Bacterial Diversity and Activity in Uranium Waste Piles

Bacterial diversity in subsurface soil samples drawn from different depths of several uranium waste piles was studied using the 16S rDNA retrieval. Extremely high diversity was found in all samples investigated. In particular, the presence of several dominant 16S rDNA groups related to the genara $\I Thiobacillus, Bacillus, Pseudomonas, Desulfovibrio $$END was demonstrated. One of these 16S rDNA groups was affiliated to the species $\IT. ferrooxidans$$END. Interestingly, this group includes three 16S rDNA types which possess slightly different sequences. Strains of $\IT. ferrooxidans$$END corresponding to two of the mentioned three 16S rDNA types were recovered from two soil samples polluted in different extend with heavy metals. The two groups of isolates have different genomic organization. In addition, the members of the group recovered from the more polluted sample are tollerant to higher concentrations of uranyl ions which are lethal for the isolates of the second group. The expression of at least three genes of the U-tolerant strains is influenced by by the presence of uranyl ions in the nutrient medium. The capability of the U-mine isolates to interact with U(VI) was studied, and it was found that they accumulate significantly higher amounts of U(VI) in comparison to several reference $\IT. ferrooxidans$$END strains recovered from other environments. Using time-resolved laser fluorescence spectroscopy it was shown that the complexes build by one of the U-waste isolates with U(VI) are much stronger than those build by the reference strains. This is the first report which demonstrates a microdiversity in closely related natural isolates of $\IT. ferrooxidans$$END. We suggest that the microdiversity obsrved reflects the genetic adaptation of the strains studied to the different heavy metal concentrations in their natural environments.