Uranium as a stress factor in well aerated multispecies biofilms – A microsensor study of the O2 concentrations

Multispecies biofilms were cultured on glass slides in a standard culture medium (Sifin; TN 117) under air atmosphere in annular rotating reactors [1] for two months to obtain a thickness of approximately 800 µm. The slides with the grown biofilms were removed from one reactor for microsensor studies in a flow cell. Two other reactors were fed with UO2(ClO4)2 to adjust the total uranium concentration in the culture medium to 1x10-5 mol/l and 1x10-6 mol/l, respectively, i.e. the biofilms in these reactors were exposed to uranium for three weeks before they were removed for additional microsensor studies. Concentration profiles of oxygen versus biofilm depths were measured in each biofilm by electrochemical microsensors with a tip diameter of 10µm. A motor-driven micromanipulator was used for moving downwards through the biofilm in 20 or 50µm steps. The microsensor results clearly showed a significant dependence of the O2 concentration on the presence as well as on the concentration of uranium. In the absence of uranium the O2 concentration in the well aerated biofilm decreased slightly due to the aerophile microbes, dominating this biofilm. In contrast, O2 concentrations in the biofilms, which were exposed to different concentrations of uranium, decreased with increasing uranium concentration. Apparently, uranium acted as a stress factor for the microbes. Since metals have a strong effect on oxygen consumption, decreases in oxygen concentration could be due to changes in microbial activities [2] as well as on the activation of microbial communities induced by the addition of uranium [3]. 16S rDNA gene sequence retrieval and FISH are currently in progress to provide information on the changes occurring in the biofilm community and the resulting influence on the O2 concentration profiles.

[1] Lawrence, J. R. et al., (2000) Journal of Microbiological Methods 42, 215-224.
[2] Viret, H. et al., (2006) Sci Total Environ. 367, 302-311.
[3] Geissler, A. et al., (2005) Geobiology 3, 275-285.