Molecular analysis of bacterial communities in uranium polluted waste piles

Bacterial diversity was studied in soil and water samples drawn from different sites and depths of several uranium mining waste piles, mill-tailings and disposal sites by the use of 16S rDNA and RISA retrievals. These studies demonstrated significant differences in the structure of the natural communities and in the degree of bacterial variability between the environments studied. The predominant bacterial groups in the samples analysed were in general site-specific. However, many samples share common bacterial groups, belonging mainly to the g subgroup of Pseudomonas; to the sulfate and metal reducing genera such as Desulfovibrio and Geobacter (d-Proteobacteria); to the Gram-positive bacteria with a low DNA G+C content (Bacillus/Clostridium); to the aerobic chemolithoautotrophs oxidising iron and/or sulfur compounds (Acidithiobacillus); or to those oxidising nitrite (Nitrospina) and ammonium (Nitrosomonas) b-Proteobacteria. Interestingly, 16S rDNA sequences indicating the presence of the recently discovered anaerobic chemolithotrophic ammonium oxidising bacteria named Anammox were found to be ubiquitous in many of the uranium waste samples studied [1]. The Anammox was identified as a novel autotrophic member of the order Planctomycetales, one of the major distinct divisions of Bacteria [2].
In all three kinds of uranium polluted wastes the presence of a large variety of not yet cultured representatives belonging to Holophaga/Acidomicrobium and Cytophaga/Flexibacter clusters was also shown. In addition, many 16S rDNA sequences were affiliated with various undefined so called "candidate" bacterial divisions.

In parallel to the above described culture independent approach, the classical method of enrichment culturing was applied to analyse the bacteria present in the uranium polluted environments. The aim was to culture and study particular bacterial groups which are of interest because of their ability to biotransform heavy metals and radionuclides.
Among the cultured bacterial strains predominant were those belonging to the genera Acidithiobacillus, Agrobacterium, Bacillus, Desulfovibrio, Desulfotomaculum, Leptospirillum, Pseudomonas, Rhizobium, and Stenotrophomonas. Many of the strains cultured are representing novel species within the above mentioned genera.
These natural bacterial isolates are prospective for in situ bioremediation of the uranium mining wastes piles, because they are well adapted to the extremely complex conditions in those heavily polluted environments.

References:

[1] Radeva, G., et al., (1999) Annual Report FZR 285, 56
[2].