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Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching
Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). (Ctr Ecol & Evolut Microbial Model Syst EEMiS;Systems Biology of Extreme Microorganisms)ORCID-id: 0000-0003-0021-2452
University of Luxembourg, Luxembourg.
Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM). Universität Duisburg-Essen, Germany.
Università della Svizzera italiana, Switzerland;Swiss Institute of Bioinformatics (SIB), Switzerland.ORCID-id: 0000-0002-6469-0296
Vise andre og tillknytning
2018 (engelsk)Inngår i: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, artikkel-id 3059Artikkel i tidsskrift (Fagfellevurdert) 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

sted, utgiver, år, opplag, sider
Frontiers Media S.A., 2018. Vol. 9, artikkel-id 3059
Emneord [en]
redox control, microbial, bioleaching, chalcopyrite, iron oxidation, sulfobacillus, leptospirillum
HSV kategori
Forskningsprogram
Ekologi, Mikrobiologi
Identifikatorer
URN: urn:nbn:se:lnu:diva-77662DOI: 10.3389/fmicb.2018.03059ISI: 000453089800001PubMedID: 30631311Scopus ID: 2-s2.0-85058415510OAI: oai:DiVA.org:lnu-77662DiVA, id: diva2:1246967
Tilgjengelig fra: 2018-09-10 Laget: 2018-09-10 Sist oppdatert: 2019-08-29bibliografisk kontrollert
Inngår i avhandling
1. Function and Adaptation of Acidophiles in Natural and Applied Communities
Åpne denne publikasjonen i ny fane eller vindu >>Function and Adaptation of Acidophiles in Natural and Applied Communities
2018 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Växjö: Linnaeus University Press, 2018
Serie
Linnaeus University Dissertations ; 328
Emneord
Acidophiles, Biomining, Psychrophiles, Adaptation, Acid Sulfate Soil, Redox Control
HSV kategori
Forskningsprogram
Naturvetenskap, Ekologi
Identifikatorer
urn:nbn:se:lnu:diva-77666 (URN)978-91-88761-94-1 (ISBN)978-91-88761-95-8 (ISBN)
Disputas
2018-10-19, Norrgård, Kalmar, 09:30 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2018-09-11 Laget: 2018-09-10 Sist oppdatert: 2018-11-16bibliografisk kontrollert

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