Georg Büchel

Siderophores mediate reduced and increased uptake of cadmium by Streptomyces tendae F4 and sunflower (Helianthus annuus), respectively

Aims:  As a toxic metal, cadmium (Cd) affects microbial and plant metabolic processes, thereby potentially reducing the efficiency of microbe or plant‐mediated remediation of Cd‐polluted soil. The role of siderophores produced by Streptomyces tendae F4 in the uptake of Cd by bacteria and plant was investigated to gain insight into the influence of siderophores on Cd availability to micro‐organisms and plants.

Microbial links between sulfate reduction and metal retention in uranium- and heavy metal-contaminated soil.

ABSTRACT Sulfate-reducing bacteria (SRB) can affect metal mobility either directly by reductive transformation of metal ions, e.g., uranium, into their insoluble forms or indirectly by formation of metal sulfides. This study evaluated in situ and biostimulated activity of SRB in groundwater-influenced soils from a creek bank contaminated with heavy metals and radionuclides within the former uranium mining district of Ronneburg, Germany. In situ activity of SRB, measured by the 35SO42− radiotracer method, was restricted to reduced soil horizons with rates of ≤142 ± 20 nmol cm−3 day−1. Concentrations of heavy metals were enriched in the solid phase of the reduced horizons, whereas pore water concentrations were low. X-ray absorption near-edge structure (XANES) measurements demonstrated that ∼80% of uranium was present as reduced uranium but appeared to occur as a sorbed complex. Soil-based dsrAB clone libraries were dominated by sequences affiliated with members of the Desulfobacterales but also the Desulfovibrionales, Syntrophobacteraceae, and Clostridiales. [13C]acetate- and [13C]lactate-biostimulated soil microcosms were dominated by sulfate and Fe(III) reduction. These processes were associated with enrichment of SRB and Geobacteraceae; enriched SRB were closely related to organisms detected in soils by using the dsrAB marker. Concentrations of soluble nickel, cobalt, and occasionally zinc declined ≤100% during anoxic soil incubations. In contrast to results in other studies, soluble uranium increased in carbon-amended treatments, reaching ≤1,407 nM in solution. Our results suggest that (i) ongoing sulfate reduction in contaminated soil resulted in in situ metal attenuation and (ii) the fate of uranium mobility is not predictable and may lead to downstream contamination of adjacent ecosystems.

Heavy Metal Tolerance of Fe(III)-Reducing Microbial Communities in Contaminated Creek Bank Soils

ABSTRACT Fe(III)-reducing soil enrichment cultures can tolerate 100 μM Cu and Cd, 150 μM Co, 600 μM Ni, and 2,500 μM Zn. Metal-tolerant cultures were dominated by Geobacter-related Deltaproteobacteria and Gram-positive Firmicutes spp. (Clostridia and Sedimentibacter). A Cd- and Cu-tolerant Fe(III)-reducing coculture of Desulfosporosinus and Desulfitobacterium indicated the importance of the Firmicutes for Fe(III) reduction in the presence of metals.

Identification of Mn(II)-Oxidizing Bacteria from a Low-pH Contaminated Former Uranium Mine

ABSTRACT 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.

Phytoremediation using microbially mediated metal accumulation in Sorghum bicolor

Reclaiming land that has been anthropogenically contaminated with multiple heavy metal elements, e.g., during mining operations, is a growing challenge worldwide. The use of phytoremediation has been discussed with varying success. Here, we show that a careful examination of options of microbial determination of plant performance is a key element in providing a multielement remediation option for such landscapes. We used both (a) mycorrhiza with Rhizophagus irregularis and (b) bacterial amendments with Streptomyces acidiscabies E13 and Streptomyces tendae F4 to mediate plant-promoting and metal-accumulating properties to Sorghum bicolor. In pot experiments, the effects on plant growth and metal uptake were scored, and in a field trial at a former uranium leaching heap site near Ronneburg, Germany, we could show the efficacy under field conditions. Different metals could be extracted at the same time, with varying microbial inoculation and soil amendment scenarios possible when a certain metal is the focus of interest. Especially, manganese was extracted at very high levels which might be useful even for phytomining approaches.

Evaluation of groundwater dynamics and quality in the Najd aquifers located in the Sultanate of Oman

The Najd, Oman, is located in one of the most arid environments in the world. The groundwater in this region is occurring in four different aquifers A to D of the Hadhramaut Group consisting mainly of different types of limestone and dolomite. The quality of the groundwater is dominated by the major ions sodium, calcium, magnesium, sulphate, and chloride, but the hydrochemical character is varying among the four aquifers. Mineralization within the separate aquifers increases along the groundwater flow direction from south to north-northeast up to high saline sodium-chloride water in aquifer D in the northeast area of the Najd. Environmental isotope analyses of hydrogen and oxygen were conducted to monitor the groundwater dynamics and to evaluate the recharge conditions of groundwater into the Najd aquifers. Results suggest an earlier recharge into these aquifers as well as ongoing recharge takes place in the region down to present day. Mixing of modern and submodern waters was detected by water isotopes in aquifer D in the mountain chain (Jabal) area and along the northern side of the mountain range. In addition, δ2H and δ18O variations suggest that aquifers A, B, and C are assumed to be connected by faults and fractures, and interaction between the aquifers may occur. Low tritium concentrations support the mixing assumption in the recharge area. The knowledge about the groundwater development is an important factor for the sustainable use of water resources in the Dhofar region.

UMBRELLA: Using MicroBes for the REgulation of heavy metaL mobiLity at ecosystem and landscape scAle

This special issue focuses on metal-contaminated areas resulting from mining activities. These sites are characterized by low nutrient availability, poor soil quality, and low pH, in addition to high metal loads. The contamination at former mining sites most often is associated with acid mine drainage leading to the dispersal of metals. The resulting areas are compromised with respect to both use of land for, e.g., agronomy and forestry, and groundwater, the main source of drinking water, restricting future use. In addition, the contamination can spread, if not attended to, contaminating additional, previously non-contaminated ecosystems. Government regulations for effective management of contaminated sites exist worldover, and reclamation of acid mine drainage-influenced areas attracts growing interest. Remediation actions are necessary, which, in addition to geo-engineering strategies, increasingly include monitored natural attenuation and bioremediation. This needs to be based on a detailed understanding of processes in bio-geo interactions at metal-contaminated sites, which is addressed here to provide an integrated approach summarized in a scheme for useful application of each of these remediation actions shown in this special issue at a generalized former mining site. The proposed applications help to minimize the risk to human health and environmental impact and are cost-efficient. Soil is the basis of terrestrial life and has a major impact on human life through its use for agriculture, forestry, or general land use. In addition, it remains the largest terrestrial ecosystem that is shaped by high numbers of microorganisms and plant roots. The metabolic activities of both microorganisms and plants sustain pedogenesis which, however, differs with respect not only to base rock material and climatic conditions, but also to, e.g., pollution. Root exudates as well as microbiological acidification and release of chelating agents take part in heavy metal mobilization and immobilization processes, which are of high impact at metal-rich sites. The ecotoxicologically relevant heavy metal concentrations are dependent on interaction with soil particles and microbial surfaces; hence, inoculation strategies may improve future land use. Mobilization and distribution pathways for metals from source, where geo-engineering techniques may be deployed, to sink need to be re-evaluated. Nature has evolved ecosystems able to cope with high metal loads, and by learning from the evolutionary and biological processes, it may be feasible to adopt additional strategies for bioremediation. During natural attenuation, new minerals can be formed. This might lead to supergenic ore formation and hence provides means to even use these metals without disturbing new, natural sites. In this special issue, we will discuss all mentioned mobilization and immobilization mechanisms to contribute to a general understanding of bioremediation potentials. Thus, we may draw on the potential of natural attenuation instead of premature application of high-cost geo-engineering, depending on sitespecific parameters. This concept will allow for the reduction of the costs of an estimated 38 billion Euro per year incurred by society at large for soil destruction and environmental degradation. The formation of acid mine drainage (AMD) or also of acid rock drainage (ARD) is a process related to unearthing metal ores, many of which are sulfidic ores. Similar processes leading to AMD apply to coal mining, since coal also contains sulfur in pyrite and marcasite as well as organically bound sulfur. The anoxic environment in the mine does provide Responsible editor: Philippe Garrigues

Phytoremediation as an Alternative Way for the Treatment of Large, Low Heavy Metal Contaminated Sites: Application at a Former Uranium Mining Area

Large sites with a low contamination of metall(oid)s were in the past a problem for remediation measures – the “traditional” processes were too expensive for an application on such expanded areas. Phytoremediation can be an alternative for such low contamination problems. In Germany, a research project is performed on this subject, in cooperation of the University of Jena and the TU Dresden. The field site is a former U mining area. Until 1991, a low grade U ore dump for sulfuric acid leaching was located on this site. After the close-down of the U mining in East Germany in 1991, the dump material was removed. Now, a phytoremediation test field is constructed on top of this site for the capture of the remained contaminants coming up by capillary forces. The paper pictures the phytoremediation in general, the research project and gives some first preliminary results.

Soil treatment with nitrogen facilitates continuous phytoextraction of heavy metals

NH4Cl was the optimum N compound to make soil heavy metals more plant-available but less leachable, and to increase biomass production, root uptake, and translocation to the shoot of Cd, Co, Cu, Mn, Ni, and Zn in Chinese cabbage. Their total weight in the shoots of higher biomass increased to 765 %.

Aquifer community structure in dependence of lithostratigraphy in groundwater reservoirs

Groundwater microbiology with respect to different host rocks offers new possibilities to describe and map the habitat harboring approximately half of Earths’ biomass. The Thuringian Basin (Germany) contains formations of the Permian (Zechstein) and Triassic (Muschelkalk and Buntsandstein) with outcrops and deeper regions at the border and central part. Hydro(geo)chemistry and bacterial community structure of 11 natural springs and 20 groundwater wells were analyzed to define typical patterns for each formation. Widespread were Gammaproteobacteria, while Bacilli were present in all wells. Halotolerant and halophilic taxa were present in Zechstein. The occurrence of specific taxa allowed a clear separation of communities from all three lithostratigraphic groups. These specific taxa could be used to follow fluid movement, e.g., from the underlying Zechstein or from nearby saline reservoirs into Buntsandstein aquifers. Thus, we developed a new tool to identify the lithostratigraphic origin of sources in mixed waters. This was verified with entry of surface water, as species not present in the underground Zechstein environments were isolated from the water samples. Thus, our tool shows a higher resolution as compared to hydrochemistry, which is prone to undergo fast dilution if water mixes with other aquifers. Furthermore, the bacteria well adapted to their respective environment showed geographic clustering allowing to differentiate regional aquifers.