Addition of U(VI) to a uranium mining waste sample and resulting changes in the indigenous bacterial community

Abstract

Based on 16S rRNA gene sequence retrieval, changes in natural bacterial community structure induced by addition of uranyl or sodium nitrate to soil samples from a uranium mining waste pile were investigated. Our results demonstrate that both treatments cause drastic changes in the bacterial composition of the studied samples, resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of particular denitrifying and nitrate‐reducing populations belonging to Actinobacteria and Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Instead, a strong propagation of Pseudomonas spp. from the Gammaproteobacteria occurred. At the initial stages of incubation (4 weeks after the addition of uranyl nitrate) U(VI)‐reducing Geobacter spp. appeared. However, at the later stages of incubation (14 weeks after the beginning of supplementation) no Geobacter populations were detected anymore. Interestingly, different U‐sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI)‐treated samples at these late stages of incubation. That indicated that the added U(VI) was no longer bioavailable. The drastic changes in bacterial community structure of the soil samples from the depleted uranium mining waste caused by the addition of uranyl nitrate indicate that most of the established indigenous bacterial populations do not tolerate U(VI). By the treatment with uranyl nitrate they are replaced by particular uranium resistant nitrate‐reducing and denitrifying populations that potentially interact with the added radionuclide. On the other hand, the large number of dead uranium‐sensitive bacteria likely liberates phosphate‐rich and other biopolymers capable of binding U(VI). On the basis of our results, we propose that bacteria along with the abiotic soil components such as minerals and humic acids may influence the behaviour of U(VI) in nature.

Geogenic Factors as Drivers of Microbial Community Diversity in Soils Overlying Polymetallic Deposits

“…In particular, Acidobacteria were commonly identified in soils and sediments overlying or containing U deposits, respectively, as well as in waste rock and mill tailings from U mines (36,54,56). In our study, many of the key organisms differentiating metal-rich from background sites matched probes of an Acidobacteria organism first identified by Geissler and Selenska-Pobell from U waste piles near Johanngeorgenstadt (Germany) (57). Other taxa first were identified in samples obtained from Au mines.…”

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

“…Oxidation of U(IV) at circumneutral pH under anaerobic conditions has been shown to occur during microbial nitrate reduction (denitrification) in the presence of Fe(III) and nitrate reducing organisms, including Geobacter, Arthrobacter, Klebsiella, and Thiobacillus species (Finneran et al, 2002;Beller, 2005;Geissler and Selenska-Pobell, 2005;Senko et al, 2005aSenko et al, , 2005bSuzuki and Suko, 2006). This process was not linked to cell growth and may proceed via an indirect pathway of reaction with intermediate products of denitrification (NO 2 À , NO, N 2 O).…”

Bacterial Diversity in Bentonites, Engineered Barrier for Deep Geological Disposal of Radioactive Wastes

“…The primers used for this reaction were the bacterial universal primers 16S8F (5'-AGAGTTTGATCCTGGCTCAG-3') [40] and 16S1492R (5'-TACGGYTACCTTGTTACGACTT-3') [41]. The PCR amplifications were performed as described by [42], using 2 µl of reaction mixture obtained combining three parallel replicates. A total of 100 single white colonies were randomly selected.…”

“…A total of 100 single white colonies were randomly selected. The inserted 16S rRNA gene fragments were amplified and further analyzed according to [42]. PCR products of selected clones were purified using Exo-SAP purification protocol, which uses two hydrolytic enzymes, Exonuclease I (New Englands Biolabs, U.K.)…”

“…After adding the enzymes to the PCR product a 30 min incubation at 37 °C is following and then an enzyme inactivation at 85 °C for further 15 min. Purified PCR products were sequenced as described by [42]. The rest of the clones, not grouped in any predominant type, were classified as individual representatives of the community.PCR products of these clones were sent to GATC Biotech (Germany) to be purified and sequenced.…”