Uranium Mining Wastes as a Reservoir of Unusual Bacteria Prospective for Bioremediation and Nanotechnology

Bacterial communities were studied in several uranium mining waste piles in Germany and in the USA by using 16S rDNA and RISA retrievals. Both approaches revealed extremely high and site-specific bacterial diversity. However, several bacterial groups including also novel lineages seem to be characteristic for the studied heavy-metal-polluted environments.
In parallel with the above mentioned direct molecular approaches, the method of enrichment culturing was applied in order to recover and study particular bacterial strains indigenous for the U wastes. Bacterial isolates belonging to different species representing diverse bacterial groups were recovered and characterized. The resistance and the interactions of these isolates with U and other heavy metals were demonstrated to be species- and even strain-specific. The atomic structures and the cellular location of the complexes formed by the isolates with U(VI) were studied using EXAFS spectroscopy, TEM, and EDX analyses. In all cases phosphate groups were predominantly implicated in the complexation of uranium but the structural parameters and the cellular location of the complexes differed between the studied bacterial groups.
Many of the studied strains possess unusual characteristics as the isolate JG-A12, for instance, which accumulates selectively U, Cu, Pb, Al, and Cd. This strain as well as it's intrinsic S-layer are forming U(VI)-complexes with identical structural parameters in which phosphorous residues in addition to the carboxyl groups are involved. ICP-MS and the "Stain-all" dye methods demonstrated that the S-layer of JG-A12 is phosphorylated. This can explain it's high ability to complex uranium and other metals. The latter seems to give an advantage to the strain to survive in the heavily polluted with uranium and other toxic metals environment from which it was recovered. Pd and Pt metallic nanoclusters were also successfully grown on the sheets of this S-layer. The latter is of interest for the nanotechnology. Interestingly, the S-layer of JG-A12 possesses unusual primary structure which indicates that lateral transfer was involved in the evolution of it's gene.
1848 words.
Keywords: bacterial diversity; S-layer, EXAFS, complexation of uranium