Changes in microbial community structure induced by addition of U(VI) to uranium mining waste samples

Microorganisms are involved in biogeochemical transformations and migration of uranium in the environment. In order to study the influence of U(VI) on natural bacterial and archaeal communities, a soil sample collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt was treated with different amounts of uranyl or sodium nitrate as a control. The samples were incubated for different periods of time and at different aeration conditions and their microbial communities were analyzed by the 16S rDNA retrieval using bacteria- and archaea-specific primers. Bacterial community of the untreated sample was predominated by Alphaproteobacteria and Acidobacteria. The increasing of the uranium content up to 100 mg U/kg with a subsequent incubation for four weeks under aerobic conditions stimulated a propagation of Pseudomonas spp., Arthrobacter spp. and Geobacter spp. Treatment of a parallel sample with sodium nitrate under the same conditions induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. After a longer incubation of fourteen weeks even in most contaminated samples containing 300 mg U/kg U-sensitive Bacteroidetes and alphaproteobacterial populations were stimulated. In parallel samples incubated under anaerobic conditions mainly Betaproteobacteria were identified. Archaeal diversity of the uranyl and sodium nitrate treated samples was significantly lower than in untreated samples and only sequences related to Crenarchaeotea were found. Our results demonstrate for the first time changes in the structure of a natural microbial community induced by incubation with uranyl nitrate for different periods of time and at different aeration conditions.