Bacterial diversity at abandoned uranium mining and milling sites in Bulgaria as revealed by 16s RRNA genetic diversity study

Radionuclide and heavy metal contamination influences the composition and diversity of bacterial communities, thus adversely affecting their ecological role in impacted environments. Bacterial communities from uranium and heavy metal-contaminated soil environments and mine waste piles were analyzed using 16S rRNA gene retrieval. A total of 498 clones were selected, and their 16S rDNA amplicons were analyzed by restriction fragment length polymorphism, which suggested a total of 220 different phylotypes. The phylogenetic analysis revealed Proteobacteria, Acidobacteria, and Bacteroidetes as the most common bacterial taxa for the three sites of interest. Around 20-30 % of the 16S rDNA sequences derived from soil environments were identified as Proteobacteria, which increased up to 76 % (mostly Gammaproteobacteria) in bacterial communities inhabiting the mine waste pile. Acidobacteria, known to be common soil inhabitants, dominated in less contaminated environments, while Bacteroidetes were more abundant in highly contaminated environments regardless of the type of substratum (soil or excavated gravel material). Some of the sequences affiliated with Verrucomicrobia, Actinobacteria, Chloroflexi, Planctomycetes, and Candidate division OP10 were site specific. The relationship between the level of contamination and the rate of bacterial diversity was not linear; however, the bacterial diversity was generally higher in soil environments than in the mine waste pile. It was concluded that the diversity of the bacterial communities sampled was influenced by both the degree of uranium and heavy metal contamination and the site-specific conditions. © 2013 Springer Science+Business Media Dordrecht.