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Christel, S., Yu, C., Wu, X., Josefsson, S., Lillhonga, T., Högfors-Rönnholm, E., . . . Dopson, M. (2019). Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments [Letter to the editor]. Research in Microbiology, 170(6-7), 288-295
Open this publication in new window or tab >>Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments
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2019 (English)In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 170, no 6-7, p. 288-295Article in journal, Letter (Refereed) Published
Abstract [en]

Due to land uplift after the last ice age, previously stable Baltic Sea sulfidic sediments are becoming dry land. When these sediments are drained, the sulfide minerals are exposed to air and can release large amounts of metals and acid into the environment. This can cause severe ecological damage such as fish kills in rivers feeding the northern Baltic Sea. In this study, five sites were investigated for the occurrence of acid sulfate soils and their geochemistry and microbiology was identified. The pH and soil chemistry identified three of the areas as having classical acid sulfate soil characteristics and culture independent identification of 16S rRNA genes identified populations related to acidophilic bacteria capable of catalyzing sulfidic mineral dissolution, including species likely adapted to low temperature. These results were compared to an acid sulfate soil area that had been flooded for ten years and showed that the previously oxidized sulfidic materials had an increased pH compared to the unremediated oxidizied layers. In addition, the microbiology of the flooded soil had changed such that alkalinity producing ferric and sulfate reducing reactions had likely occurred. This suggested that flooding of acid sulfate soils mitigates their environmental impact.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
sulfide mineral; metal; sulfur; 16S rRNA gene; mitigation; wetland
National Category
Microbiology Earth and Related Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-77664 (URN)10.1016/j.resmic.2019.06.002 (DOI)000491121700006 ()
Available from: 2018-09-10 Created: 2018-09-10 Last updated: 2019-10-31Bibliographically approved
Buetti-Dinh, A., Galli, V., Bellenberg, S., Ilie, O., Herold, M., Christel, S., . . . Dopson, M. (2019). Deep neural networks outperform human expert's capacity in characterizing bioleaching bacterial biofilm composition. Biotechnology Reports, 22, 1-5, Article ID e00321.
Open this publication in new window or tab >>Deep neural networks outperform human expert's capacity in characterizing bioleaching bacterial biofilm composition
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2019 (English)In: Biotechnology Reports, ISSN 0156-1383, E-ISSN 2215-017X, Vol. 22, p. 1-5, article id e00321Article in journal (Refereed) Published
Abstract [en]

Background: Deep neural networks have been successfully applied to diverse fields of computer vision. However, they only outperform human capacities in a few cases. Methods: The ability of deep neural networks versus human experts to classify microscopy images was tested on biofilm colonization patterns formed on sulfide minerals composed of up to three different bioleaching bacterial species attached to chalcopyrite sample particles. Results: A low number of microscopy images per category (<600) was sufficient for highly efficient computational analysis of the biofilm's bacterial composition. The use of deep neural networks reached an accuracy of classification of ∼90% compared to ∼50% for human experts. Conclusions: Deep neural networks outperform human experts’ capacity in characterizing bacterial biofilm composition involved in the degradation of chalcopyrite. This approach provides an alternative to standard, time-consuming biochemical methods. © 2019 The Author

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Acidophiles, Bacterial biofilm, Biomining, Convolutional neural networks, Deep learning, Microscopy imaging, sulfide, Acidithiobacillus caldus, Article, artificial neural network, bacterium, bacterium culture, biofilm, bioleaching, epifluorescence microscopy, high throughput screening, image analysis, Leptospirillum ferriphilum, microbial colonization, microscopy, nonhuman, performance, priority journal, Sulfobacillus thermosulfidooxidans, training
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-86412 (URN)10.1016/j.btre.2019.e00321 (DOI)2-s2.0-85063054023 (Scopus ID)
Available from: 2019-07-11 Created: 2019-07-11 Last updated: 2019-10-11Bibliographically approved
Hogfors-Ronnholm, E., Lopez-Fernandez, M., Christel, S., Brambilla, D., Huntemann, M., Clum, A., . . . Dopson, M. (2019). Metagenomes and metatranscriptomes from boreal potential and actual acid sulfate soil materials. Scientific Data, 6, 1-6, Article ID 207.
Open this publication in new window or tab >>Metagenomes and metatranscriptomes from boreal potential and actual acid sulfate soil materials
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2019 (English)In: Scientific Data, E-ISSN 2052-4463, Vol. 6, p. 1-6, article id 207Article in journal (Refereed) Published
Abstract [en]

Natural sulfide rich deposits are common in coastal areas worldwide, including along the Baltic Sea coast. When artificial drainage exposes these deposits to atmospheric oxygen, iron sulfide minerals in the soils are rapidly oxidized. This process turns the potential acid sulfate soils into actual acid sulfate soils and mobilizes large quantities of acidity and leachable toxic metals that cause severe environmental problems. It is known that acidophilic microorganisms living in acid sulfate soils catalyze iron sulfide mineral oxidation. However, only a few studies regarding these communities have been published. In this study, we sampled the oxidized actual acid sulfate soil, the transition zone where oxidation is actively taking place, and the deepest un-oxidized potential acid sulfate soil. Nucleic acids were extracted and 16S rRNA gene amplicons, metagenomes, and metatranscriptomes generated to gain a detailed insight into the communities and their activities. The project will be of great use to microbiologists, environmental biologists, geochemists, and geologists as there is hydrological and geochemical monitoring from the site stretching back for many years.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-89865 (URN)10.1038/s41597-019-0222-3 (DOI)000490560100003 ()31619684 (PubMedID)
Available from: 2019-10-31 Created: 2019-10-31 Last updated: 2019-10-31Bibliographically approved
Bellenberg, S., Buetti-Dinh, A., Galli, V., Ilie, O., Herold, M., Christel, S., . . . Dopson, M. (2018). Automated Microscopic Analysis of Metal Sulfide Colonization by Acidophilic Microorganisms. Applied and Environmental Microbiology, 84(20), Article ID UNSP e01835-18.
Open this publication in new window or tab >>Automated Microscopic Analysis of Metal Sulfide Colonization by Acidophilic Microorganisms
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2018 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 84, no 20, article id UNSP e01835-18Article in journal (Refereed) Published
Abstract [en]

Industrial biomining processes are currently focused on metal sulfides and their dissolution, which is catalyzed by acidophilic iron(II)- and/or sulfur-oxidizing microorganisms. Cell attachment on metal sulfides is important for this process. Biofilm formation is necessary for seeding and persistence of the active microbial community in industrial biomining heaps and tank reactors, and it enhances metal release. In this study, we used a method for direct quantification of the mineral-attached cell population on pyrite or chalcopyrite particles in bioleaching experiments by coupling high-throughput, automated epifluorescence microscopy imaging of mineral particles with algorithms for image analysis and cell quantification, thus avoiding human bias in cell counting. The method was validated by quantifying cell attachment on pyrite and chalcopyrite surfaces with axenic cultures of Acidithiobacillus caldus, Leptospirillum ferriphilum, and Sulfobacillus thermosulfidooxidans. The method confirmed the high affinity of L. ferriphilum cells to colonize pyrite and chalcopyrite surfaces and indicated that biofilm dispersal occurs in mature pyrite batch cultures of this species. Deep neural networks were also applied to analyze biofilms of different microbial consortia. Recent analysis of the L. ferriphilum genome revealed the presence of a diffusible soluble factor (DSF) family quorum sensing system. The respective signal compounds are known as biofilm dispersal agents. Biofilm dispersal was confirmed to occur in batch cultures of L. ferriphilum and S. thermosulfidooxidans upon the addition of DSF family signal compounds. IMPORTANCE The presented method for the assessment of mineral colonization allows accurate relative comparisons of the microbial colonization of metal sulfide concentrate particles in a time-resolved manner. Quantitative assessment of the mineral colonization development is important for the compilation of improved mathematical models for metal sulfide dissolution. In addition, deep-learning algorithms proved that axenic or mixed cultures of the three species exhibited characteristic biofilm patterns and predicted the biofilm species composition. The method may be extended to the assessment of microbial colonization on other solid particles and may serve in the optimization of bioleaching processes in laboratory scale experiments with industrially relevant metal sulfide concentrates. Furthermore, the method was used to demonstrate that DSF quorum sensing signals directly influence colonization and dissolution of metal sulfides by mineral-oxidizing bacteria, such as L. ferriphilum and S. thermosulfidooxidans.

Place, publisher, year, edition, pages
American society for microbiology, 2018
Keywords
bioleaching, biofilm formation, biofilm dispersal, image analysis, microbe-mineral interaction, quorum sensing, diffusible soluble factor, biofilms, fluorescent image analysis, microbe-mineral interactions
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-78464 (URN)10.1128/AEM.01835-18 (DOI)000446206900020 ()30076195 (PubMedID)2-s2.0-85054103905 (Scopus ID)
Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2019-08-29Bibliographically approved
Högfors-Rönnholm, E., Christel, S., Dalhem, K., Lillhonga, T., Engblom, S., Österholm, P. & Dopson, M. (2018). Chemical and microbiological evaluation of novel chemical treatment methods for acid sulfate soils. Science of the Total Environment, 625, 39-49
Open this publication in new window or tab >>Chemical and microbiological evaluation of novel chemical treatment methods for acid sulfate soils
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2018 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 625, p. 39-49Article in journal (Refereed) Published
Abstract [en]

Naturally occurring sulfide rich deposits are common along the northern Baltic Sea coast thatwhen exposed to air, release large amounts of acid and metals into receiving water bodies. This causes severe environmental implications for agriculture, forestry, and building of infrastructure. In this study, we investigated the efficiency of ultrafine-grained calcium carbonate and peat (both separately and in combination) to mitigate acid and metal release. The experiments were carried out aerobically that mimicked summer conditions when the groundwater level is low and acid sulfate soils are exposed to oxygen, and anaerobically that is similar to autumn to spring conditions. The ultrafine-grained calcium carbonate dissipated well in the soil and its effect alone and when mixed with peat raised the pH and reduced pyrite dissolution while peat alone was similar to the controls and did not halt metal and acid release. High throughput 16S rRNA gene sequencing identified populations most similar to characterized acidophiles in the control and peat treated incubations while the acidophilic like populations were altered in the calcium carbonate alone and calcium carbonate plus peat treated acid sulfate soils. Coupled with the geochemistry data, it was suggested that the acidophiles were inactivated by the high pH in the presence of calcium carbonate but catalyzed pyrite dissolution in the controls and peat incubations. In conclusion, the anaerobic conditions during winter would likely be sufficient to mitigate acid production and metal release from acid sulfate soils and in the summer, treatment with calcium carbonate was the best mitigation method. (c) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Mitigation, Pyrite, Iron, 16S rRNA, Compositional PCA
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-71751 (URN)10.1016/j.scitotenv.2017.12.287 (DOI)000426356600005 ()29287211 (PubMedID)2-s2.0-85039173598 (Scopus ID)
Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2019-08-29Bibliographically approved
Christel, S. (2018). Function and Adaptation of Acidophiles in Natural and Applied Communities. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Function and Adaptation of Acidophiles in Natural and Applied Communities
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Acidophiles are organisms that have evolved to grow optimally at high concentrations of protons. Members of this group are found in all three domains of life, although most of them belong to the Archaea and Bacteria. As their energy demand is often met chemolithotrophically by the oxidation of basic ions and molecules such as Fe2+, H2, and sulfur compounds, they are often found in environments marked by the natural or anthropogenic exposure of sulfide minerals. Nonetheless, organoheterotrophic growth is also common, especially at higher temperatures. Beside their remarkable resistance to proton attack, acidophiles are resistant to a multitude of other environmental factors, including toxic heavy metals, high temperatures, and oxidative stress. This allows them to thrive in environments with high metal concentrations and makes them ideal for application in so-called biomining technologies.

The first study of this thesis investigated the iron-oxidizer Acidithiobacillus ferrivorans that is highly relevant for boreal biomining. Several unresolved nodes of its sulfur metabolism were elucidated with the help of RNA transcript sequencing analysis. A model was proposed for the oxidation of the inorganic sulfur compound tetrathionate. In a second paper, this species’ transcriptional response to growth at low temperature was explored and revealed that At. ferrivorans increases expression of only very few known cold-stress genes, underlining its strong adaptation to cold environments.

Another set of studies focused on the environmentally friendly metal winning technology of bioleaching. One of the most important iron-oxidizers in many biomining operations is Leptospirillum ferriphilum. Despite its significance, only a draft genome sequence was available for its type strain.Therefore, in the third paper of this thesis we published a high quality, closed genome sequence of this strain for future use as a reference, revealing a previously unidentified nitrogen fixation system and improving annotation of genes relevant in biomining environments. In addition, RNA transcript and protein patterns during L. ferriphilum’s growth on ferrous iron and in bioleaching culture were used to identify key traits that aid its survival in extremely acidic, metal-rich environments. The biomining of copper from chalcopyrite is plagued by a slow dissolution rate, which can reportedly be circumvented by low redox potentials. As conventional redox control is impossible in heap leaching, paper four explored the possibility of using differentially efficient iron oxidizers to influence this parameter. The facultative heterotrophic Sulfobacillus thermosulfidooxidans was identified as maintaining a redox potential of ~550 mV vs Ag/AgCl, favorable for chalcopyrite dissolution,while L. ferriphilum caused the potential to raise far above this critical value. RNA transcript analysis was used to identify genomic features that may contribute to this behavior.

Lastly, six fields in Northern Sweden were examined for the presence of acid sulfate soils in the fifth paper. The study revealed three acid sulfate soils. The presence of acidophiles that likely catalyze the production of acid in the soil was confirmed by community 16S gene amplicon analysis. One site that was flooded in a remediation attempt and is therefore anoxic still exhibited similar bacteria, however, these now likely grow via ferric iron reduction. This process consumes protons and could explain the observed rise in pH at this site.

This thesis examines acidophiles in pure culture, as well as natural and designed communities. Key metabolic traits involved in the adaptation to their habitats were elucidated, and their application in mining operations was discussed. Special attention was paid to acidophiles in chalcopyrite bioleaching and in cold environments, including environmental acid sulfate soils in Northern Sweden.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2018
Series
Linnaeus University Dissertations ; 328
Keywords
Acidophiles, Biomining, Psychrophiles, Adaptation, Acid Sulfate Soil, Redox Control
National Category
Ecology
Research subject
Natural Science, Ecology
Identifiers
urn:nbn:se:lnu:diva-77666 (URN)978-91-88761-94-1 (ISBN)978-91-88761-95-8 (ISBN)
Public defence
2018-10-19, Norrgård, Kalmar, 09:30 (English)
Opponent
Supervisors
Available from: 2018-09-11 Created: 2018-09-10 Last updated: 2018-11-16Bibliographically approved
Berkelmann, D., Schneider, D., Engelhaupt, M., Heinemann, M., Christel, S., Wijayanti, M., . . . Daniel, R. (2018). How Rainforest Conversion to Agricultural Systems in Sumatra (Indonesia) Affects Active Soil Bacterial Communities. Frontiers in Microbiology, 9, Article ID 2381.
Open this publication in new window or tab >>How Rainforest Conversion to Agricultural Systems in Sumatra (Indonesia) Affects Active Soil Bacterial Communities
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2018 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 2381Article in journal (Refereed) Published
Abstract [en]

Palm oil production in Indonesia increased constantly over the last decades, which led to massive deforestation, especially on Sumatra island. The ongoing conversion of rainforest to agricultural systems results in high biodiversity loss. Here, we present the first RNA-based study on the effects of rainforest transformation to rubber and oil palm plantations in Indonesia for the active soil bacterial communities. For this purpose, bacterial communities of three different converted systems (jungle rubber, rubber plantation, and oil palm plantation) were studied in two landscapes with rainforest as reference by RT-PCR amplicon-based analysis of 16S rRNA gene transcripts. Active soil bacterial communities were dominated by Frankiales (Actinobacteria), subgroup 2 of the Acidobacteria and Alphaproteobacteria (mainly Rhizobiales and Rhodospirillales). Community composition differed significantly between the converted land use systems and rainforest reference sites. Alphaproteobactena decreased significantly in oil palm samples compared to rainforest samples. In contrast, relative abundances of taxa within the Acidobacteria increased. Most important abiotic drivers for shaping soil bacterial communities were pH, calcium concentration, base saturation and C:N ratio. Indicator species analysis showed distinct association patterns for the analyzed land use systems. Nitrogen-fixing taxa including members of Rhizobiales and Rhodospirillales were associated with rainforest soils while nitrifiers and heat-resistant taxa including members of Actinobacteria were associated with oil palm soils. Predicted metabolic profiles revealed that the relative abundances of genes associated with fixation of nitrogen significantly decreased in plantation soils. Furthermore, predicted gene abundances regarding motility, competition or gene transfer ability indicated rainforest conversion-induced changes as well.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
16S rRNA gene transcripts, soil bacterial communities, rainforest conversion, active bacterial communities, oil palm plantation, Sumatra
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-78460 (URN)10.3389/fmicb.2018.02381 (DOI)000446867700001 ()2-s2.0-85055196936 (Scopus ID)
Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2019-08-29Bibliographically approved
Högfors-Rönnholm, E., Christel, S., Engblom, S. & Dopson, M. (2018). Indirect DNA extraction method suitable for acidic soil with high clay content. MethodsX, 5, 136-140
Open this publication in new window or tab >>Indirect DNA extraction method suitable for acidic soil with high clay content
2018 (English)In: MethodsX, ISSN 1258-780X, E-ISSN 2215-0161, Vol. 5, p. 136-140Article in journal (Refereed) Published
Abstract [en]

DNA extraction is an essential procedure when investigating microbial communities in environmental samples by sequencing technologies. High clay soils can be problematic as DNA adsorbs to the clay particles and can thereby be preserved from lysed, non-viable cells for a substantial period of time. In order to accurately estimate the intact and living microbial community in the soil, extracellular DNA from dead, remnant bacterial cells needs to be removed prior to DNA extraction. One possibility is to use a sodium phosphate buffer to release both extracellular DNA and bacterial cells from the clay particles. After removing the extracellular DNA by centrifugation, the remaining viable cells can be harvested and DNA extracted. The described method is a modification of a procedure for separating extracellular DNA and bacterial cells from acidic clay soils. The modified method increases bacterial cell yields from acidic clay soils, such as acid sulfate soil. The modified method eliminates some steps from the original method, as only DNA from intact bacterial cells is required. The indirect DNA extraction method increases the workload compared to standard direct extraction methods, but subsequent downstream analyses will give a more representative picture of the viable microbial community composition in the soil.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Indirect DNA extraction, Microbial community, Extracellular DNA, Acid sulfate soil, 16S rRNA gene
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-75534 (URN)10.1016/j.mex.2018.02.005 (DOI)000454531500016 ()30622912 (PubMedID)2-s2.0-85042686880 (Scopus ID)
Available from: 2018-06-11 Created: 2018-06-11 Last updated: 2019-08-29Bibliographically approved
Christel, S., Herold, M., Bellenberg, S., El Hajjami, M., Buetti-Dinh, A., Pivkine, I. V., . . . Dopson, M. (2018). Multi-omics reveal the lifestyle of the acidophilic, mineral-oxidizing model species Leptospirillum ferriphilumT. Applied and Environmental Microbiology, 4(3), Article ID UNSP e02091-17.
Open this publication in new window or tab >>Multi-omics reveal the lifestyle of the acidophilic, mineral-oxidizing model species Leptospirillum ferriphilumT
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2018 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 4, no 3, article id UNSP e02091-17Article in journal (Refereed) Published
Abstract [en]

Leptospirillum ferriphilum plays a major role in acidic, metal rich environments where it represents one of the most prevalent iron oxidizers. These milieus include acid rock and mine drainage as well as biomining operations. Despite its perceived importance, no complete genome sequence of this model species' type strain is available, limiting the possibilities to investigate the strategies and adaptations Leptospirillum ferriphilumT applies to survive and compete in its niche. This study presents a complete, circular genome of Leptospirillum ferriphilumT DSM 14647 obtained by PacBio SMRT long read sequencing for use as a high quality reference. Analysis of the functionally annotated genome, mRNA transcripts, and protein concentrations revealed a previously undiscovered nitrogenase cluster for atmospheric nitrogen fixation and elucidated metabolic systems taking part in energy conservation, carbon fixation, pH homeostasis, heavy metal tolerance, oxidative stress response, chemotaxis and motility, quorum sensing, and biofilm formation. Additionally, mRNA transcript counts and protein concentrations were compared between cells grown in continuous culture using ferrous iron as substrate and bioleaching cultures containing chalcopyrite (CuFeS2). Leptospirillum ferriphilumT adaptations to growth on chalcopyrite included a possibly enhanced production of reducing power, reduced carbon dioxide fixation, as well as elevated RNA transcripts and proteins involved in heavy metal resistance, with special emphasis on copper efflux systems. Finally, expression and translation of genes responsible for chemotaxis and motility were enhanced.

Place, publisher, year, edition, pages
American society for microbiology, 2018
National Category
Microbiology
Research subject
Ecology, Microbiology; Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-69199 (URN)10.1128/AEM.02091-17 (DOI)000423770000018 ()2-s2.0-85040673185 (Scopus ID)
Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2019-08-29Bibliographically approved
Christel, S., Herold, M., Bellenberg, S., Buetti-Dinh, A., El Hajjami, M., Pivkin, I., . . . Dopson, M. (2018). Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching. Frontiers in Microbiology, 9, Article ID 3059.
Open this publication in new window or tab >>Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching
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2018 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 3059Article in journal (Refereed) Published
Abstract [en]

Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidicores that provides a more environmentally friendly alternative to many traditional metal extractionmethods, such as roasting or smelting. Industrial interest increases steadily and today, circa 15-20%of the world’s copper production can be traced back to this method. However, bioleaching of theworld’s most abundant copper mineral chalcopyrite suffers from low dissolution rates, oftenattributed to passivating layers, which need to be overcome to use this technology to its full potential.To prevent these passivating layers from forming, leaching needs to occur at a lowoxidation/reduction potential (ORP), but chemical redox control in bioleaching heaps is difficult andcostly. As an alternative, selected weak iron-oxidizers could be employed that are incapable ofscavenging exceedingly low concentrations of iron and therefore, raise the ORP just above the onsetof bioleaching, but not high enough to allow for the occurrence of passivation. In this study, wereport that microbial iron oxidation by Sulfobacillus thermosulfidooxidans meets these specifications.Chalcopyrite concentrate bioleaching experiments with S. thermosulfidooxidans as the sole ironoxidizer exhibited significantly lower redox potentials and higher release of copper compared tocommunities containing the strong iron oxidizer Leptospirillum ferriphilum. Transcriptomic responseto single and co-culture of these two iron oxidizers was studied and revealed a greatly decreasednumber of mRNA transcripts ascribed to iron oxidation in S. thermosulfidooxidans when cultured inthe presence of L. ferriphilum. This allowed for the identification of genes potentially responsible forS. thermosulfidooxidans’ weaker iron oxidation to be studied in the future, as well as underlined theneed for mechanisms to control the microbial population in bioleaching heaps

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
redox control, microbial, bioleaching, chalcopyrite, iron oxidation, sulfobacillus, leptospirillum
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-77662 (URN)10.3389/fmicb.2018.03059 (DOI)000453089800001 ()30631311 (PubMedID)2-s2.0-85058415510 (Scopus ID)
Available from: 2018-09-10 Created: 2018-09-10 Last updated: 2019-08-29Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0021-2452

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