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[en] Neptunium is found predominantly as Np(IV) in reducing environments, but as Np(V) in aerobic environments. Currently, it is not known how the interplay between biotic and abiotic processes affects Np redox speciation in the environment. To evaluate the effect of anaerobic microbial activity on the fate of Np in natural systems, Np(V) was added to a microcosm inoculated with anaerobic sediments from a metal-contaminated freshwater lake. The consortium included metal-reducing, sulfate-reducing, and methanogenic microorganisms, and acetate was supplied as the only exogenous substrate. Addition of more than 10-5 M Np did not inhibit methane production. Total Np solubility in the active microcosm, as well as in sterilized control samples, decreased by nearly two orders of magnitude. A combination of analytical techniques, including VIS-NIR absorption spectroscopy and XANES, identified Np(IV) as the oxidation state associated with the sediments. The similar results from the active microcosm and the abiotic controls suggest that microbially produced Mn(II/III) and Fe(II) may serve as electron donors for Np reduction
[en] Cement and concrete are the most important engineered barrier materials in a repository for low- and intermediate-level waste and thus represent the most significant component of the total disposal inventory. Based on the chemical composition of the concrete used in the repository and the groundwater fluxes in the modelled host rock, it is to be expected that the pH in the near vicinity of the repository could exceed a value of 10.5 for more than a million years. The groundwater in the repository environment also has a limited carbon concentration. Since microorganisms will be present in a repository and can even find suitable living conditions within the waste itself, investigations were carried out in order to establish the extent to which microbial activity is possible under the extreme conditions of the repository near-field. For the investigations, alkalophilic cultures were enriched from samples from alkaline habitats and from Valanginian Marl. Anaerobic bacteria with fermentative, sulfate-reducing and methanogenic metabolism were selected. The growth and activity of the mixed cultures were studied under alkaline conditions and the dependence on pH and carbon concentration determined. All the mixed cultures investigated are alkalophilic. The optimum growth range for the cultures is between pH 9.0 and pH 10.0. The activity limit for the fermentative mixed culture is at pH 12, for the sulfate-reducers at pH 11 and for the methanogens at pH 10.5. Given the limited supply of carbon, the mixed cultures can only grow under slightly alkaline conditions. Only the fermentative cultures are capable of surviving with limited carbon supply at pH 13. (author) 24 figs., 18 tabs., 101 refs
[en] Although the viscosity behavior of bacteria and extracellular polymeric substances (EPS) in flocculent activated sludge (FAS) and aerobic granular sludge (AGS) has been investigated, no studies have explored the role of viscosity in microbial attachment in pure culture. This study investigated the viscosity behavior of bacteria and EPS. The results showed that bacteria and their EPS exhibited non-Newtonian fluid and shear-thinning behavior. The viscosity of bacteria and EPS was 1.55–3.80 cP and 1.10–2.40 cP, respectively, while the attachment of bacteria (optical density at 600 nm) was 0.1426–3.1015. Bacteria with high attachment secreted EPS with a higher viscosity (2.40 cP), whereas those with weak attachment expressed EPS with a lower viscosity (1.10 cP). Viscosity and microbial attachment or extracellular polysaccharide (PS) content were significantly positively correlated. PS content was the source of bacterial viscosity, and β-polysaccharide played a more important role in viscosity and microbial attachment than α-polysaccharide. Thus, viscosity plays a critical role in microbial attachment, and high viscosity and PS content result in high microbial attachment, which is beneficial to the granulation process of AGS.
[en] A highly-efficient bioconjugation protocol of bimetallic rod-nanotags interacted with bacterial anti-S. aureus-IgG has been firstly demonstrated. Controllable fabrication of multilayer plasmonic nanorod-array (MPNRA) can be successfully obtained by facet functionalization of nanorods stacked on an activated Si/SiO2 chip. Vancomycin coating of MPNRA is favorable to immobilize S. aureus bacteria via multiple hydrogen bonding interactions, i.e., peptidoglycan of the bacterial cell and carbonyl/amine groups of the vancomycin. Moreover, the bimetallic rod-nanotags can be assembled around MPNRA via a bacterial biointerface. Ultrasensitive SERS detection of S. aureus bacteria with limit-of-detection (LOD) can be achieved up to 17.8 cfu/mL via combination of rod-nanotag and multilayer plasmonic nanorod-array perpendicular a chip (MPNRA-perpendicular substrate), which could be ascribed to dual plasmonic enhancement from bioconjugated rod-nanotags aggregates and large-scaled plasmonic nanorod-array.
[en] Although the ability of certain bacteria to generate electrical current was first described more than 100 years ago (Potter, 1911), it was not until the beginning of the present century that this phenomenon started to draw real interest from scientists and engineers. But don’t worry! you don’t have to wait 100 more years. Everything you always wanted to know and never asked about BES is here. But first of all, let’s examine what a BES is.
[en] The Prototype repository is an international project to build and study a full-scale model of the planned Swedish final repository for spent nuclear fuel. The Prototype consists of two sections with four and two full-scale copper canisters, respectively. In 2011, the outer section with two canisters (nos. 5 and 6) was excavated. Groundwater surrounding the Prototype has been demonstrated to include microorganisms such as iron-reducing bacteria (IRB) and sulphate-reducing bacteria (SRB) with the ability to affect the repository through reduction of structural Fe(III) in the buffer or by the production of sulphide, respectively. During excavation, samples were taken for microbiological and molecular biological analysis from backfill, buffer, and canister surfaces and analysed with an emphasis on microbial presence and number. The underground environment is anaerobic, but the construction of a repository will raise the oxygen levels. Oxygen is not favourable for the longevity of the copper canister, but oxygen levels will decrease over time, partly due to microbial activity that consumes oxygen. Therefore, evaluating the presence and numbers of the heterotrophic aerobic bacteria that consume oxygen as well as monitoring the oxygen levels are important. The oxygen content of the bentonite itself is also a primary concern, and a method for measuring how the oxygen diffuses through the clay has long been needed. In the work reported here, we performed two pilot studies to address this need. One of these studies tested a method for differentiating between oxygen saturation in aerobic versus anaerobic bentonite; this method has potential for further development. The tunnel above the Prototype canisters was backfilled with a mixture of bentonite and crushed rock. Sixty-three randomly chosen samples from a cross-section through the backfill were analysed for culturable heterotrophic aerobic bacteria. All but one exhibited growth, with four samples exhibiting numbers over 106 colony-forming units per gram wet weight (CFU gww-1). These four samples were all taken near the tunnel ceiling, supporting the possibility of an influx of nutrients from surrounding groundwater. This milieu seems to favour SRB over IRB, according to the most probable number (MPN) results for these samples. Microbial numbers in buffer and on canister surfaces seem to be low judging from the present results. However, from samples from buffer areas with high water saturation and low density, i.e. three samples from buffer ring 5 in deposition hole 6, we were able to grow up to 1.3 X 104 cells gww-1 in IRB medium. DNA from these samples was extracted and then sequenced to obtain information about the species cultivated. Alignment indicated that species of anaerobic thermophilic bacteria, such as Thermacetogenium phaeum, and other aerobic bacteria with the potential to form spores, such as Thermaerobacter subterraneus, could be found in the buffer. These bacteria must have been dormant since the formation of the bentonite blocks, but are obviously still viable when given appropriate growing conditions. Molecular biology methods were also able to find traces of SRB on canister surfaces, though these bacteria were not viable and could not be cultivated
[en] Fluoroquinolones like difloxacin (DIF) and sarafloxacin (SARA) are adsorbed in soil and enter the aquatic environment wherein they are subjected to photolytic degradation. To evaluate the fate of DIF and SARA, their photolysis was performed in water under stimulated natural sunlight conditions. DIF primarily degrades to SARA. On prolonged photodegradation, seven photoproducts were elucidated by HR-LC-MS/MS, three of which were entirely novel. The residual anti-bacterial activities of DIF, SARA and their photoproducts were studied against a group of pathogenic strains. DIF and SARA revealed potency against both Gram-positive and -negative bacteria. The photoproducts also exhibited varying degrees of efficacies against the tested bacteria. Even without isolating the individual photoproducts, their impact on the aquatic environment could be assessed. Therefore, the present results call for prudence in estimating the fate of these compounds in water and in avoiding emergence of resistance in bacteria caused by the photoproducts of DIF and SARA. - Assessment of the residual anti-bacterial efficacies of difloxacin, sarafloxacin and their photoproducts in water, and estimating their impact on the aquatic environment in inducing resistance to microorganisms.
[en] Cupriavidus SRS is a metal resistant, rod shaped, gram negative bacteria that was isolated from a location with heavy metal contamination at the Department of Energy’s Savannah River Site in Aiken, South Carolina. This isolate has also been able to demonstrate antibiotic resistance and predatory behavior to other microorganisms, giving it a competitive advantage. The effect of bioaugmentation with Cupriavidus SRS and copper (Cu) uptake is not well understood, although multiple studies have analyzed this effect with other metal resistant bacteria. In this study, sediment from the AL1 outfall area will be inoculated with Cupriavidus SRS to analyze the effectiveness of the degradation of Cu.
[en] The aim of this work was to perform a critical evaluation of this mechanism of metal accumulation in selected strains of bacteria. A ''Citrobacter freundii'' and some other strains of bacteria isolated from soil polluted by heavy metals were used. All these strains exhibited an enhanced activity of an acid-type phosphatase with a pH optimum at pH 5 typical of microorganisms. Time course of accumulation of uranium (in the form of 0.1 mM uranyl nitrate) by these bacteria was followed in a substrate-less system and at increasing concentrations (from 1 to 16 mM) of glycerol-2-phosphate as a substrate for the phosphatase. It was found that at low glycerol-2-phosphate concentrations (1.0 mM) the bacteria accumulated about 30% uranium more than in a substrate-less system. At higher glycerol-2-phosphate concentrations less metal was accumulated. Electron microscopic observation of ultra thin sections of cells revealed that metal was located mainly at the surface as a dense precipitate. It was presumed that an observed inhibition of uranium accumulation could be connected with a formation of soluble uranyl compounds with glycerol-2-phosphate within a pH of 5 to 6. Such a presumption was confirmed by revealing a 60 to 80% uranium recovery from the loaded cells in 10 mM glycerol-2-phosphate solution. (author). 13 refs, 10 figs, 1 tab