Change search
Link to record
Permanent link

Direct link
Ahmed, Engy
Publications (10 of 15) Show all publications
Ahmed, E., Hugerth, L. W., Logue, J. B., Brüchert, V., Andersson, A. F. & Holmström, S. J. M. (2017). Mineral Type Structures Soil Microbial Communities. Geomicrobiology Journal, 34(6), 538-545
Open this publication in new window or tab >>Mineral Type Structures Soil Microbial Communities
Show others...
2017 (English)In: Geomicrobiology Journal, ISSN 0149-0451, E-ISSN 1521-0529, Vol. 34, no 6, p. 538-545Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Apatite, biotite, microbial ecology, oligoclase, podzol
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-144613 (URN)10.1080/01490451.2016.1225868 (DOI)000401743100006 ()
Available from: 2017-06-26 Created: 2017-06-26 Last updated: 2022-02-28Bibliographically approved
Cataldi, G., Brandeker, A., Thébault, P., Singer, K., Ahmed, E., de Vries, B. L., . . . Olofsson, G. (2017). Searching for Biosignatures in Exoplanetary Impact Ejecta. Astrobiology, 17(8), 721-746
Open this publication in new window or tab >>Searching for Biosignatures in Exoplanetary Impact Ejecta
Show others...
2017 (English)In: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 17, no 8, p. 721-746Article in journal (Refereed) Published
Abstract [en]

With the number of confirmed rocky exoplanets increasing steadily, their characterization and the search for exoplanetary biospheres are becoming increasingly urgent issues in astrobiology. To date, most efforts have concentrated on the study of exoplanetary atmospheres. Instead, we aim to investigate the possibility of characterizing an exoplanet (in terms of habitability, geology, presence of life, etc.) by studying material ejected from the surface during an impact event. For a number of impact scenarios, we estimate the escaping mass and assess its subsequent collisional evolution in a circumstellar orbit, assuming a Sun-like host star. We calculate the fractional luminosity of the dust as a function of time after the impact event and study its detectability with current and future instrumentation. We consider the possibility to constrain the dust composition, giving information on the geology or the presence of a biosphere. As examples, we investigate whether calcite, silica, or ejected microorganisms could be detected. For a 20km diameter impactor, we find that the dust mass escaping the exoplanet is roughly comparable to the zodiacal dust, depending on the exoplanet's size. The collisional evolution is best modeled by considering two independent dust populations, a spalled population consisting of nonmelted ejecta evolving on timescales of millions of years, and dust recondensed from melt or vapor evolving on much shorter timescales. While the presence of dust can potentially be inferred with current telescopes, studying its composition requires advanced instrumentation not yet available. The direct detection of biological matter turns out to be extremely challenging. Despite considerable difficulties (small dust masses, noise such as exozodiacal dust, etc.), studying dusty material ejected from an exoplanetary surface might become an interesting complement to atmospheric studies in the future.

Keywords
Biosignatures, Exoplanets, Impacts, Interplanetary dust, Remote sensing
National Category
Astronomy, Astrophysics and Cosmology Biological Sciences
Identifiers
urn:nbn:se:su:diva-147126 (URN)10.1089/ast.2015.1437 (DOI)000407893800003 ()28692303 (PubMedID)
Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2022-02-28Bibliographically approved
Ahmed, E., Abdulla, H. M., Mohamed, A. H. & El-Bassuony, A. D. (2016). Remediation and recycling of chromium from tannery wastewater using combined chemical-biological treatment system. Process Safety and Environmental Protection, 104, 1-10
Open this publication in new window or tab >>Remediation and recycling of chromium from tannery wastewater using combined chemical-biological treatment system
2016 (English)In: Process Safety and Environmental Protection, ISSN 0957-5820, E-ISSN 1744-3598, Vol. 104, p. 1-10Article in journal (Refereed) Published
Abstract [en]

Tannery wastewater containing chromium (Cr) is one of the most serious problems in leather industry. In order to develop an effective and eco-friendly treatment technology, a combined chemical-biological treatment system was performed for Cr remediation and recycling. The aim of the present study is to design a laboratory scale system using chemical precipitation of Cr(III) combined with biological removal of Cr(VI) from tannery wastewater, and to investigate the possibility of recycling the recovered Cr(III) in the tanning industry. Chemical precipitation of Cr(III) was carried out using lime and cement dust. The actinomycete strain Kitasatosporia sp. was used in microcosm studies for Cr(VI) bioremoval. Moreover, parameters such as type of porous medium, inoculum size, flow rate and culture conditions were investigated. The precipitated Cr(III) that was recovered from the chemical precipitation stage was recycled in the leather tanning industry. Our findings indicate that the maximum Cr(III) precipitation (98%) was achieved using 2 g/100 mL of lime and 2 h of settling rate. On the other hand, microcosm columns using sand that was inoculated with induced culture (OD600 = 2.43) and flow rate (2 mL/min) gave the maximum recovery (99%) of Cr(VI). The experimental Cr(III) was successfully recycled in the tanning process and the experimental leathers showed comparable properties as same as the leathers tanned with commercial Cr(III). Thus, we concluded that using combined chemical-biological treatment system for Cr remediation from tanning wastewater together with recycling process for the recovered Cr(III) is a promising strategy for economic and environmental friendly tanning industry.

Keywords
Actinomycetes, Cr(VI), Cr(III), Kitasatosporia, Microcosm, Reuse
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-137734 (URN)10.1016/j.psep.2016.08.004 (DOI)000389389400001 ()
Available from: 2017-01-16 Created: 2017-01-10 Last updated: 2022-02-28Bibliographically approved
Esposito, A., Ahmed, E., Ciccazzo, S., Sikorski, J., Overmann, J., Holmström, S. J. M. & Brusetti, L. (2015). Comparison of Rock Varnish Bacterial Communities with Surrounding Non-Varnished Rock Surfaces: Taxon-Specific Analysis and Morphological Description. Microbial Ecology, 70(3), 741-750
Open this publication in new window or tab >>Comparison of Rock Varnish Bacterial Communities with Surrounding Non-Varnished Rock Surfaces: Taxon-Specific Analysis and Morphological Description
Show others...
2015 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 70, no 3, p. 741-750Article in journal (Refereed) Published
Abstract [en]

Rock varnish is a thin layer of Fe and Mn oxyhydroxides with embedded clay minerals that contain an increased Mn/Fe ratio compared to that of the Earth's crust. Even if the study of rock varnish has important implications in several fields, the composition of epilithic bacterial communities and the distribution of taxa on varnish surfaces are still not wholly described. The aim of this study was (i) to identify the bacterial taxa which show the greatest variation between varnish and non-varnish environments, collected from the same rock, and (ii) to describe the morphology of epilithic communities through scanning electron microscopy (SEM). Triplicate samples of rock surfaces with varnish and triplicate samples without varnish were collected from five sites in Matsch Valley (South Tyrol, Italy). The V4 region of 16S rRNA gene was analyzed by Illumina sequencing. Fifty-five ubiquitous taxa have been examined to assess variation between varnish and non-varnish. Cyanobacteria, Chloroflexi, Proteobacteria along with minor taxa such as Solirubrobacterales, Conexibaxter, and Rhodopila showed significant variations of abundance, diversity, or both responding to the ecology (presence/absence of varnish). Other taxa, such as the genus Edaphobacter, showed a more marked spatial variation responding to the sampling site. SEM images showed a multitude of bacterial morphologies and structures involved in the process of attachment and creation of a suitable environment for growth. The features emerging from this analysis suggest that the highly oxidative Fe and Mn-rich varnish environment favors anoxigenic autotrophy and establishment of highly specialized bacteria.

Keywords
Geomicrobiology, Rock varnish, High mountain, Epilithic bacteria, Alps
National Category
Biological Sciences Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-122254 (URN)10.1007/s00248-015-0617-4 (DOI)000361984700013 ()
Available from: 2015-11-02 Created: 2015-10-28 Last updated: 2022-02-23Bibliographically approved
Ahmed, E. (2015). Microbe-mineral interactions in soil: Investigation of biogenic chelators, microenvironments and weathering processes. (Doctoral dissertation). Stockholm: Department of Geological Sciences, Stockholm University
Open this publication in new window or tab >>Microbe-mineral interactions in soil: Investigation of biogenic chelators, microenvironments and weathering processes
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interplay between geology and biology has shaped the Earth during billions of years. Microbe-mineral interactions are prime examples of this interplay and underscore the importance of microorganisms in making Earth a suitable environment for all forms of life. The present thesis takes an interdisciplinary approach to obtain an integrated understanding of microbe-mineral interactions. More specifically it addresses how the composition and distribution of biogenic weathering agents (siderophores) differ with regard to soil horizon and mineral type in situ, what siderophore type soil microorganisms produces under laboratory conditions, what role microbial surface attachment plays in mineral weathering reactions and what central roles and applications siderophores have in the environment.

Podzol, the third most abundant soil in Europe, and most abundant in Scandinavia, was chosen for a field experiment, where three minerals (apatite, biotite and oligoclase) were inserted in the organic, eluvial and upper illuvial soil horizons. The study started with an investigation of the siderophore composition in the bulk soil profile and on the mineral surfaces (paper I), which was followed by a study of the siderophore producing capabilities of microorganisms isolated from the soil profile under laboratory conditions (paper II). Subsequently, a study was done on the impact of microbial surface attachment on biotite dissolution (paper III). Finally, the roles of siderophores in nature and their potential applications were reviewed (paper IV).

The major findings were that the concentration of hydroxamate siderophores in the soil attached to the mineral surfaces was greater than those in the surrounding bulk soil, indicating that the minerals stimulate the microbial communities attached to their surfaces to produce more siderophores than the microorganisms in the bulk soil. Each mineral had a unique assemblage of hydroxamate siderophores, that makes the mineral type one of the main factors affecting siderophore composition in the natural environment. Siderophore production varied between the microbial species originating from different soil horizons, suggesting that the metabolic properties of microbes in deep soil horizons function differently from those at upper soil horizons. Microbial surface attachment enhanced the biotite dissolution, showing that attached microbes has a greater influence on weathering reactions in soil than planktonic populations. In conclusion, our findings reflected that the complicated relationship between microorganisms and mineral surfaces reinforces the central theme of biogeochemistry that the mineral controls the biological activity in the natural environments. However, the importance of these relationships to the biogeochemical systems requires further investigation.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2015
Keywords
Podzol, Biotite, Apatite, Oligoclase, Microbial attachment, Siderophores, Soil microorganisms
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-115250 (URN)978-91-7649-135-5 (ISBN)
Public defence
2015-05-11, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In press. Paper 3: In press.

 

Available from: 2015-04-20 Created: 2015-03-18 Last updated: 2022-02-23Bibliographically approved
Ahmed, E. & Holmström, S. J. M. (2015). Microbe-mineral interactions: The impact of surface attachment on mineral weathering and element selectivity by microorganisms. Chemical Geology, 403, 13-23
Open this publication in new window or tab >>Microbe-mineral interactions: The impact of surface attachment on mineral weathering and element selectivity by microorganisms
2015 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 403, p. 13-23Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Acidification, Biotite, Bacteria, Complexation, Fungi, Siderophores
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-117771 (URN)10.1016/j.chemgeo.2015.03.009 (DOI)000353832800002 ()
Available from: 2015-06-05 Created: 2015-06-01 Last updated: 2022-02-23Bibliographically approved
Ahmed, E. & Holmström, S. J. M. (2015). Siderophore Production by Microorganisms Isolated From a Podzol Soil Profile. Geomicrobiology Journal, 32(5), 397-411
Open this publication in new window or tab >>Siderophore Production by Microorganisms Isolated From a Podzol Soil Profile
2015 (English)In: Geomicrobiology Journal, ISSN 0149-0451, E-ISSN 1521-0529, Vol. 32, no 5, p. 397-411Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
bacteria, fungi, hydroxamates
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-114824 (URN)10.1080/01490451.2014.925011 (DOI)000354619500001 ()
Available from: 2015-03-11 Created: 2015-03-11 Last updated: 2022-02-23Bibliographically approved
Schütze, E., Ahmed, E., Voit, A., Klose, M., Greyer, M., Svatoš, A., . . . Kothe, E. (2015). Siderophore production by streptomycetes-stability and alteration of ferrihydroxamates in heavy metal-contaminated soil. Environmental Science and Pollution Research, 22(24), 19376-19383
Open this publication in new window or tab >>Siderophore production by streptomycetes-stability and alteration of ferrihydroxamates in heavy metal-contaminated soil
Show others...
2015 (English)In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 22, no 24, p. 19376-19383Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Soil, Siderophores, Chelators, Ferrioxamines, Streptomycetes, Heavymetals
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-125795 (URN)10.1007/s11356-014-3842-3 (DOI)000366637300007 ()
Available from: 2016-01-25 Created: 2016-01-18 Last updated: 2022-02-23Bibliographically approved
Ahmed, E. & Holmström, S. J. M. (2014). Siderophores in environmental research: roles and applications. Microbial Biotechnology, 7(3), 196-208
Open this publication in new window or tab >>Siderophores in environmental research: roles and applications
2014 (English)In: Microbial Biotechnology, ISSN 1751-7907, E-ISSN 1751-7915, Vol. 7, no 3, p. 196-208Article, review/survey (Refereed) Published
Abstract [en]

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.

National Category
Geology
Identifiers
urn:nbn:se:su:diva-104143 (URN)10.1111/1751-7915.12117 (DOI)000333969900002 ()
Note

AuthorCount:2;

Available from: 2014-06-09 Created: 2014-06-03 Last updated: 2022-03-23Bibliographically approved
Ahmed, E. & Holmström, S. J. M. (2014). The effect of soil horizon and mineral type on the distribution of siderophores in soil. Geochimica et Cosmochimica Acta, 131, 184-195
Open this publication in new window or tab >>The effect of soil horizon and mineral type on the distribution of siderophores in soil
2014 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 131, p. 184-195Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-102946 (URN)10.1016/j.gca.2014.01.031 (DOI)000333330100013 ()
Note

AuthorCount:2;

Available from: 2014-04-30 Created: 2014-04-25 Last updated: 2022-02-23Bibliographically approved
Organisations

Search in DiVA

Show all publications