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| 3. |
- Duckworth, O W, et al.
(författare)
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Biogeochemistry of iron oxidation in a circumneutral freshwater habitat
- 2009
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 260:3-4, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- Iron(II) oxidation in natural waters at circumneutral pH, often regarded as an abiotic process, is frequently biologically mediated at iron-rich redox gradients. West Berry Creek, a small circumneutral tributary that flows through a mixed coniferous forest in Big Basin State Park, California, contains localized iron (hydr)oxide precipitates at points along its course where anoxic groundwater meets oxygenated creek water. These mixing zones establish redox gradients that may be exploited by microbes forming microbial mats that are intimately associated with iron (hydr)oxide precipitates. Water sampling revealed strong correlations between the concentrations of aqueous inorganic species, suggesting a rock-weathering source for most of these solutes. Liquid chromatography-electrospray ionization-mass spectrometry techniques detected significant concentrations of organic exudates, including low molecular mass organic acids and siderophores, indicating that active biogeochemical cycling of iron is occurring in the creek. X-ray diffraction and elemental analysis showed the precipitates to be amorphous, or possibly poorly crystalline, iron-rich minerals. Clone libraries developed from 16S rDNA sequences extracted from microbial mat communities associated with the precipitates revealed the presence of microorganisms related to the neutrophilic iron oxidizing bacteria Gallionella and Sideroxydans. Sequences from these libraries also indicated the presence of significant populations of organisms related to bacteria in the genera Aquaspirillum, Pseudomonas, Sphingomonas, and Nitrospira. These geosymbiotic systems appear to be significant not only for the biogeochemical cycling of iron in the creek, but also for the cycling of organic species, inorganic nutrients, and trace metals.
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| 4. |
- Edberg, Frida, 1966-
(författare)
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Bacteria and geochemistry in a former uranium open pit mine - mobilization of trace metals
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In mining areas around the world, chemical and biotic processes have lead to the release of toxic substances, e.g. metals. Microbial processes influence metal speciation, while the chemical environment shapes and controls microbial populations. This thesis has two parts and the papers cover various aspects of metal-to-microbe links in a former uranium mine at Ranstad, Sweden. The first part of the thesis examines bacteria-induced metal mobilization by the cultivation of Pseudomonas fluorescens with ore and minerals from the Ranstad mine. The presence of a mineral source stimulated bacterial growth. Pyoverdine-type siderophores typical for P. fluorescens were produced, but also other types of siderophores. The bacterial mobilization of metals is implied by the agreement in concentrations of Fe-pyoverdine complex and soluble Fe, and by the concentrations of Ni and Co in solution. U was mobilized from the ore as a result of bacterial growth raising pH. The second part of the thesis focus on the partitioning of metals and their links to the microbial communities in the water of the former open pit mine, Lake Tranebärssjön. The lake was pH-neutral to alkaline, highly stratified, and had an anoxic hypolimnion with high concentrations of metals and SO42-. Size fractionation showed the dissolved fraction dominating for most metals, while the particulate and colloidal fractions dominated for Fe. Chemical equilibrium models agreed reasonably well with these results. In the pyrosequencing study of the bacterial community, depth-related changes in water chemistry corresponded to a distinct shift in the microbial community, indicating a chemical control. The presence of metal- and SO42--reducing bacteria suggests a possible microbe – chemistry connection. The findings of this thesis could be used for the restoration and remediation of mining sites, and provides information on factors governing the establishment and control of bacterial populations in freshwaters.
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| 5. |
- Ahmed, Engy, et al.
(författare)
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Microbe-mineral interactions : The impact of surface attachment on mineral weathering and element selectivity by microorganisms
- 2015
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 403, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- One of the major gaps within the field of biogeochemistry is the lack of a detailed and deep understanding of the mechanismbehind the microbial inducement of mineral dissolution. The association of microorganisms with the mineral surfaces is an important issue for understanding processes like mineral weathering, biomineralization, bioremediation and biofouling. The present study aims to investigate the performance of attached and unattached soil fungal and bacterial species in biotite weathering and in the selectivity of elements from biotite. Sterilized microplate devices were filled with biotite (>2 mm) followed by an iron limited liquid growth medium and were inoculated separately with six different microbial species isolated from podzol soil: Erwinia amylovora, Pseudomonas stutzeri, Pseudomonas mendocina, Streptomyces pilosus, Neurospora crassa and Penicillium melinii. The experiment was designed in two set-ups: 1) attached form, in which the microorganisms were inoculated directly to the biotite surface, and 2) unattached form, in which 0.4 mu m PET track etched devices were used to separate the microbial cells from the biotite surface. Our findings indicate that the surface attached microorganisms led to a greater dissolution of elements from biotite than the unattached microorganisms that was evidenced by 1) higher dissolution of Fe, Al and Si, 2) greater decrease in pH of the liquid growth medium, and 3) relatively higher production of siderophores. Furthermore, there was no significant difference in the capability of element selectivity between the attached and unattached microbial forms. The biotite dissolution was promoted initially by complexation processes and later by acidification processes for most of the attached and unattached microorganisms. Thus, we conclude that despite the mineral dissolution induced by microbial attachment on the mineral surface, the element composition of the biotite and nutritional need of the microorganisms were the main factors affecting the element selectivity.
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| 6. |
- Ahmed, Engy, et al.
(författare)
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Mineral Type Structures Soil Microbial Communities
- 2017
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Ingår i: Geomicrobiology Journal. - : Taylor & Francis. - 0149-0451 .- 1521-0529. ; 34:6, s. 538-545
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Tidskriftsartikel (refereegranskat)abstract
- Soil microorganisms living in close contact with minerals play key roles in the biogeochemical cycling of elements, soil formation, and plant nutrition. Yet, the composition of microbial communities inhabiting the mineralosphere (i.e., the soil surrounding minerals) is poorly understood. Here, we explored the composition of soil microbial communities associated with different types of minerals in various soil horizons. To this effect, a field experiment was set up in which mineral specimens of apatite, biotite, and oligoclase were buried in the organic, eluvial, and upper illuvial horizons of a podzol soil. After an incubation period of two years, the soil attached to the mineral surfaces was collected, and microbial communities were analyzed by means of Illumina MiSeq sequencing of the 16S (prokaryotic) and 18S (eukaryotic) ribosomal RNA genes. We found that both composition and diversity of bacterial, archaeal, and fungal communities varied across the different mineral surfaces, and that mineral type had a greater influence on structuring microbial assemblages than soil horizon. Thus, our findings emphasize the importance of mineral surfaces as ecological niches in soils.
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| 7. |
- Ahmed, Engy, et al.
(författare)
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Siderophore Production by Microorganisms Isolated From a Podzol Soil Profile
- 2015
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 32:5, s. 397-411
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Tidskriftsartikel (refereegranskat)abstract
- Siderophore-producing bacteria/actinobacteria and fungi were isolated from O- (organic), E- (eluvial), B- (upper illuvial), and C- (parent material) horizons of podzol soil. Siderophores were isolated and hydroxamate type siderophores were detected and quantitated by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry. The molecular identification of siderophore-producing isolates showed that there was a high diversity of fungal and bacterial/actinobacterial species throughout the soil profile. The isolated bacteria/actinobacteria showed different abilities in the production of ferrioxamines (E, B, G and D). Moreover, the isolated fungal species showed great variety in the production of ferrichromes, coprogens and fusarinines.
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| 8. |
- Ahmed, Engy, et al.
(författare)
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Siderophores in environmental research : roles and applications
- 2014
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Ingår i: Microbial Biotechnology. - : Wiley. - 1751-7907 .- 1751-7915. ; 7:3, s. 196-208
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Forskningsöversikt (refereegranskat)abstract
- Siderophores are organic compounds with low molecular masses that are produced by microorganisms and plants growing under low iron conditions. The primary function of these compounds is to chelate the ferric iron [Fe(III)] from different terrestrial and aquatic habitats and thereby make it available for microbial and plant cells. Siderophores have received much attention in recent years because of their potential roles and applications in various areas of environmental research. Their significance in these applications is because siderophores have the ability to bind a variety of metals in addition to iron, and they have a wide range of chemical structures and specific properties. For instance, siderophores function as biocontrols, biosensors, and bioremediation and chelation agents, in addition to their important role in weathering soil minerals and enhancing plant growth. The aim of this literature review is to outline and discuss the important roles and functions of siderophores in different environmental habitats and emphasize the significant roles that these small organic molecules could play in applied environmental processes.
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| 9. |
- Ahmed, Engy, et al.
(författare)
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The effect of soil horizon and mineral type on the distribution of siderophores in soil
- 2014
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 131, s. 184-195
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Tidskriftsartikel (refereegranskat)abstract
- Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies like production of siderophores. Siderophores are operationally defined as low-molecular-mass biogenic Fe(III)-binding compounds, that can increase the bioavailability of iron by promoting the dissolution of iron-bearing minerals. In the present study, we investigated the composition of dissolved and adsorbed siderophores of the hydroxamate family in the soil horizons of podzol and the effect of specific mineral types on siderophores. Three polished mineral specimens of 3 cm x 4 cm x 3 mm (apatite, biotite and oligioclase) were inserted in the soil horizons (O (organic), E (eluvial) and B (upper illuvial)). After two years, soil samples were collected from both the bulk soil of the whole profile and from the soil attached to the mineral surfaces. The concentration of ten different fungal tri-hydroxamates within ferrichromes, fusigen and coprogens families, and five bacterial hydroxamates within the ferrioxamine family were detected. All hydroxamate types were determined in both soil water (dissolved) and soil methanol (adsorbed) extracts along the whole soil profile by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS); hence, the study is the most extensive of its kind. We found that coprogens and fusigen were present in much higher concentrations in bulk soil than were ferrioxamines and ferrichromes. On the other hand, the presence of the polished mineral completely altered the distribution of siderophores. In addition, each mineral had a unique interaction with the dissolved and adsorbed hydroxamates in the different soil horizons. Thus siderophore composition in the soil environment is controlled by the chemical, physical and biological characteristics of each soil horizon and also by the available mineral types.
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