Complexation of uranium by three eco-types of Thiobacillus ferrooxidans

The complexation of uranium by the cells of the three recently described eco-types of T. ferrooxidans (Flemming et al., 1999; Selenska-Pobell et al., 1999) was studied. The uranium sorption studies showed that the strains from the three different types possess different capability to accumulate uranium. We have found that the representatives of type II accumulate significantly higher amounts of uranium in comparison to the other T. ferrooxidans strains studied. The amount of accumulated uranium gradually increased with increasing metal concentration at pH 1.5 and 4. The uranium tolerance investigations demonstrated that the types I and III are resistant to 8 and 9 mM of uranium respectively, whereas the type II does not tolerate more than 2 mM of uranium. Sodium carbonate was the most efficient desorbing agent tested, removing 97% of the uranium sorbed from the cells of T. ferrooxidans type III, and 88.33 and 88.50% from the cells of the types I and II, respectivley. Sodium citrate was the second best metal desorbing agent, whereas EDTA could remove only between 10 and 30% of the accumulated uranium. By the use of extended x-ray absorption fine structure (EXAFS) and infrared (IR) information was obtained about the exact chemical structure of the uranium complexes formed on the surface by the three eco-types of T. ferrooxidans.