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To assess the safety of a radioactive waste repository it is crucial to understand the transport of radionuclides in the environment. It is worldwide consensus that the waste should be stored in a deep geological repository to isolate it from the biosphere. Besides rock salt and clay rock, in several countries, e.g. Germany, crystalline rock is considered a potential host rock. There, alumosilicates represent key mineralogical components. Retention of trivalent actinides through sorption onto these minerals has been documented in the literature. However, differences in mineral solubility can influence their surface chemistry. Dissolved Al3+ is of particular importance due to its potential to re-adsorb onto mineral surfaces. Previous studies have indicated that aqueous aluminum species affect the sorption behavior of trivalent actinides and lanthanides on K-feldspars.[1] Even surface precipitates were formed during interaction of Al3+ and mica.[2] Nevertheless, the fundamental mechanisms remain incompletely understood, partly due to the inherent challenge of detecting alterations in Al3+ surface concentration in the presence of aluminosilicate minerals. In this study, hematite (Fe2O3) serves as an aluminum-free model system to investigate the influence of Al3+ on mineral surfaces in more detail. We anticipate competitive reactions with actinides during sorption to rock surfaces, and our goal is to gain a deeper understanding of these processes and their influence on actinide retention. First experiments regarding the sorption of Al3+ on hematite revealed a sorption edge at a pH value of ~4 (100 µM Al3+, 0.01 M NaCl, S/L = 3 g/L). Simultaneous solubility investigations exclude the potential impact of bulk precipitation of Al3+ on the sorption edge. Zeta potential measurements yield an isoelectric point for hematite at a pH value of ~8, i.e. Al3+ sorption occurs on a positively charged surface. Further insights into these processes will be gained by transmission electr

The stored data sets represent both the raw data and the evaluated data that were used for the publication about speciation-dependent uranium(VI) reduction by an iron-reducing bacteria in both pure culture and artificial multispecies bio-aggregates.

High-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy was used to investigate the reduction of U(VI) by the sulfate-reducing bacterium Desulfosporosinus hippei DSM 8344T, confirming the partial reduction of U(VI) and the presence of U(V).

I. EINLEITUNG Für eine umfassende Sicherheitsbewertung der geologi-schen Tiefenlagerung hochradioaktiver Abfälle müssen verschiedene Aspekte berücksichtigt werden. Neben den geologischen, geochemischen und geophysikalischen Eigen-schaften spielt der Einfluss von natürlich vorkommenden Mikroorganismen im umgebenden Wirtsgestein und im Verfüllmaterial eine entscheidende Rolle in der Umgebung eines solchen Endlagers. Tongesteine sind potenzielle Wirts-gesteine für die Endlagerung dieser Abfälle, während Ben-tonite als Verfüllmaterial nicht nur für ein Endlager in Ton-gesteinen, sondern auch in kristallinen Gesteinen vorgesehen sind. Wenn im ungünstigsten Fall Wasser in das Endlager eindringt, können Radionuklide aus den Abfallbehältern austreten und mit den Mikroorganismen interagieren. Dies kann z. B. zu Veränderungen der chemischen Speziation oder des Oxidationszustandes der Metallionen führen. II. ERGEBNISSE UND DISKUSSION Unter endlagerrelevanten Bedingungen stellen Desul-fosporosinus spp. wichtige Vertreter der sulfatreduzierenden anaeroben Bakterien dar, welche sowohl in Tonformatio-nen als auch im Verfüllmaterial Bentonit vorkommen (Bagnoud et al. 2016, Matschiavelli et al. 2019). Verschie-dene Studien zeigen, dass sie eine wichtige Rolle in den mik-robiellen Gemeinschaften dieser Umgebung spielen. Ein mit den isolierten Arten eng verwandter Mikroorganismus ist Desulfosporosinus hippei DSM 8344T (Vatsurina et al. 2008). Daher wurde dieses Bakterium ausgewählt, um des-sen Wechselwirkungen mit Uran(VI) zu untersuchen, insbe-sondere im Hinblick auf die Reduktion zum weniger mobi-len Uran(IV), welches günstige Eigenschaften wie eine gerin-gere Mobilität aufweist und damit eine verbesserte Rückhal-tung des Radionuklids im Wirtgestein ermöglicht wird. Zeitabhängige Reduktionsexperimente in künstlichem Opalinuston-Porenwasser (Wersin et al. 2011) mit einer Uran(VI)-Konzentration von 100 µM bei einem pH von 5.5 zeigten eine Abnahme der Uran(VI)-Konzentrationen von ca. 8

Die sichere Entsorgung hochradioaktiver Abfälle stellt eine wichtige wissenschaftli-che und gesellschaftliche Herausforderung dar. Tongesteine sind potentielle Wirts-gesteine für die Endlagerung dieser Abfälle in einem geologischen Tiefenlager. Ben-tonite sollen dabei als Verfüllmaterial nicht nur für ein Endlager in Tonformationen, sondern auch in kristallinem Gestein dienen. Für eine langfristige Sicherheitsbewer-tung müssen verschiedene Aspekte berücksichtigt werden. Neben geologischen, ge-ochemischen und geophysikalischen Gesichtspunkten spielen auch natürlich vor-kommende Mikroorganismen eine entscheidende Rolle in der Umgebung eines sol-chen Endlagers. Gelangt in einem Worst-Case-Szenario Wasser in das Endlager, können diese mit den freigesetzten Radionukliden wechselwirken und beispielswei-se die chemische Speziation oder den Oxidationszustand verändern. In dieser Arbeit wurden die Wechselwirkungen des anaeroben, sulfatreduzierenden Bakteriums Desulfosporosinus hippei DSM 8344T, einem Vertreter der Gattung Desul-fosporosinus, die in Tongestein und Bentonit vorkommt, mit Uran(VI) und Europi-um(III) mit Hilfe verschiedener mikroskopischer, spektroskopischer und molekular-biologischer Methoden untersucht. Die Ergebnisse lieferten einen umfassenden Einblick in die ablaufenden Wechselwirkungsprozesse und zeigten deutliche Unter-schiede zwischen den untersuchten Elementen auf. Im Zuge dessen wurde ein be-sonderes Augenmerk auf die Untersuchung der Reduktion von Uran(VI) durch D. hippei DSM 8344T gelegt. Für dieses Element konnte eine Immobilisierung in einem gekoppelten Assoziations-Reduktionsmechanismus nachgewiesen werden. Im Ge-gensatz dazu wechselwirkte nur ein geringer Anteil des gelösten Europium(III) mit den Zellen des anaeroben Mikroorganismus, wobei eine teilweise Biopräzipitation von Europiumphosphat beobachtet werden konnte. Die Wechselwirkung des Mikroorganismus mit Uran(VI) wurde zunächst in einem Bikarbonat-gepufferten System untersucht, wobei keine A, The safe disposal of high-level radioactive waste is a major scientific and societal challenge. Clay rocks are potential host rocks for the final disposal of the nuclear waste in a deep geological repository. Bentonites should serve as backfill material for a repository not only in clay formations, but also in crystalline rocks. Various aspects have to be considered for a long-term safety assessment. In addition to geological, geochemical and geophysical aspects, naturally occurring microorganisms in the en-vironment of such a repository play a decisive role. In the event of a worst-case sce-nario, if water enters the repository, these microorganisms can interact with the re-leased radionuclides and, for example, change the chemical speciation or oxidation state. In this work, the interactions of the anaerobic sulfate-reducing bacterium Desul-fosporosinus hippei DSM 8344T, a member of the genus Desulfosporosinus, which can be found in clay rock and bentonite, with uranium(VI) and europium(III) were in-vestigated using various microscopic, spectroscopic and molecular biological meth-ods. The results provided a comprehensive insight into the interaction processes and revealed significant differences between the investigated elements. Special attention was paid to the reduction of uranium(VI) by D. hippei DSM 8344T. For this element, an immobilization in a coupled association-reduction mechanism was demonstrated. In contrast, only a small fraction of the dissolved europium(III) interacted with the cells of the anaerobic microorganism, and a partial bioprecipitation of europium phosphate was observed. The interaction of the microorganism with uranium(VI) was first investigated in a bicarbonate-buffered system, where no decrease in uranium concentrations was observed, and thus probably no reduction of uranium(VI) occurs. In addition, ex-periments in synthetic Opalinus Clay pore solution were carried out. The investiga-tions with two different initial uranium(VI) concentr

Redox transformations have a strong influence on the mobility of different metal ions in the environment. A key process in influencing the migration of uranium is the reduction of highly mobile and water-soluble uranium(VI) to less mobile uranium(IV). Especially in the surroundings of former uranium mines, this radionuclide represents an important contaminant whose entry into the environment must be prevented. Different microorganisms, e.g. sulfate- and iron-reducing bacteria, are capable of reducing uranium under various conditions. Thus, microbes can offer an environmentally friendly remediation strategy for radionuclide-contaminated environments. Moreover, in this study, we introduce the use of artificial bio-aggregates of different bacterial genera as a potential bioremediation approach combining advantageous properties of the microorganisms in a complementary way. Desulfitobacterium sp. G1-2, which was isolated from bentonite samples, was chosen as an important representative of iron-reducing bacteria in anaerobic environments. Furthermore, different Desulfitobacterium species were found in other natural environments, like clay formations as well. These bacteria were used to form artificial bio-aggregates with different other bacterial strains (e.g. aerobic marine inhabitant Cobetia marina DSM 50416) based on electrostatic modifications of the surface charge of the bacterial cells. Time-dependent experiments of a pure Desulfitobacterium sp. G1-2 culture in 30 mM bicarbonate buffer as background electrolyte showed a decrease in uranium concentration in the supernatants (100 µM uranium(VI), 10 mM lactate, pH 6.8/5.5). Approximately 80% of the uranium were removed from the supernatants within one week. UV/Vis studies of the dissolved cell pellets verified the reduction of uranium(VI) in the samples. STEM imaging of ultra-thin sectioned samples of uranium-incubated cells coupled with EDX spectroscopy showed the presence of two different uranium-containing aggregate

The reduction of highly mobile and water soluble U(VI) to less mobile U(IV) represents a key process influencing the migration of this radionuclide in the environment. Microorganisms such as for example iron and sulfate-reducers are capable of reducing U(VI) under various conditions. This interaction mechanism between microbes and U could play an important role in a final disposal site for high-level radioactive waste deposited in deep geological layers. Different host rocks are suitable for the long-term storage of nuclear waste, e.g. clay formations, crystalline rock and rock salt. Besides the geochemical, geophysical and geological properties of such a repository, little is known about the influence of naturally occurring microorganism on the safety of such a site. In a worst-case scenario, if water enters the repository, radionuclides can get distributed in the surrounding host rock and thus interact with the native microorganisms, potentially leading to an immobilization of radionuclides via bioreduction. Furthermore, a reduction of U(VI) could also play an important role in the development of different bioremediation approaches for radionuclide-contaminated environments. As a potential component of new remediation strategies, we introduce the use of artificial bio-aggregates of different bacterial genera. By the use of these artificial biofilms insights into the complex interactions in a multi-species environment can be obtained. In this study, we used derivatized polyelectrolytes to form aggregates of two different microorganisms to connect advantageous properties of the microorganisms in a complementary way and to investigate the reduction of U(VI) under different conditions. Desulfitobacterium sp. G1-2 was chosen as an important representative of iron-reducing bacteria in anaerobic environments. This bacterial strain was isolated from bentonite samples of the Full-scale Engineered Barrier Experiment – Dismantling Project (FEBEX-DP) at the Helmholtz Center D

The safe disposal of high-level radioactive waste represents a major scientific and societal challenge. In addition to geological, geochemical and geophysical properties of such a repository, the influence of naturally occurring microorganisms from deep geological layers has to be taken into account for a comprehensive safeguard concept. Various sulfate- and iron-reducing bacteria are present in different clay formations, which can serve as a potential host rock for the long-term storage of the waste, as well as in the backfill material bentonite. In the event of a worst-case scenario, if water enters the repository, those microorganisms can interact with the waste and change for example the oxidation state or the chemical speciation, which can influence the mobility of the radionuclides. In this study, the reduction of highly-mobile, water-soluble U(VI) to less mobile U(IV) by the iron-reducing microorganism Desulfitobacterium sp. G1-2 and the sulfate-reducer Desulfosporosinus hippei DSM 8344T were investigated. Desulfitobacterium sp. G1-2 has been isolated from a bentonite sample and Desulfosporosinus hippei DSM 8344T represents a genus of sulfate-reducing bacteria present in clay rock and bentonite. During time-dependent experiments in bicarbonate buffer (30 mM, 100/550 µM U(VI)), Desulfitobacterium sp. G1-2 showed a removal of up to 80% of U within 5 days, whereas samples of Desulfosporosinus hippei DSM 8344T showed no decrease in U concentrations over time. Therefore, experiments were carried out in artificial Opalinus Clay pore water with this bacterium (100 µM U(VI), pH 5.5). In this case, the U concentration showed a decrease of up to 80% of the radionuclide from the supernatants within 48 h. UV/Vis studies of dissolved cell pellets of both bacteria after U incubation showed an almost complete reduction to U(IV) for Desulfitobacterium sp. G1-2. On the other hand, samples of Desulfosporosinus hippei DSM 8344T exhibited only a partial reduction. TEM imaging co

The microbial reduction of U(VI) to U(IV) can decrease the mobility of U contaminants in the environment and may have a significant impact on the safety of a nuclear waste repository, as well as, the potential to serve as a component in bioremediation strategies for U-contaminated environments. In this study, we show significant differences in the reduction mechanisms for iron- and sulfate-reducing bacteria, highlighting the importance of investigating microbe-uranium interaction of different bacterial genera. Moreover, we introduce the use of artificial bio-constructs to study U reduction by microbial communities to gain insights into the complex interactions in a multi-species environment. To gain molecular process understanding regarding microbial U reduction Desulfosporosinus and Desulfitobacterium spp. were chosen as important representatives of sulfate- and iron-reducing bacteria in anaerobic environments. Furthermore, their U reduction capabilities were investigated using artificial bio-constructs with different other microbial species. Time-dependent experiments of pure cultures in bicarbonate buffer (30 mM, 100 µM U(VI), 10 mM lactate) showed a decrease of U concentrations in the supernatant of Desulfitobacterium sp. G1-2, whereas no changes occurred for Desulfosporosinus hippei DSM 8344T. In contrast, in artificial Opalinus Clay pore water (100 µM U(VI), pH 5.5, 10 mM lactate) up to 80% of the radionuclide got removed by both microorganisms. UV/Vis studies verified the reduction of U(VI) to U(IV) in the cell pellets. STEM-EDXX revealed the presence of two different U-containing aggregates inside the cells of Desulfitobacterium sp. G1-2, while cells of Desulfosporosinus hippei DSM 8344T showed almost no U uptake but U-aggregates on the cell surface. First experiments with artificial bio-constructs that were formed from different bacterial genera using polyelectrolyte-controlled aggregation showed a promising U reduction capacity. Such artificial biostructur

Microbial U(VI) reduction influences the uranium mobility in contaminated subsurface environments and can affect the disposal of high-level radioactive waste by transform-ing the water-soluble U(VI) to less mobile U(IV). The reduction of U(VI) by the sulfate-reducing bacterium Desulfosporosinus hippei DSM 8344T, a close phylogenetic relative to naturally occurring microorganism present in clay rock and bentonite, was investigat-ed. D. hippei DSM 8344T showed a relatively fast removal of uranium from the superna-tants in artificial Opalinus Clay pore water. Combined speciation calculations and lumi-nescence spectroscopic investigations showed the dependence of U(VI) reduction on the initial U(VI) species. Scanning transmission electron microscopy coupled with ener-gy-dispersive X-ray spectroscopy showed uranium-containing aggregates on the cell surface and the formation of membrane vesicles. By combining different spectroscopic techniques, including UV/Vis spectroscopy, as well as uranium M4-edge X-ray absorp-tion near-edge structure (XANES) recorded in high-energy-resolution fluorescence-detection (HERFD) mode and extended X-ray absorption fine structure (EXAFS) analy-sis, the partial reduction of U(VI) could be verified, whereby the formed U(IV) product has an unknown structure. Furthermore, the U M4 HERFD-XANES showed the presence of U(V) during the process, suggesting a single-electron transfer mechanism for the microbial U(VI) reduction by sulfate reducers. These findings offer new insights into the U(VI) reduction by sulfate-reducing bacteria and contribute to a comprehensive safety concept for a repository for high-level radioactive waste.

The aim of the lecture is to give an overview of the equipment at the Institute of Resource Ecology and what analytical options this includes. Furthermore, current research work is presented in the context of the remediation of contaminated water and soil. Building on this, the potential and limits of biological processes and possibilities for collaboration will be shown.

Micro- and nanoplastics are emerging pollutants with a concerning persistence in the environment. Research into their environmental impact requires addressing challenges related to sensitively and selectively detecting them in complex ecological media. One solution with great potential for alleviating these issues is using radiolabeling strategies. Here, we report the successful introduction of a 64Cu radiotracer into common microplastics, namely polyethylene, polyethylene terephthalate, polystyrene, polyamide, and polyvinylidene dichloride, which allows the sensitive detection of mere nanograms of substance. Utilizing a Hansen Solubility Parameter screening, we developed a swelling and in-diffusion process for tetraphenylporphyrin-complexed 64Cu, which permits one-pot labeling of polymer particles

Microorganisms show a high affinity for trivalent actinides and lanthanides, which play an important role in the safe disposal of high-level radioactive waste as well as in the mining of various rare earth elements. The interaction of the lanthanide Eu(III) with the sulfate-reducing microorganism Desulfosporosinus hippei DSM 8344T, a representative of the genus Desulfosporosinus that naturally occurs in clay rock and bentonite, was in-vestigated. Eu(III) is often used as a non-radioactive analogue for the trivalent actinides Pu(III), Am(III), and Cm(III), which contribute to a major part of the radiotoxicity of the nuclear waste. D. hippei DSM 8344T showed a weak interaction with Eu(III), most likely due to a complexation with lactate in artificial Opalinus Clay pore water. Hence, a low removal of the lanthanide from the supernatant was observed. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy revealed a bioprecipitation of Eu(III) with phosphates potentially excreted from the cells. This demonstrates that the ongoing interaction mechanisms are more complex than a sim-ple biosorption process. The bioprecipitation was also verified by luminescence spec-troscopy, which showed that the formation of the Eu(III) phosphate compounds starts almost immediately after the addition of the cells. Moreover, chemical microscopy pro-vided information on the local distribution of the different Eu(III) species in the formed cell aggregates. These results provide first insights into the interaction mechanisms of Eu(III) with sulfate-reducing bacteria and contribute to a comprehensive safety concept for a high-level radioactive waste repository, as well as to a better understanding of the fate of heavy metals (especially rare earth elements) in the environment.

The stored data sets represent both the raw data and the evaluated data that were used for the publication about interactions of a sulfate-reducing bacterium with europium(III).

Daten zur Radiomarkierung von Mikroplastikpartikeln: Cu-Komplexierung; Cu-64 eindiffusion, Fluoreszenz-Markierung; HSP screening; Hydrophobizitäts Messungen; Elektronen-/Lichtmikroskopie; Quellversuche; Spektren.

For a comprehensive safety assessment of a nuclear repository, the influence of naturally occurring microorganisms from deep geological layers has to be taken into account. Clay rock represents a suitable host rock for the long-term storage of high-level radioactive waste with bentonite as backfill material. In the event of a worst-case scenario, water can enter the repository, solubilize components of the waste, and transport it into the surrounding barriers. In this case, microorganisms can interact with the radionuclides and thereby change the chemical speciation or induce redox reactions. Desulfosporosinus species represent important members of anaerobic, sulfate-reducing bacteria present in both, clay rock and bentonite. They occur, among others, in the pore water of Opalinus Clay and in the Bavarian bentonite B25. [1,2] Desulfosporosinus hippei DSM 8344T is a close phylogenetic relative to an isolated bacterium from bentonite samples. [3] Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions, especially regarding the reduction to the less mobile uranium(IV). Artificial Opalinus Clay pore water [4] served as background electrolyte for the reduction experiments (100 µM uranium(VI), pH 5.5), in which the uranium concentrations in the supernatants decreased rapidly. Time-resolved laser-induced fluorescence spectroscopy showed the presence of a uranyl lactate and a uranyl carbonate complex as aqueous species in the supernatant. While the proportion of the uranyl lactate complex decreased with the incubation time, the uranyl carbonate fraction remained almost constant. UV/Vis studies of the dissolved cell pellets provided clear proof of a partial reduction of uranium(VI) to uranium(IV) of up to 39% in the samples. Therefore, a combined association-reduction process is a possible interaction mechanism. TEM images showed the presence of uranium-containing aggregates on the cell surface. To mitigate encrustation, cells rel

INTRODUCTION For a comprehensive safety assessment regarding the deep geological disposal of high-level radioactive waste, various aspects have to be taken into account. Besides geological, geochemical, and geophysical properties, the influence of naturally occurring microorganisms in the surrounding host rock and backfill material play a crucial role in the environment of such a repository. Clay formations are potential host rocks for the long-term storage of this waste, whereas bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. In the event of a worst-case scenario, if water enters the disposal site, radionuclides can escape from the waste canisters and thus interact with the microorganisms. This can, for example, lead to changes in the chemical speciation or the oxidation state of the metal ions. RESULTS & DISCUSSION Under repository-relevant conditions, Desulfosporosinus spp. are important representatives of anaerobic, sulfate-reducing bacteria being present in clay formations as well as in bentonites. Various studies show that they are playing a major role in the microbial communities of these surroundings. A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344T. Therefore, this bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less-mobile uranium(IV) having favorable properties like a reduced mobility. Time-dependent reduction experiments showed the removal of about 80% of the uranium(VI) from the supernatants in artificial Opalinus Clay pore water (100 µM uranium(VI), pH 5.5) within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets provide clear proof of the formed uranium(IV). The proportion of this oxidation state in the cell-bound uranium increases up to 40% after one week. Therefore, a combined sorption-reduction process is a possible interaction mechan

Clay rock represents a suitable host rock for the long-term storage of high-level radioactive waste with bentonite as backfill material. In the event of a worst-case scenario, water can enter the repository. It is possible that naturally occurring microorganisms can interact with the radionuclides and thereby change the chemical speciation or induce redox reactions. Among different sulfate-reducing bacteria, Desulfosporosinus species represent important members of the microbial communities in both clay rock and bentonite.[1,2] Desulfosporosinus hippei DSM 8344T is a close phylogenetic relative to an isolated bacterium from bentonite.[3] Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers. Time-dependent experiments in artificial Opalinus Clay pore water[4] (100 µM uranium(VI), pH 5,5) showed a high removal of uranium from the supernatants within a short time range. UV/Vis studies of the dissolved cell pellets provided clear proof of a partial reduction of uranium(VI) to uranium(IV) in the samples, although bands of uranium(VI) were still observable. These findings propose a combined association-reduction process as an explanation for the ongoing interaction mechanism. Uranium aggregates formed on the cell surface were visible in TEM images. Furthermore, cells released membrane vesicles as a possible defense mechanism against cell encrustation. In addition, HERFD-XANES measurements confirmed the reduction of uranium(VI). But with these measurements also the presence of uranium(V) in the cell pellets could be demonstrated. This provides first evidence of the involvement of uranium(V) in uranium(VI) reduction by sulfate-reducing microorganisms. With the help of EXAFS measurements, different cell-related uranium species were detected. This study helps to better understand the complexity of redox processes in the environment and contribute to a safety conc

The safe disposal of high-level radioactive waste represents a significant scientific and societal challenge. According to geological, geochemical, and geophysical properties, clay formations represent a suitable host rock for the long-term storage of this waste. However, for a comprehensive safety assessment, the influence of naturally occurring microorganisms in clay rock and in the backfill material bentonite must be taken into account. Desulfosporosinus species play a crucial role in the community of sulfate-reducing bacteria present in clay rock and bentonite.[1,2] Desulfosporosinus hippei DSM 8344T is a close relative of the isolated species and was originally found in permafrost soils.[3] Desulfitobacterium sp. G1-2 has been isolated from bentonite samples and is an important representative of iron-reducing bacteria. As members of the microbial community from deep geological layers, these strains were selected to get a more profound knowledge about their interactions with U(VI). During time-dependent experiments in bicarbonate buffer (30 mM, 100 µM U(VI)), Desulfitobacterium sp. G1-2 showed a removal of up to 80% within 5 days. UV/Vis studies of the dissolved cell pellets verified the formation of U(IV) during the process. In contrast to these findings, Desulfosporosinus hippei DSM 8344T was not able to reduce U(VI) in the presence of bicarbonate. Therefore, experiments in artificial Opalinus Clay pore water [4] (100 µM U(VI), pH 5.5) were conducted. Determinations of the U concentrations showed a removal of up to 80% of the radionuclide from the supernatants within only 48 h. UV/Vis studies of the dissolved cell pellets provided clear proof of a partially reduction of U(VI) to U(IV), although bands of U(VI) were also still observable. These findings propose a combined association-reduction process as a possible interaction mechanism for this microorganism. TEM images combined with EDX analysis revealed the presence of two different U-containing aggregates in

The safe disposal of high-level radioactive waste in a deep geological repository is a huge social and scientific issue. So far, one of the less considered factors, especially in terms of a long-term risk assessment, is the impact of microorganisms occurring in the different host rocks. Even under the harsh conditions of salt formations different bacterial and archaeal species were found, e. g. Halobacterium sp. GP5 1-1, which has been isolated from a German rock salt sample. The interactions of this archaeon with uranium(VI), one of the major radionuclides of concern for the long-term storage of high-level radioactive waste, were investigated. Different spectroscopic techniques, as well as microscopy, were used to examine the occurring mechanisms on a molecular level leading to a more profound process understanding. Batch experiments with different uranium(VI) concentrations showed that the interaction is not only a simple, but a more complex combination of different processes. With the help of in situ attenuated total reflection Fourier-transform infrared spectroscopic investigations the association of uranium(VI) onto carboxylate groups was verified. In addition, time-resolved laser-induced luminescence spectroscopic investigations revealed the formation of a phosphate and carboxylate species within the cell pellets in dependence on the uranium(VI) concentration and the incubation time. Furthermore, the association behavior differs from another very closely related halophilic archaeon, especially with regard to uranium(VI) concentrations. This clearly demonstrates the importance of studying the interactions of different, at first sight very similar, microorganisms with uranium(VI). Overall, the findings presented in this work provide new insights into the microbe-uranium(VI) interactions at highly saline conditions relevant to the long-term storage of radioactive waste in rock salt.

The stored data sets represent both the raw data and the evaluated data that were used for the publication about uranium(VI) reduction by a sulfate-reducing bacterium.