added as UO2(ClO4)2) the biofilm responded with a higher respiratory activity of the bacteria in the upper layer, leading to changes of geochemical gradients within the biofilms with corresponding effects on the uranium geochemistry. These effects include a change in oxidation state and precipitation of respective uranium phases.
Laser fluorescence spectroscopy was used to identify in-situ and in a non-invasive fashion the speciation of uranium within the biofilms. A fluorescence signal in the wavelength range of 415-475 nm was indicative for metastable uranium- (V) and a fluorescence signal in the range of 480-560 nm was identified as uranium(VI), clearly showing that redox processes take place within the biofilms.
We found that aqueous uranium in environmentally relevant concentrations may trigger higher O2 consumption rates which lead to larger reducing zones within the biofilms. Consequently, such zones may be responsible for an increased immobilization of uranium from the surrounding bulk solution. Our studies indicated that the microbial influence on the migration behavior of uranium in the environment has to be included in performance assessment studies to predict more realistic uranium migration scenarios.

Keywords: Biofilm; uranium; metabolism; staining; CLSM

  • Poster
    Biofilm III, 3rd International Biofilms Conference, 06.-08.10.2008, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-11768
Publ.-Id: 11768