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See detailWeak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching
Christel, Stephan; Herold, Malte UL; Bellenberg, Sören et al

in Frontiers in Microbiology (2018), 9(December), 1-12

Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidic ores that provides a more environmentally friendly alternative to many traditional metal extraction ... [more ▼]

Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidic ores that provides a more environmentally friendly alternative to many traditional metal extraction methods, such as roasting or smelting. Industrial interest is steadily increasing and today, circa 15–20% of the world’s copper production can be traced back to this method. However, bioleaching of the world’s most abundant copper mineral chalcopyrite suffers from low dissolution rates, often attributed 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 low oxidation/reduction potential (ORP), but chemical redox control in bioleaching heaps is difficult and costly. As an alternative, selected weak iron-oxidizers could be employed that are incapable of scavenging exceedingly low concentrations of iron and therefore, raise the ORP just above the onset of bioleaching, but not high enough to allow for the occurrence of passivation. In this study, we report that microbial iron oxidation by Sulfobacillus thermosulfidooxidans meets these specifications. Chalcopyrite concentrate bioleaching experiments with S. thermosulfidooxidans as the sole iron oxidizer exhibited significantly lower redox potentials and higher release of copper compared to communities containing the strong iron oxidizer Leptospirillum ferriphilum. Transcriptomic response to single and co-culture of these two iron oxidizers was studied and revealed a greatly decreased number of mRNA transcripts ascribed to iron oxidation in S. thermosulfidooxidans when cultured in the presence of L. ferriphilum. This allowed for the identification of genes potentially responsible for S. thermosulfidooxidans’ weaker iron oxidation to be studied in the future, as well as underlined the need for new mechanisms to control the microbial population in bioleaching heaps. [less ▲]

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See detailMulti-omics reveal the lifestyle of the acidophilic, mineral-oxidizing model species Leptospirillum ferriphilum(T).
Christel, Stephan; Herold, Malte UL; Bellenberg, Soren et al

in Applied and environmental microbiology (2017)

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 ... [more ▼]

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 ferriphilum(T) applies to survive and compete in its niche. This study presents a complete, circular genome of Leptospirillum ferriphilum(T) 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 ferriphilum(T) 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.IMPORTANCELeptospirillum ferriphilum is one of the most important iron-oxidizers in the context of acidic and metal rich environments during moderately thermophilic biomining. A high-quality circular genome of Leptospirillum ferriphilum(T) coupled with functional omics data provides new insights into its metabolic properties, such as the novel identification of genes for atmospheric nitrogen fixation, and represents an essential step for further accurate proteomic and transcriptomic investigation of this acidophile model species in the future. Additionally, light is shed on Leptospirillum ferriphilum(T) adaptation strategies to growth on the copper mineral chalcopyrite. This data can be applied to deepen our understanding and optimization of bioleaching and biooxidation, techniques that present sustainable and environmentally friendly alternatives to many traditional methods for metal extraction. [less ▲]

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See detailSystems Biology of Acidophile Biofilms for Efficient Metal Extraction
Christel, Stephan; Dopson, Mark; Vera, Mario et al

in Advanced Materials Research (2015), 1130

This European Union ERASysApp funded study will investigate one of the major drawbacks of bioleaching of the copper containing mineral chalcopyrite, namely the long lag phase between construction and ... [more ▼]

This European Union ERASysApp funded study will investigate one of the major drawbacks of bioleaching of the copper containing mineral chalcopyrite, namely the long lag phase between construction and inoculation of bioleaching heaps and the release of dissolved metals. In practice, this lag phase can be up to three years and the long time period adds to the operating expenses of bioheaps for chalcopyrite dissolution. One of the major time determining factors in bioleaching heaps is suggested to be the speed of mineral colonization by the acidophilic microorganisms present. By applying confocal microscopy, metatranscriptomics, metaproteomics, bioinformatics, and computer modeling the authors aim to investigate the processes leading up to, and influencing the attachment of three moderately thermophilic sulfur-and/or iron-oxidizing model species: Acidithiobacillus caldus, Leptospirillum ferriphilum, and Sulfobacillus thermosulfidooxidans. Stirred tank reactors containing chalcopyrite concentrate will be inoculated with these species in various orders and proportions and the effects on the lag phase and rates of metal release will be compared. Meanwhile, confocal microscopy studies of cell attachment to chalcopyrite mineral particles, as well as metatranscriptomics and metaproteomics of the formed biofilms will further increase understanding of the attachment process and help develop a model thereof. By fulfilling our goal to decrease the length of the lag phase of chalcopyrite bioleaching heaps we hope to increase their economic feasibility and therefore, industrial interest in bioleaching as a sustainable technology. [less ▲]

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