The commonly observed enrichment of middle rare earth elements (MREE) in water sampled in acid mine drainage (AMD)-impacted areas was found to be the result of preferential release from the ...widespread mineral pyrite (FeS₂). Three different mining-impacted sites in Europe were sampled for water, and various pyrite samples were used in batch experiments with diluted sulphuric acid simulating AMD-impacted water with high sulphate concentration and high acidity. All water samples independent on their origin from groundwater, creek water or lake water as well as on the surrounding rock types showed MREE enrichment. Also the pyrite samples showed MREE enrichment in the respective acidic leachate but not always in their total contents indicating a process-controlled release. It is discussed that most probably complexation to sulphite (SO₃ ²⁻) or another intermediate S-species during pyrite oxidation is the reason for the MREE enrichment in the normalized REE patterns.
Natural Mn oxides are largely biogenic in origin, formed via the microbial oxidation of Mn(II). These minerals are extremely efficient scavengers of heavy metals, yet to date microbial Mn oxide ...precipitation and subsequent heavy metal sorption have received little attention in mining-impacted environments, where heavy metal concentrations are elevated but (bio)geochemical conditions are typically unfavourable for both abiotic and biogenic Mn oxide precipitation, featuring acidic pH and low organic carbon contents. Here we investigate the formation of Mn oxide (bio)geochemical barrier layers, and the immobilisation of heavy metals in these layers, in soil profiles from a former uranium mining site in Ronneburg, Germany. Detailed soil profiling shows the site has an acidic soil pH that varies from 4.7 to 5.1 and Eh values from 640 to 660mV. Using synchrotron X-ray diffraction and X-ray absorption spectroscopy, together with scanning electron microscopy and electron microprobe analysis, we find that the dominant Mn oxide present in the Mn oxide layers is a poorly crystalline hexagonal birnessite, akin to synthetic δ-MnO2, covering and cementing quartz grains. Using phylogenetic analysis based on 16S rDNA, we identify and characterise six strains of manganese oxidising bacteria (MOB) from the acidic Mn oxide layers which we subsequently culture to produce poorly crystalline hexagonal birnessite akin to that found at the study site. Specifically, we identify three Gram-positive spore-forming firmicutes affiliated to Bacillus safensis, Bacillus altitudinis and Brevibacillus reuszeri, which are able to oxidise Mn after initiating spore formation, two Gram-positive actinobacteria belonging to the genera Arthrobacter and Frondihabitans, and one Gram-negative proteobacteria belonging to the genus Sphingomonas. Geochemical thermodynamic speciation modelling indicates that the abiotic precipitation of Mn oxides in the Mn oxide layers is unfavourable and we suggest that the Mn oxides in the (bio)geochemical barriers at our study site are biogenically precipitated in an acidic soil environment. To our knowledge, this is the first report to identify the above six bacterial strains, and specifically identify spore-forming bacteria, as MOB in an acidic soil environment. We find that the poorly crystalline hexagonal birnessite precipitated in the Mn oxide layers efficiently immobilises Ba, Ni, Co, Cd, Zn and Ce, and as such we find that MOB and biogenically precipitated Mn oxides can exert a strong control on the fate and mobility of metals in mining-impacted environments.
•We investigate the origin of and metal retention on Mn oxides in Mn oxide layers at a mining-impacted site with acidic pH.•We identify Mn oxidising bacteria and precipitation of biogenic Mn oxides in the Mn oxide layers at acidic soil pH.•This is the first report to identify spore-forming bacteria as Mn oxidisers in an acidic environment.•The biogenic Mn oxide is poorly crystalline hexagonal birnessite.•The biogenic Mn oxide efficiently immobilises Ba, Ni, Co, Cd, Zn and Ce at acidic soil pH.
Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation ...in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 (Duganella isolate AB_14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments.
High levels of metals impede plant growth by affecting physiological processes. Siderophores are microbial Fe-chelators that, however, bind other metals. This study evaluated plant growth in a soil ...containing elevated levels of metals, including Al, Cu, Fe, Mn, Ni, and U, using
Streptomyces-derived cell-free supernatant containing siderophores and auxins. Cowpea plants in the soil were treated with the culture filtrate. Growth was measured and biochemical analyses such as chlorophyll contents, RNA and protein quantification, lipid membrane peroxidation, and anti-oxidative responses were conducted to evaluate oxidative stress in the plants. Liquid chromatography–mass spectrometry was used to simulate competition for siderophore binding, and metal content of plants was determined spectroscopically. Whereas the metals inhibited plant growth, addition of siderophores improved growth. There was evidence of lipid peroxidation, an enhanced superoxide dismutase activity, and lowered chlorophyll, RNA, protein, carotenoid and residual indole acetic acid contents, especially in control plants. Siderophore competition assays between Al and Fe, and Fe and Cu suggested that trivalent metals are more competitive for siderophore binding than divalent ones. Compared to control plants, higher amounts of metals were obtained in siderophore-treated plants. Siderophores were able to supply plants with Fe in the presence of levels of metals, mainly Al, Cu, Mn, Ni and U that otherwise inhibit Fe acquisition. This led to enhanced chlorophyll content, circumventing lipid peroxidation effects on leaves. Siderophores lowered the formation of free radicals, thereby protecting microbial auxins from degradation and enabling them to enhance plant growth which in turn resulted in augmented metal uptake.
The siderophore-producing ability of nickel-resistant
Streptomyces acidiscabies
E13 and the role of the elicited siderophores in promoting plant growth under iron and nickel stress are described. ...Siderophore assays indicated that S. acidiscabies E13 can produce siderophores. Electrospray ionization mass spectrometry (ESI-MS) revealed that the bacterium simultaneously produces 3 different hydroxamate siderophores. ESI-MS showed that in addition to iron, all 3 siderophores can bind nickel. In vitro plant growth tests were conducted with cowpea (
Vigna unguiculata
) in the presence and absence of the elicited siderophores. Culture filtrates containing hydroxamate siderophores significantly increased cowpea height and biomass, irrespective of the iron status of the plants, under nickel stress. The presence of reduced iron was found to be high in siderophore-containing treatments in the presence of nickel. Measurements of iron and nickel contents of cowpea roots and shoots indicated that the siderophore-mediated plant growth promotion reported here involves the simultaneous inhibition of nickel uptake and solubilization and supply of iron to plants. We conclude that hydroxamate siderophores contained in culture filtrates of S. acidiscabies E13 promoted cowpea growth under nickel contamination by binding iron and nickel, thus playing a dual role of sourcing iron for plant use and protecting against nickel toxicity.
Single particle inductively coupled plasma mass spectrometry (spICP-MS) is a well-established technique to characterize the size, particle number concentration (PNC), and elemental composition of ...engineered nanoparticles (NPs) and colloids in aqueous suspensions. However, a method capable of directly analyzing water-sensitive or highly reactive NPs in alcoholic suspension has not been reported yet. Here, we present a novel spICP-MS method for characterizing the main cement hydration product, i.e., calcium-silicate-hydrate (C-S-H) NPs, in ethanolic suspensions, responsible for cement strength. The method viability was tested on a wide range of NP compositions and sizes (i.e., from Au, SiO2, and Fe3O4 NP certified reference materials (CRMs) to synthetic C-S-H phases with known Ca/Si ratios and industrial cement hardening accelerators, X-Seed 100/500). Method validation includes comparisons to nanoparticle tracking analysis (NTA) and transmission/scanning electron microscopy (TEM/SEM). Results show that size distributions from spICP-MS were in good agreement with TEM and NTA for CRMs ≥ 51 nm and the synthetic C-S-H phases. The X-Seed samples showed significant differences in NP sizes depending on the elemental composition, i.e. CaO and SiO2 NPs were bigger than Al2O3 NPs. PNC via spICP-MS was successfully validated with an accuracy of 1 order of magnitude for CRMs and C-S-H phases. The spICP-MS Ca/Si ratios matched known ratios from synthetic C-S-H phases (0.6, 0.8, and 1.0). Overall, our method is applicable for the direct and element-specific quantification of fast nucleation and/or mineral formation processes characterizing NPs (ca. 50–1000 nm) in alcoholic suspensions.
Heavy metal-contaminated soil derived from a former uranium mining site in Ronneburg, Germany, was used for sterile mesocosms inoculated with the extremely metal-resistant Streptomyces mirabilis ...P16B-1 or the sensitive control strain Streptomyces lividans TK24. The production and fate of bacterial hydroxamate siderophores in soil was analyzed, and the presence of ferrioxamines E, B, D, and G was shown. While total ferrioxamine concentrations decreased in water-treated controls after 30 days of incubation, the sustained production by the bacteria was seen. For the individual molecules, alteration between neutral and cationic forms and linearization of hydroxamates was observed for the first time. Mesocosms inoculated with biomass of either strain showed changes of siderophore contents compared with the non-treated control indicating for auto-alteration and consumption, respectively, depending on the vital bacteria present. Heat stability and structural consistency of siderophores obtained from sterile culture filtrate were shown. In addition, low recovery (32 %) from soil was shown, indicating adsorption to soil particles or soil organic matter. Fate and behavior of hydroxamate siderophores in metal-contaminated soils may affect soil properties as well as conditions for its inhabiting (micro)organisms.
Action by the para: Evaluation of the nitro‐group‐forming N‐oxygenase AurF in vivo, in vitro, and immobilized as a fusion protein with simply H2O2 as oxidant (peroxide shunt) reveals ...para‐regioselective oxygenation of aromatic amines (see scheme). This effect includes the selective oxygenation of diamino compounds.
A site in the former uranium mining area of Eastern Thuringia near Ronneburg was investigated with regard to effects of acid mine drainage (AMD) on reactive transport and bioattenuation. Processes ...involved in this attenuation might include physico-chemical reactions in reactive transport as well as activities of microorganisms for bioattenuation. In order to test the influence of the soil microbes, a mapping was carried out including both hydrogeochemical and microbiological parameters.
Mapping of contamination was performed along the banks of a creek in a 900
m stretch in 50
m steps by hydrogeochemical analysis of water extracts of soil samples, while general microbial activity was scored by examining soil respiration. The soil samples with high heavy metal load did show low soil respiration as a parameter for microbial activity and plating revealed minimal counts for spore producing bacteria at these contaminated locations. Actinobacteria strains isolated from adjacent locations revealed high levels of resistance as well as high numbers of resistant strains. Specific responses in actinobacteria were investigated after isolation from each of the 18 measuring points along the creek. Specific adaptation strategies and high yields of (intra)cellular heavy metal retention could be seen. Several strategies for coping with the high heavy metal contents are further discussed and genes for proteins expressed specifically under high nickel concentration were identified by two-dimensional gel electrophoresis.
Streptomyces are important soil bacteria used for bioremediation of metal-contaminated soils, however, it is still unknown how metal-selective Streptomyces are and which mechanisms are involved ...during their capture. In this work, we exposed S. coelicolor spores to environmentally relevant concentrations (0.1, 1, 10, 100 μM) of Ce, U and Cd in solid medium for one week to investigate the uptake behaviour of hyphae in the newly formed spores. Additionally, metal adsorption onto the spores was explored by incubating inactive, ungerminated spores for one day in aqueous metal solution. The spore-washing treatment was key to distinguishing between strongly spore-associated (e.g. incorporation; Tris-EDTA buffer) and weakly spore-associated metals (Tris buffer alone minus Tris-EDTA). Single cell (sc) ICP-MS was used to quantify metal-associated content in individual spores. Our results revealed element-specific adsorption onto inactive spores showing that out of the total metal exposure, both strongly (Ce: 58%; U: 54%; Cd: 28%) and weakly (Ce: 12%; U: 1%; Cd: 18%) adsorbed metals occur. However, scICP-MS showed that from metal-amended solid medium, only Ce and U were strongly spore-associated (averages 0.040 and 0.062 fg spore−1 for 10 μM exposures, respectively) while Cd was below the limit of detection (< 0.006 fg spore−1). We propose that hyphae only metabolically interact with Ce in a controlled manner but uncontrolled with U, as 66–73% Ce and only 2–4% U were inherited from adsorbed content. We conclude that Streptomyces spore-metal interaction starts with a relevant adsorption step of Ce, U and Cd as presented for aqueous conditions. If spores start to germinate, hyphae are capable of effectively encapsulating Ce and U, but not Cd. This study brings light into the still unknown field of metal interactions with Streptomyces and applied understanding for more efficient and metal-specific use of Streptomyces in bioremediation of metal-polluted soils.
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•Single cell ICP-MS was used to quantify metal association with spores.•Distinction between weak adsorption and strong association (metal-spore).•Ce, U and Cd showed spore-adsorption in aqueous conditions.•Ce and U were strongly spore-associated after growing in metal-amended solid medium.•Spore association metabolically controlled for Ce and uncontrolled for U.
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