Uranium contaminated environments as a reservoir of unusual bacteria prospective for bioremediation and nanotechnology

Microbial communities were studied in several uranium mining wastes in Germany and in the USA by using the rDNA retrieval applying several sets of amplification primers flanking different regions of the rrn operons (1, 2). The bacterial populations in the studied soil samples were rather dense and extremely diverse. In the water samples a lower grade of bacterial diversity was found. Despite the fact that the composition of the bacterial communities was site-specific, several bacterial groups including also novel lineages seem to be characteristic for the studied heavy-metal-polluted environments. The archaeal populations, in contrast, were not very dense and were limited to several not yet cultured Crenarchaeotae lineages which were identified in other metal contaminated environments as well.
In parallel to the above mentioned direct molecular approach, 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 (1). The resistance and the interactions of these isolates with U and with other heavy metals were demonstrated to be species- and even strain-specific. The atomic structures and the cellular location of the complexes formed with U(VI) by the isolates 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 (3).
Many of the studied strains possess unusual characteristics as the isolate JG-A12, for instance, which accumulates selectively U, Cu, Pb, Al, and Cd (4). This strain as well as its 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 demonstrated that the S-layer of JG-A12 is phosphorylated. This can explain its high ability to complex uranium and other metals. The latter seems to give an advantage to the strain to survive in environments heavily polluted with uranium and other toxic metals from which it was recovered.
Sol-gel ceramics with high and reversible metal binding capacity were prepared via homogeneous dispersion and embedding of B. sphaericus JG-A12 vegetative cells (5, 6). This biological ceramics are very perspective for bioremediation of heavy metal contaminated water wastes.
In addition, Pd nanoclusters were also successfully grown on the surface of these bacteria. The latter is of interest for the nanotechnology. Interestingly, the above mentioned S-layer of JG-A12 possesses an unusual primary structure which indicates that lateral transfer was involved in the evolution of its gene.
References
1. Selenska-Pobell, S. (2002) Interactions of Microorganisms with Radionuclides p. 225-253; Elsevier, Oxford
2. Selenska-Pobell, S., et al. (2001) Antonie van Leeuwenhoek 79, 149-161.
3. Merroun M. et al. (2003) FZR-Report No. 364, p. 26-30
4. Selenska-Pobell, S. et al. (1999) FEMS Microbiol. Ecol. 29, 59-67
5. Raff, J. et al. (2003) Chem. Mater. 15 (1): 240-244.
6. Soltmann et al. (2003) J Sol-Gel Science and Technology 26, 1209-1212.