Solid State Phenomena Vol. 262

Abstract: The development of effective and ecofriendly processes for the recovery of critical elements poses a challenge for scientists all over the world. A novel approach is the generation of highly specific peptides that bind with high affinity to individual elements of interest. The peptides are selected by phage surface display (PSD) technology. In this study, PSD technology has been applied in two different approaches. The focus of the first approach was the identification of peptides that bind specifically to special particles of interest that are part of electronic scrap aiming towards the development of new recycling processes. In the second approach, metal ion binding peptides were isolated via PSD to use them for the targeted removal and enrichment of these elements from complex leaching solutions or from industrial waters. To address the economic production of peptides, the development of a new expression system is also part of this study.

Abstract: Phage display for discovery of specific binding peptides is nowadays widely used in the pharmaceutical industry and in many biotechnological applications. Using state-of-the-art cloning techniques we developed an easy-to-use cloning and expression system, allowing the fast production of identified peptides while avoiding proteolysis.

Abstract: Anionic ion species occur in gangue minerals and impact the bioleaching efficiency even at low concentrations. Recently, the detrimental influence of fluoride ions on bioleaching microorganisms has caused great attention in research. However, the tolerance mechanisms of bioleaching microorganisms for fluoride are still unclear. In order to reveal fluoride tolerance, culture experiments with different concentrations of fluoride and ferrous iron-grown Acidithiobacillus ferrooxidans were carried out. The results showed that oxidation-reduction potential, oxidation capacity of iron and cell density were all negatively correlated to the fluoride concentration. The growth of A. ferrooxidans showed a longer delayed time and a slower growth rate when fluoride concentration increased. The fluoride tolerance for A. ferrooxidans could be attributed to the generated ferric ions from ferrous oxidation. Ferric ions reacted with HF to decrease the concentration of F^- and finally reduced the toxicity of fluoride on A. ferrooxidans.

Abstract: The potential role of microorganisms in the in-situ recovery (ISR) of technology metals, in particular from reduced ores, is not well understood, but attracts increasing interest worldwide. Based on the feasibility criteria for ISR applications in general, effects of biota on kinetic rates of leaching are systematized. The indirect catalysis of leaching by microbial (re-)oxidation of Fe²⁺ to Fe³⁺ as directly acting e^- acceptor is a well verified mechanism, however, for practical applications this requires the availability of an oxidant in the leachant. The ex-situ bio-oxidation of Fe in an aerated bioreactor is considered as an alternative. Reactive transport simulations of ISR from sulfidic Cu ores based on kinetic rates as function of pH and oxidation potential (concentration of e^- acceptors) in comparison with thermodynamically driven metal dissolution (constrained by oxidation potential) demonstrate the key parameters for (bio-)leaching productivity.

Abstract: The sulfur activation by extracellular proteins is considered as the crucial stage during biooxidation of elemental sulfur (S⁰). In order to study genes encoding sulfur-activation related extracellular proteins of extremely thermophilic Acidianus manzaensis, the extracellular proteins with higher abundance for the strain grown on S⁰ allotropes than that on Fe²⁺ were first screened by two-dimensional gel electrophoresis, and then identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Nine genes amplified with PCR were satisfactory according to their agarose gel electrophoresis. The differential expression of these nine genes when the strain grown on S⁰ allotropes and Fe²⁺ were analyzed with real-time quantitative PCR (RT-qPCR). Results showed that seven of them were higher expressed when the strain grown on S⁰ allotropes than on Fe²⁺, indicating they may be related with sulfur activation by A. manzaensis.

Abstract: Adaption to the energy substrates and heavy metals by bioleaching micoorganisms is the prerequisite for efficient microbe-mineral interaction in bioleaching process. It is known extracellular polymer substances (EPSs) take important role in mediating the adaption to and action on energy substrates and heavy metals. This report presents the evolution of compositions and contents of the major components of EPSs of the typical bioleaching microorganisms (Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, Sulfobacillus thermosulfidooxidans, and Acidianus manzaensis,) exposed to different energy substrates and heavy metal ions. These strains were acclimated firstly to Fe²⁺ substrate, and then on the substrates elemental sulfur (S⁰), pyrite and chalcopyrite, respectively. It was found that the major components of capsule and slime EPSs in terms of proteins, polysaccharides, as well as uronic acids were quite different in contents for the Fe²⁺-acclimated strains, and they even changed more when the Fe²⁺-acclimated strains were further acclimated to the other substrates. When exposed to heavy metals, all strains demonstrated much decrease in contents of capsule EPSs, and much increase in slime EPSs contents and the heavy metals were found to bound to the slime parts. It was for the first time the EPSs of the bioleaching strains were fractionated into capsule part and slime part, and it was also for the first time we found the differences in evolution of compositions and contents of the major organic components as well as the inorganic matter of capsule EPSs and slime EPSs when the bioleaching strains were exposed to different energy substrates and heavy metals.

Abstract: Resistance of microorganisms predominating in biohydrometallurgical processes including bacteria of the genus Sulfobaсillus and archaea of the genus Acidiplasma to ferric iron ions was studied. Capabilities of the strains for growth and ferrous iron oxidation in the media containing high concentrations of ferric iron ions (of 250 to 1000 mM) were evaluated. Ferric iron ions significantly inhibited oxidative activity and growth of the studied microorganisms. It was revealed that bacteria of the genus Sulfobacillus were not able to oxidize ferrous iron actively when ferric iron concentration exceeded 500 mM, whereas archaea of the genus Acidiplasma completely oxidized ferrous iron in the medium containing 1000 mM of Fe³⁺. Growth of the microorganisms was inhibited by relatively low concentrations of ferric iron. Microorganisms did not grow in the medium containing more than 750 mM of Fe³⁺ and cells of all studied strains lysed in presence of high concentrations of ferric iron. It was shown, that archaea of the genus Acidiplasma of the family Ferroplasmaceae were more resistant to high concentrations of ferric iron than bacteria of the genus Sulfobacillus. The results obtained are important for understanding of the regularities of the formation of microbial communities performing technological processes.

Abstract: The presence of extracellular polymeric substances (EPS) and their relevance for biofilm formation on the mineral surface for a variety of microbial species play a fundamental role in the degradation of sulfide ores. EPS production is associated with induction or auto induction mechanisms as a response of bacteria to environmental conditions. In this study, we tested galactose as an inducer of EPS production in planktonic cells of Acidithiobacillus thiooxidans DSM 14887^T and their adherence to polymetallic mineral surfaces. Cells of At. thiooxidans were first adapted to grow at different concentrations of galactose (0.15, 0.25, 0.35%) using a modified 9K liquid medium and elemental sulfur as the energy source. In order to determine EPS production, the microorganisms were grown for 24 hours at different concentrations of galactose. Our results showed a cell adherence of 84% cells within 4 hours in presence of 0.15% galactose compared to 70% without galactose. The optimal concentration of galactose for maximal EPS production was 0.25% and for the attachment of cells it was 0.15%. Higher galactose concentrations inhibited microbial growth and decreased the number of cells attached to the mineral. While with a small amount of galactose in the culture media can shift the balance between sessile cells and planktonic cells, generating an increase in adhesion and therefore a possible increase of the bioleaching rate.

Abstract: The response to elevated ferrous iron concentrations was investigated in the acidophilic iron oxidizer “Ferrovum” sp. JA12 at transcriptome level. Detoxification of reactive oxygen species appears to be the most important strategy to cope with oxidative stress. The proposed iron oxidation model in “Ferrovum” spp. was supported by the transcriptome data of “Ferrovum” sp. JA12. Several gene candidates of the iron oxidation model are organized in a gene cluster conserved in iron oxidizing betaproteobacteria and zetaproteobacteria possibly indicating a common origin of iron oxidation.

Abstract: The mineral surface chemistry characterization is essential to describe the dissolution kinetics in leaching and bioleaching. Five different methods, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, have been applied to study the surface chemistry changes during pyrite, sphalerite and molybdenite bioleaching. The surface characterizations have been done for samples before and after biological and chemical leaching. The SEM images illustrated that the minerals surfaces were smooth before processing, while they covered with an ash layer after biological treatment. Although EDS analysis and Raman spectrum demonstrated the potassium jarosite formation on the pyrite surface during bioleaching, the formation of jarosite layer did not occur on the sphalerite surfaces during bioleaching. On the other hand, a sulfur layer formation on the sphalerite surface was confirmed by mentioned characterization methods. Finally, according to the XRD and EDS spectrum the molybdenite surface had been covered both with sulfur and jarosite.