Bacterial diversity and activity in Uranium waste piles

Bacterial diversity in soil samples drawn from different depths of several uranium waste piles was studied using 16S rDNA retrieval, RISA and rep-APD. Extremely high diversity was found in all samples investigated. Several dominant 16S rDNA groups related to the genera Thiobacillus, Bacillus, Pseudomonas, and Desulfovibrio were demonstrated. One of these groups was affiliated to the species T. ferrooxidans. This group includes three 16S rDNA types with slightly different sequences. Strains of T. ferrooxidans corresponding to two of the mentioned three 16S rDNA types were recovered from two samples of the waste polluted in different extend with heavy metals. The interactions of the natural T. ferrooxidans strains with U(VI) were group-specific. Microdiversity at the level of 16S- and IGS-rDNA was found also among the group of the uranium reducing Desulfovibrio waste isolates. The latter were affiliated to Desulfovibrio vulgaris subspecies oxamicus. These natural isolates are able to reduce more effectively higher amounts of U(VI) than the reference Desulfovibrio strains. In contrast to the reference strains, the waste isolates reduce U(VI) to U(IV) independently of the pH range of the medium. This is the first report demonstrating microdiversity of closely related natural isolates of T. ferrooxidans and D. vulgaris subsp. oxamicus. We suggest that the microdiversity observed reflects the genetic adaptation of the strains studied to the different heavy metal concentrations in their natural environments.