Influence of U(VI) on natural bacterial community of a soil sample from a uranium mining waste

Bacteria have evolved several different mechanisms to tolerate uranium or to use U(VI) as terminal electron acceptor in anaerobic respiration. Because of this, bacteria play a major role in geomicrobiological cycling of uranium and can be used for the bioremediation of uranium-contaminated sites. In this work natural bacterial communities were investigated by the use of 16S rDNA retrievals in several soil samples from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). Inductively coupled plasma mass spectrometry (ICP-MS) and selective sequential extraction (SSE) analysis were used for the geochemical characterization of the soil samples. The 16S rDNA analysis showed that the natural bacterial communities were predominated by -Proteobacteria and Acidobacteria. SSE analysis demonstrated that the uranium was weakly complexed and bound by Mn(hydr)oxides or Fe(hydr)oxides. The soil samples contain in addition to uranium also other heavy metals like arsenic for example. In order to understand how U(VI) influences the structure of natural bacterial community, one of the studied samples with the lowest indigenous amount of U was supplemented with 60 mg/kg U(VI) in form of uranyl nitrate. After four weeks of incubation, SSE analysis and 16S rDNA retrieval were done in parallel. The SSE analysis demonstrated that most of the supplemented uranium was weakly complexed and remained probably bioavailable. The 16S rDNA retrieval showed that populations of Pseudomonas, Arthrobacter and Geobacter were stimulated by the addition of U(VI) to the soil sample. For more profound understanding of the influence of U(VI) on natural bacterial community, column experiments are running in our laboratory.