Dirk Merten

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.

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.

Growth of streptomycetes in soil and their impact on bioremediation.

The impact of the extremely heavy metal resistant actinomycete Streptomyces mirabilis P16B-1 on heavy metal mobilization/stabilization, phytoremediation and stress level of plants was analyzed in the presence and absence of Sorghum bicolor in sterile microcosms containing highly metal contaminated or control soil. For control, a metal sensitive S. lividans TK24 was used. The metal contents with respect to the mobile and specifically adsorbed fractions of the contaminated soil were considerably decreased by addition of both, living and dead biomass of the strains, with the heavy metal resistant S. mirabilis P16B-1 showing considerably higher impact. Both strains could grow in control soil, while only S. mirabilis P16B-1 formed new tip growth in the metal contaminated soil. A plant growth promoting effect was visible for S. mirabilis P16B-1 in contaminated soil enhancing the dry weight of inoculated Sorghum plants. Thus, metal resistant strains like S. mirabilis P16B-1 are able to enhance phytoremediation of heavy metal contaminated soils.

Rare Earth Elements in Acidic Systems – Biotic and Abiotic Impacts

Rare earth elements (REE) are heavy metals with increasing technical application and importance in science. They are found in minerals like monazite and bastnaesite, which contain especially La and Ce. In waters, REE abundance strongly depends on pH, with acid mine drainage influence resulting in higher REE concentrations. The range of REE in solids as well as in precipitation, river water, seawater, and groundwater without AMD influence, and in acidic waters is reviewed. When plotting REE abundances against the atomic numbers, the natural REE abundance shows a characteristic zig-zag pattern due to the higher stability of even masses. To recognize slight variations in the behavior of REE in different samples, concentrations are normalized to a reference standard resulting in a characteristic graph called REE pattern. These patterns can be used to identify processes leading to different distributions, e.g., related to the influence of microorganisms. In AMD-influenced areas, consortia of microorganisms adapted to these conditions colonize the soils. These organisms can tolerate high metal concentrations, low pH conditions, and low nutrient supply. In bioremediation, such microorganisms are applied to improve the metal uptake from soil into plants since they support the element solubilization and transfer. However, bacteria and fungi are also able to stabilize metals in the soil by intracellular or extracellular complexation, thus minimizing the translocation to plants, depending on species and environmental conditions. To differentiate processes, REE may be applied which is discussed in this chapter.

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.

Phytoextraction of Heavy Metals by Dominating Perennial Herbs

The cosmopolitan perennials, giant goldenrod and stinging nettle reach with 6.2–11.3 t ha–1 (DW) the biomass production of those annual crops which are recommended for heavy metal extractions from soils but share with those the intolerable cleanup times. Due to their economic and environmental advantages, cropping rod and nettle, e.g., as renewable energy sources, is an interesting variant in the (remediative) use of heavy-metal contaminated soils.

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.

Microbial communities in carbonate rocks—from soil via groundwater to rocks

Microbial communities in soil, groundwater, and rock of two sites in limestone were investigated to determine community parameters differentiating habitats in two lithostratigraphic untis. Lower Muschelkalk and Middle Muschelkalk associated soils, groundwater, and rock samples showed different, but overlapping microbial communities linked to carbon fluxes. The microbial diversities in soil were highest, groundwater revealed overlapping taxa but lower diversity, and rock samples were predominantly characterized by endospore forming bacteria and few archaea. Physiological profiles could establish a differentiation between habitats (soil, groundwater, rock). From community analyses and physiological profiles, different element cycles in limestone could be identified for the three habitats. While in soil, nitrogen cycling was identified as specific determinant, in rock methanogenesis linked carbonate rock to atmospheric methane cycles. These patterns specifically allowed for delineation of lithostratigraphic connections to physiological parameters.

Geomicrobial Manganese Redox Reactions in Metal-Contaminated Soil Substrates

Geomicrobial cycles influence metal mobilities in soil. The formation of Fe and Mn(hydr)oxides in biogeochemical horizons and the subsequent mobilization of Mn from the substrate can lead to high mobility of Mn. This process of Mn mobilization was studied in substrates derived from a former uranium mining area in column experiments. Microbially influenced manganese release was investigated in columns with an autochthonous microbial community and columns additionally inoculated with Streptomyces. Additionally, azide-poisoned columns were analyzed. Levels of 1,060 μg l−1 Mn(II) were released from inoculated columns while batch experiments led to elution of up to 28 μg l−1 Mn(II). The microbial influence on element cycling correlated with decreasing redox potentials. To study the potential of microbial reduction processes, strains isolated from these columns were investigated. One prominent bacterium, identified as Cupriavidus metallidurans, tolerated up to 30 mM Mn(II). However, no aerobic microbial Mn reduction was found indicating that Mn release was either dependent on anaerobic conditions, or microbial respiration initiated abiotic Mn reduction by decreasing the redox potential necessary for these processes.