Academic literature on the topic 'Microbe-mineral Interaction'

AbstractInterest in mineral–microbe interaction has grown enormously over recent decades, providing information in a puzzle-like manner which points towards an ever increasingly intimate relationship between the two; a relationship that can be truly termed co-evolution. Clay minerals play a very central role in this co-evolving system. Some 20 years ago, clay scientists looked at clay mineral–microbe studies as a peripheral interest only. Now, can clay scientists think that they understand the formation of clay minerals throughout geological history if they do not include life in their models? The answer is probably no, but we do not yet know the relative weight of biological and inorganic factors involved in driving clay-mineral formation and transformation. Similarly, microbiologists are missing out important information if they do not investigate the influence and modifications that minerals, particularly clay minerals, have on microbial activity and evolution. This review attempts to describe the several points relating clay minerals and microorganisms that have been discovered so far. The information obtained is still very incomplete and many opportunities exist for clay scientists to help to write the real history of the biosphere.

This article presents the progress on characterization of the interfacial interaction between sulfur oxidizing microbes and sulfide minerals by using of synchrotron radiation-based techniques including S/Fe/Cu X-ray absorption near-edge structure spectroscopy (XANES), X-ray Diffraction (XRD), micro-X-ray fluorescence (μ-XRF) mapping and micro-scanning transmission X-ray microscopy (μ-STXM) imaging, together with other accessory approaches such as SEM/EDS, Raman spectroscopy, FT-IR spectroscopy, and electrochemical methods as well as comparative proteomics methodology.

High microbial cell counts have been recorded in sewage waters employed as process water in mineral beneficiation plants across the world. The presence of these microbes can negatively impact flotation performance through mineral passivation, although some microbes improve flotation performance as investigated in various bio-flotation studies. The current study aims to understand the electrochemical behaviour of minerals in the presence of a sodium ethyl xanthate (SEX) collector and microbes originating from a sulphide ore processing plant in South Africa. The electrochemical response was correlated to observe flotation performance. Mixed potential measurements were conducted in parallel to microflotation tests, to assess the hydrophilicity or hydrophobicity induced on sulphide minerals adapted to microbe-laden synthetic plant water. Sulphide minerals’ mixed potentials and interactions of SEX with sulphide minerals were dramatically reduced in the presence of the mixed microbial community (MMC). The observations were correlated with poor flotation efficacy noted in microflotation tests. These fundamental results shed light on how the adsorption of thiol collectors on sulphide minerals is adversely affected by microbes, prompting a discussion on flotation process monitoring when mineral beneficiation is conducted using microbe-laden water.

In deep-sea hydrothermal environments, steep chemical and thermal gradients, rapid and turbulent mixing and biologic processes produce a multitude of diverse mineral phases and foster the growth of a variety of chemosynthetic micro-organisms. Many of these microbial species are associated with specific mineral phases, and the interaction of mineral and microbial processes are of only recently recognized importance in several areas of hydrothermal research. Many submarine hydrothermal mineral phases form during kinetically limited reactions and are either metastable or are only thermodynamically stable under in situ conditions. Laser Raman spectroscopy is well suited to mineral speciation measurements in the deep sea in many ways, and sea-going Raman systems have been built and used to make a variety of in situ measurements. However, the full potential of this technique for hydrothermal science has yet to be realized. In this focused review, we summarize both the need for in situ mineral speciation measurements in hydrothermal research and the development of sea-going Raman systems to date; we describe the rationale for further development of a small, low-cost sea-going Raman system optimized for mineral identification that incorporates a fluorescence-minimizing design; and we present three experimental applications that such a tool would enable.

AbstractSustaining Earth, in the face of both technology thrusts and population dynamics, depends on our ability to maintain a delicate balance between human-promoted planetary modification and decline thresholds for land (soils), water, atmosphere, and biological systems. Mineralogy, as much as any other single science, will be central to this process. A set of links between Earth sustainability issues and the science of mineralogy are formulated and discussed in this discourse. The strongest ties exist in the areas of mineral-water and mineral-atmosphere interactions. Minerals are also particularly important in human disease generation. In addition, due to the role of minerals as invaluable economic resources, the environmental consequences of mining also come into play. New subdisciplines have recently emerged to bring mineralogy even closer to Earth sustainability issues, particularly mineral-microbe interaction science and nanomineralogy

AbstractThe biogeochemical cycling of gold has been proposed from studies focusing on gold particle morphology, surface textures and associated bacteria living on the surface of gold particles. Additionally, it has been suggested that metabolically active bacteria on particles catalyse gold dissolution and gold re-precipitation processes, i.e. fluid–bacterial–mineral interaction within microenvironments surrounding particles. Therefore, the isolation and characterisation of viable bacteria from gold particles can be used as a model to improve the understanding of bacterial–gold interactions. In this study, classical microbiology methods were used to isolate a gold-tolerant bacterium (Acinetobacter sp. SK-43) directly from gold particles. The genome of this isolate contained diverse (laterally acquired) heavy-metal resistance genes and stress tolerance genes, suggesting that gene expression would confer resistance to a wide range of potentially toxic metals that could occur in the surrounding microenvironment. The presence of these genes, along with genes for nutrient cycling under nutrient-limited conditions highlights the genomic capacity of how Acinetobacter sp. SK-43 could survive on gold particles and remain viable. Laboratory experiments demonstrated that this isolate could grow in the presence of soluble gold up to 20 μM (AuCl3) and that >50% of soluble gold was reduced upon exposure. Collectively, these results suggest that Acinetobacter sp. SK-43 (and presumably similar bacteria) could survive the cytotoxic effects of soluble Au from particles undergoing dissolution. This study provides comprehensive insight on the possible bacterial contributions to gold biogeochemical cycling in natural environments.

A laboratory experiment was set up to demonstrate the capability of microbe to remediate petroleum hydrocarbon contaminated beach sand. Oil contaminated soil was used as a source of inoculum for hydrocarbon degrading bacteria (HDB) while oil contaminated beach sand was used as remediation object. The growth of HDB in the inocula was enriched and stimulated through the addition of nutrient in the form of vitamin and mineral as well the addition of oil waste as a source of carbon. Experiment took place in the course of approximately five weeks. Microscopic observation clearly showed the interaction between microbe and oil contaminant both in enrichment and bioremediation samples. The result of the experiment also suggests that approximately 25% of the petroleum hydrocarbon mass in the contaminated beach sand was biodegraded over the course of one month. Overall, the results of this experiment suggest the potential of bioremediation method to treat petroleum hydrocarbon polluted environment.Keywords: bacteria, bioremediation, hydrocarbon

Biological force microscopy (BFM) was developed to quantitatively measure pico- to nano-Newton forces (10-9 to 10-12 N) as a function of the nanoscale distance (nanometers) between living bacteria and mineral surfaces, in aqueous solution. Native cells were linked to a force-sensing probe, which was used in a force microscope to measure attractive and repulsive forces as a mineral surface approached, made contact with, and subsequently withdrew from a bacterium on the probe. The resulting data were used to interpret the interactive dynamics operative between bacteria and mineral surfaces under environmentally relevant conditions. BFM was used to study bacterial adhesion to mineral surfaces. In the case of Escherichia coli interactions with goethite, graphite, and muscovite, attractive and repulsive forces were detected at ranges up to 400 nanometers, the magnitude and sign depending on the ionic strength of the intervening solution and the mineral surface charge and hydrophobicity. Adhesion forces, up to several nanoNewtons in magnitude and exhibiting various fibrillation dynamics, were also measured and reflect the complex interactions of structural and chemical functionalities on the bacteria and mineral surfaces. In the study of Burkholderia cepecia interactions with mica, it was found that the physiological condition of the cell affected the observed adhesion forces. Cells grown under oligotrophic conditions exhibited an increased affinity for the mineral surface as opposed to cells grown under eutropic conditions. BFM was also used to characterize the transfer of electrons from biomolecules on Shewanella oneidensis to Fe(III) in the structure of goethite. Force measurements with picoNewton resolution were made in aqueous solution under aerobic and anaerobic conditions. Energy values (in attoJoules) derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions where electron transfer from bacterium to mineral is expected. Specific signatures in the force curves, analyzed with the worm-like chain model of protein unfolding, suggest that the bacterium recognizes the mineral surface such that a 150 kDa putative, iron reductase is quickly mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process.
Ph. D.

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.

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.

 

Les principaux objectifs étaient d'évaluer la stabilité de l'environnement des scories métallurgiques de Cu résultant de différentes périodes d'activités industrielles et de différentes technologies de fusion. Parmi les scories étudiées, on retrouve: les scories historiques cristallines (SH) ainsi que modernes: les scories de four vertical (SFS), les scories granulées (GS) et les scories de plomb (LS). Les différentes approches adoptées dans ce travail de thèse ont tenu compte de: i) la composition chimique et la phase minérale des scories, ii) la sensibilité à la lixiviation des scories sous l’exposition à différentes conditions de pH en mode statique, iii) l’altération des scories sous exposition aux acides organiques couramment trouvés dans l'environnement du sol, iv ) la bio-altération des scories par les bactéries (Pseudomonas aeruginosa) et v) l’application future de la récupération des métaux provenant des scories étudiées en mettant en œuvre la méthode de lixiviation biologique. Résultats cruciaux: Les résultats des tests de lixiviation dépendant du pH ont montré une libération de métal plus élevée dans des conditions fortement acides (pH 2 et 4), alors que la lixiviation dans des conditions alcalines (pH 10.5) était moins importante pour toutes les scories analysées. L'effet de l’altération par le sol a été démontré, la dissolution des scories est notamment sensible à la présence d'exsudats racinaires artificiels (ARE), d’acides humiques (HA) et d’acides fulviques (FA), la contribution des ARE étant la plus forte. Selon les données recueillies, la dissolution relative des scories est strictement liée à leurs caractéristiques (composition chimique et minéralogique) en fonction des différentes conditions étudiées. L'étude concernant l’effet de l’altération biologique a révélé que Pseudomonas aeruginosa améliore considérablement la libération des éléments majeurs (Si et Fe) et métalliques (Cu, Zn, Pb) par rapport aux effets des facteurs abiotiques, indépendamment de la chimie et de la structure des scories. En outre, une récupération élevée (jusqu'à 90%) des métaux (Cu, Zn, Fe) pourrait être obtenue grâce à la lixiviation avec Acidithiobacillus thiooxidans dans des conditions de laboratoire. Conclusions générales : La stabilité des scories dans l'environnement dépend à la fois des caractéristiques chimiques et de la minéralogie. Cependant, les phases minérales hébergeant les métaux sont les facteurs les plus déterminants concernant l'intensité de la lixiviation des métaux. Pour cette raison, l'examen individuel du comportement des scories est important pour empêcher la contamination de l'environnement et devrait être considéré comme une priorité pour la gestion durable des scories. L’optimisation des paramètres de fonctionnement pour le biolessivage et le développement de la technologie à l'échelle industrielle pourrait permettre une bien meilleure gestion (voir l’exploitation) des scories métallurgiques de Cu
Problem statement: Copper pyrometallurgical slags are inevitable waste by-products of Cu smelting operations. These waste are considered to be important due to their production volume and high residual metal content that are inefficiently recovered during industrial process. Due to the lack of sustainable practices in the past, tremendous volumes of Cu-slags have been disposed in many industrial districts, regardless of the weathering and associated environmental risk. Consequently, there are many areas where slags have been proven to be a source of metallic pollution for the surrounding environment. At the present time, the outstanding contradiction between the sustainable development and environmental pollution encourages to undertake the action regarding this aspect. For this reason, slags are currently being used as supplementary materials for civil engineering purposes (e.g. cement and concrete additives, road bed filling materials, hydraulic construction materials) rather than disposed. Additionally, modern-day management strategies require slags to be thoroughly evaluated with respect to their environmental stability prior undertaking any reuse action. Main objectives were to evaluate environmental stability of Cu-metallurgical slags resulting from different periods of industrial activities and different smelting technologies. Those included: historical crystalline slag (HS) as well as modern: shaft furnace slag (SFS), granulated slag (GS) and lead slag (LS). Different approaches undertaken in this PhD work considered: i) chemical and mineral phase compositions of slags, ii) leaching susceptibility of slags under exposure to different pH-stat conditions, iii) slags weathering under exposure to organic acids commonly found in soil environment, iv) bacterially (Pseudomonas aeruginosa) mediated weathering of slags and v) future application of studied slags for metal recovery by implementing the bioleaching method. Crucial results: The results of the pH-dependent leaching tests showed a higher metal release in strong acidic conditions (pH 2 and 4), whereas leachability at alkaline conditions (pH 10.5) revealed a lower importance for all the slags analyzed. The study considering soil weathering scenario demonstrated that Cu-slags are susceptible to dissolution in the presence of artificial root exudates (ARE), humic (HA) and fulvic acids (FA), whereby ARE were found to have stronger contribution than HA and FA. According to data collected, the different behavior of individual slags is strictly related to their characteristics (chemical and phase composition) reflecting various susceptibilities to dissolution under the investigated conditions. The study considering bio-weathering scenario revealed that Pseudomonas aeruginosa considerably enhances the release of major (Si and Fe) and metallic (Cu, Zn, Pb) elements compared to the effects of abiotic factors, regardless of the slags chemistry and structure. Furthermore, a high gain (up to 90%) of metals (Cu, Zn, Fe) could be credited to bioleaching with Acidithiobacillus thiooxidans under laboratory conditions. General conclusions: The environmental stability of slags depends on both, their bulk chemistry and mineralogy. However, mineral phases harbouring the metals are the key players in metal leachability intensity. For, this reason consideration of individual slags behaviour is important for preventing environmental contamination and should be regarded as priority branch of sustainable slag management. Optimization of operating parameters for bioleaching following development of industrial scale technology is an incentive scheme for future management of Cu-metallurgical slags

The most significant environmental issue that has arisen in the mining industries over the last decade is that of acid mine drainage (AMD) from tailing dumps and waste mined rock piles. AMD is caused by the oxidation of sulphide minerals followed by leaching and flushing of the product into the receiving environment. Pyrite, chalcopyrite, quartz, and calcite are the most common sulfide and oxide gangue minerals present in tailing dumps originating from the mining operations all over the world. The mining operations results in the exposure of sulfide bearing minerals which has the capacity to produce acid mine drainage (AMD) for which control measures are necessary to protect the environment. Sulfide minerals such as pyrite (FeS2) are oxidized to sulfate when water, containing oxygen, infiltrates the tailings. Paenibacillus polymyxa is a Gram-positive, neutrophilic, peri flagellated heterotroph indigenously associated with many mineral deposits. Extracellular polysaccharides, proteins, and organic acids such as oxalic acid, formic acid and acetic acid are the principal components of the biomass obtained from Paenibacillus polymyxa. The current investigation was initiated to develop a bioremediation process to counter AMD problem and interrogate microbially-induced flotation and flocculation behavior of various sulphide and oxide minerals when present alone or in different combinations. The system initially considered consists of oxides such as quartz and calcite and sulphides such as pyrite and chalcopyrite. The prime objective with this system was to develop a process with Paenibacillus polymyxa cells and metabolic products, which would lead to a separation of unwanted pyrite and chalcopyrite from the oxides. After successful attempt with bacterial cells and metabolite, investigations were extended with major extracellular bacterial bioreagents present in metabolite such as proteins and polysaccharides. These bioreagents were observed to show different adsorption density onto different minerals. Selective separation with these extracellular bioreagents was also achieved. Studies were later extended to include the sulphide minerals such as sphalerite and galena and mixtures of quartz, calcite, pyrite, chalcopyrite, sphalerite, and galena. Besides the success of selective separation of desired minerals from different synthetic minerals system, detailed investigations were also carried out to examine the surface chemical behavior of various minerals in course of microbe-minerals interactions. Cell wall and their associated bioentites were isolated to examine their contribution towards microbe-mineral interactions. Major objectives of this investigation are outlined as below. 1. The basic principles and mechanisms governing microbe-mineral interactions were examined from the viewpoint of desulphurization of AMD tailings and microbially-induced mineral flotation and flocculation. Detailed elucidation of surface chemical changes brought about by the microbe-mineral interactions is discussed with respect to surface chemical and bio dissolution studies. Besides bacterial cells the role of bacterial metabolite and associated extracellular proteins and polysaccharides in bringing about bacterial adhesion, modulation of surface properties of the minerals with respect to hydrophilicity and hydrophobicity and dissolution, along with development of probable mechanisms of microbe-mineral interactions are discussed. 2. Minerals were characterized to ascertain their purity through X-Ray diffraction and mineralogical analysis. SEM micrographic analysis was also carried out for the characterization of bacterial cells. Pure culture of bacteria was acquired through pour plating procedure. The investigation was commenced by characterizing both minerals and bacterium in the following ways • Mineral samples were ground and sieved to obtain different size fractions. The size fractions were separated in two major groups, i.e. finer sizes, and coarser sizes. Finer particles were further ground to obtain very fine colloidal particles (< 5 microns). These fines were used for adsorption, electrokinetic, flocculation and bio dissolution studies. Coarser particles were used for flotation studies. Surface area of the minerals was also determined. • To ascertain the purity of the bacterium it was pour plated and a pure colony was isolated and further recultured for different studies. The cell count was studied, and a growth curve was established. Besides, pH of the bacterial culture was also examined at regular intervals as it was an imported parameter in major part of this investigation. Bacterial culture was grown in presence of different minerals in order to observe any possible changes in their effect onto different minerals and separation processes. 3. It is generally believed that the effect of bacterial cells onto a mineral substrate is directly dependent on the cell count associated per unit mineral surface area. Hence the investigation was initiated by studying the measurement of adsorption density onto minerals as a function of time. The results obtained from these studies prompted to examine the adsorption behavior with respect to pH and also establishment of adsorption isotherms to understand the pattern they form in course of adsorption process. As an attempt to understand the interfacial reagents associated in adsorption process, studies were carried out with bacterial metabolite, extracellular product, and cell wall bioreagents. Adsorption of bioreagents were also compared with chemical reagents used in mineral processing. To determine the comparative affinity of proteins and polysaccharides onto individual minerals, adsorption studies were also carried out in different sequences. SEM micrographic analysis was also successful to ascertain the specificity of the bacterial cells towards different minerals observed in the earlier studies. 4. The zeta potential values of bacterial cells and minerals considered in this investigation were determined. The effect of pH, interaction time and reagent concentration on the zeta potential values of minerals and bacterial cells after mutual interaction with each other, has been evaluated. Zeta potential of minerals after interaction with extracellular bioreagents as well as cell wall associated bio entities was also measured. 5. Settling behavior of individual minerals after interaction with bacterial cells as well all associated bioentites has been studied. These studies revealed different possibilities of selective separation of individual minerals from different synthetic mineral systems. 6. Micro flotation studies have been conducted on single mineral systems in order to assess the changes in their hydrophobicity and hydrophilicity, consequent to interaction with the bacterial cells, the metabolic products and also the cell wall associated bioreagents. These studied showed different possibilities of selective separation of individual minerals from different systems. Additional surfactant was also used in these experiments to enhance the efficiency of separation processes. 7. Bio dissolution studies were also carried out with bacterial culture, metabolite, and metabolic products. 8. Bioreagents were isolated from the minerals surface subsequent to adsorption process. Presence of different bioreagents was assured through various self-developed techniques. It was interesting to note that specific group of proteins are involved in driving the adsorption processes for individual minerals. Hence investigation was extended to purify the proteins and their effect on the minerals was studied. 9. Extracellular bacterial protein after characterizing through SDS PAGE technique revealed that it consists of numerous groups of different proteins. Initially EBP was fractionated through ammonium sulphate precipitation procedure. Further purification of the proteins was attempted with different chromatographic techniques such as Ion exchange chromatography and FPLC chromatographic techniques. Purified protein fractions obtained from these experiments were used for adsorption studies. The results obtained from these experiments strengthen the fact that there are specific proteins available in EBP, which show selective affinity towards different minerals. 10. Since bacterial cells were washed thoroughly prior to their studies with minerals it was assumed that the cell wall bio entities may play a prime role. Hence proteins and polysaccharide associated with the cell wall was separated and their effect onto the minerals was studied. Partial characterization of proteins was attempted through SDS PAGE technique. 11. In order to gain better understanding of the mechanisms of microbe-mineral interactions, ruthenium red adsorption, protein assay and cell surface hydrophobicity tests have been conducted. Cursory experiments have been performed to characterize the secreted proteins and polysaccharides using SDS PAGE electrophoresis techniques, mass spectrometry and NMR techniques. Major conclusions based on this work are summarized below. Bacterial cells showed higher affinity towards pyrite, chalcopyrite and galena compared to sphalerite, calcite, and quartz. The adsorption isotherms studies showed that the adsorption patterns of bacterial cells onto the minerals were different. Pyrite and chalcopyrite showed highest adsorption of EBP whereas ECP adsorption was higher onto galena, pyrite, and chalcopyrite. S-Layer protein adsorption was higher on pyrite and chalcopyrite. Plasma membrane protein was higher onto quartz and was quite reasonable onto chalcopyrite. Adsorption of Cell Wall polysaccharides was observed to be the highest onto galena. Adsorption of all the above bioreagents along with PIPX showed that pyrite and chalcopyrite hardly accommodated any PIPX onto its surface. Similar phenomenon was observed with adsorption of ECP onto galena. Electrokinetic studies showed shift in IEP values for quartz, calcite, and sphalerite. Since galena, pyrite and chalcopyrite gets flocculated with bacterial cells or associated bioreagents there was no shift in IEP observed in these cases. Galena, pyrite, and chalcopyrite was observed to get flocculated with cells and the effect was prominent with pyrite and chalcopyrite. Quartz was observed to show dispersion characteristics with cells and EBP. Other bioreagents were observed to show differences in the settling properties with individual minerals. This led to selective separation of pyrite and chalcopyrite from their mixture with other minerals. Micro flotation of individual minerals also showed difference in floatability with bacterial cells and all the other bioreagents also. Pyrite and chalcopyrite were depressed with bacterial cells and hence were used to selectively separate from other minerals. Similar behavior was also observed with other bioreagents. Use of collector was observed to improve the efficiency in many cases. Characterization showed that EBP consisted of numerous proteins. Hence purification of protein was attempted to isolate individual or groups of proteins through Ammonium sulphate precipitation techniques, ION exchange and FPLC chromatography techniques. It was observed that proteins involved in adsorption, flocculation and flotation were mineral-specific proteins. Hydrophobicity studies revealed that bacterial cells develop both hydrophobic and hydrophilic characteristics when interacted with different minerals. Finally, ruthenium red adsorption onto mineral-adapted bacterial cells revealed that galena adapted cells produced the highest number of polysaccharides. Similarly, protein assay test showed that pyrite/chalcopyrite-adapted cells lead to higher amount of secreted proteins. Characterization of ECP showed that it consisted of a wide range of carbohydrate related functional groups.

A gradual depletion of high-grade ores, coupled with the growing demand for mineral commodities across the world has culminated in the increased exploitation of lean-grade ores with complex mineralogy. The mineral processing industry commonly uses an extensive range of inorganic, naturally derived or synthetic organic reagents in the separation of valuable minerals from the ore. Froth flotation is a commonly used separation technique to float or depress different sulfide minerals from the ore, based on their surface properties. In recent times, biological processes have been attracting attention in mineral processing and metal recovery operations due to a number of factors, especially lower operating costs, lesser energy consumption and their environment friendly nature. The use of microorganisms and their direct derivatives in mineral processing, hydrometallurgy and in the bioremediation of mineral industry discharges has led to the emerging area of “Mineral Bioprocessing”. In this study, a family of four microorganisms belonging to the Bacillus species, viz., Paenibacillus polymyxa, Bacillus circulans, Bacillus megaterium and Bacillus subtilis was used to ascertain the selective floatability of sphalerite from a sphalerite-galena mineral mixture. These bacteria are Gram positive, mesophilic, neutrophilic, aerobic and spore forming. The major objectives of the investigation include: a) Identification and characterization of bioreagents derived from Bacillus species for the flotation of sphalerite from a sphalerite-galena mixture b) Optimization of the flotation process for the enhanced recovery of sphalerite using specific bioreagent combinations c) Modes and mechanisms of bacterial adaptation to minerals and their consequent effects on the flotation of sphalerite and galena d) Elucidation of the mechanisms of microbe-mineral interactions and the role of extracellular secretions in sphalerite flotation column and their N-terminal residues were identified using Edmann N-terminal sequencing. Additionally, sequences of several internal peptides from both the proteins were determined using Tandem Mass Spectrometric techniques. A database search revealed that the sequences of these peptides are unique and have not been reported earlier. It was established that the bacterial cells give high flotation recovery of sphalerite under buffered conditions and that it took place only in the presence of anionic buffers. Additionally, the viability of the bacterial cells was not required for the flotation of minerals. A major finding of this study was that other than extracellular DNA (eDNA), none of the other bacterial surface components like teichoic acids, surface proteins, polysaccharides played a positive role in the flotation process. Nucleic acids, more particularly single stranded DNA (ssDNA), facilitated sphalerite flotation relative to double stranded DNA (dsDNA). A probable mechanism of ssDNA -mediated selective flotation of sphalerite has been presented. A negative role for non-DNA surface components was also observed. This led to the realization of the need for an optimum ratio of DNA to non-DNA components in the selective flotation of sphalerite from a sphalerite-galena mixture. It was found that the surface physiochemical properties of the mineral adapted bacteria differed significantly from that of the unadapted bacteria. Adaptation enhanced the flotation recoveries of the corresponding mineral vis-à-vis the unadapted bacteria. Sphalerite adapted bacteria secreted more extracellular proteins while the galena adapted bacteria secreted more polysaccharides compared to the unadapted bacteria. Sphalerite adapted bacteria selectively floats more sphalerite from the mineral mixture than the galena adapted as well as the unadapted bacteria. It was evident from the electrokinetic studies that the surface charge of the chosen sulfide mineral adapted bacteria was less negative relative to the unadapted bacteria. This phenomenon was observed with all the four bacterial species used in this study. A noteworthy finding was that the bacteria especially B.circulans induce a change in morphology from rod to sphere as a strategy during adaptation to a toxic mineral such as galena. This phenomenon has been shown to involve changes in crucial cell wall components as well as changes in the levels of expression of bacterial cytoskeleton elements involved in the maintenance of the rod shape. This aspect of the study involved the partial sequencing of the B.circulans homolog of the key cytoskeleton gene, mreB (B gene in murien cluster e), using the Polymerase Chain Reaction (PCR) followed by DNA sequencing. A Genbank search indicated that this is the first report of the sequence of B.circulans mreB gene. This was followed by measuring the hypothesized downward changes in the levels of expression of the mreB gene by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The possible mechanisms of the adaptive morphological changes and of the interaction of the chosen sulfide minerals with the family of microorganisms studied have been discussed with respect to their bioflotation efficiency.

A gradual depletion of high-grade ores, coupled with the growing demand for mineral commodities across the world has culminated in the increased exploitation of lean-grade ores with complex mineralogy. The mineral processing industry commonly uses an extensive range of inorganic, naturally derived or synthetic organic reagents in the separation of valuable minerals from the ore. Froth flotation is a commonly used separation technique to float or depress different sulfide minerals from the ore, based on their surface properties. In recent times, biological processes have been attracting attention in mineral processing and metal recovery operations due to a number of factors, especially lower operating costs, lesser energy consumption and their environment friendly nature. The use of microorganisms and their direct derivatives in mineral processing, hydrometallurgy and in the bioremediation of mineral industry discharges has led to the emerging area of “Mineral Bioprocessing”. In this study, a family of four microorganisms belonging to the Bacillus species, viz., Paenibacillus polymyxa, Bacillus circulans, Bacillus megaterium and Bacillus subtilis was used to ascertain the selective floatability of sphalerite from a sphalerite-galena mineral mixture. These bacteria are Gram positive, mesophilic, neutrophilic, aerobic and spore forming. The major objectives of the investigation include: a) Identification and characterization of bioreagents derived from Bacillus species for the flotation of sphalerite from a sphalerite-galena mixture b) Optimization of the flotation process for the enhanced recovery of sphalerite using specific bioreagent combinations c) Modes and mechanisms of bacterial adaptation to minerals and their consequent effects on the flotation of sphalerite and galena d) Elucidation of the mechanisms of microbe-mineral interactions and the role of extracellular secretions in sphalerite flotation column and their N-terminal residues were identified using Edmann N-terminal sequencing. Additionally, sequences of several internal peptides from both the proteins were determined using Tandem Mass Spectrometric techniques. A database search revealed that the sequences of these peptides are unique and have not been reported earlier. It was established that the bacterial cells give high flotation recovery of sphalerite under buffered conditions and that it took place only in the presence of anionic buffers. Additionally, the viability of the bacterial cells was not required for the flotation of minerals. A major finding of this study was that other than extracellular DNA (eDNA), none of the other bacterial surface components like teichoic acids, surface proteins, polysaccharides played a positive role in the flotation process. Nucleic acids, more particularly single stranded DNA (ssDNA), facilitated sphalerite flotation relative to double stranded DNA (dsDNA). A probable mechanism of ssDNA -mediated selective flotation of sphalerite has been presented. A negative role for non-DNA surface components was also observed. This led to the realization of the need for an optimum ratio of DNA to non-DNA components in the selective flotation of sphalerite from a sphalerite-galena mixture. It was found that the surface physiochemical properties of the mineral adapted bacteria differed significantly from that of the unadapted bacteria. Adaptation enhanced the flotation recoveries of the corresponding mineral vis-à-vis the unadapted bacteria. Sphalerite adapted bacteria secreted more extracellular proteins while the galena adapted bacteria secreted more polysaccharides compared to the unadapted bacteria. Sphalerite adapted bacteria selectively floats more sphalerite from the mineral mixture than the galena adapted as well as the unadapted bacteria. It was evident from the electrokinetic studies that the surface charge of the chosen sulfide mineral adapted bacteria was less negative relative to the unadapted bacteria. This phenomenon was observed with all the four bacterial species used in this study. A noteworthy finding was that the bacteria especially B.circulans induce a change in morphology from rod to sphere as a strategy during adaptation to a toxic mineral such as galena. This phenomenon has been shown to involve changes in crucial cell wall components as well as changes in the levels of expression of bacterial cytoskeleton elements involved in the maintenance of the rod shape. This aspect of the study involved the partial sequencing of the B.circulans homolog of the key cytoskeleton gene, mreB (B gene in murien cluster e), using the Polymerase Chain Reaction (PCR) followed by DNA sequencing. A Genbank search indicated that this is the first report of the sequence of B.circulans mreB gene. This was followed by measuring the hypothesized downward changes in the levels of expression of the mreB gene by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The possible mechanisms of the adaptive morphological changes and of the interaction of the chosen sulfide minerals with the family of microorganisms studied have been discussed with respect to their bioflotation efficiency.

‘Minerals and the living world’ considers various mineral–microbe interactions, biomineralization, and how minerals interact with the human body and human health. Biomineralization is the process where living organisms produce minerals such as calcite, apatite, and silica. An example is the unicellular, ocean-living radiolaria that have complex silica skeletons. After death their skeletal remains sink to the ocean floor and can be seen preserved in cherts and flints. Human biominerals can be divided into those which are an essential part of the bodies’ systems, such as hydroxylapatite found in bones and teeth, and those which are unexpected and pathological mineral deposits, such as calcium oxalate and asbestiform minerals.

Nitrogen fertilizers are one of the highest expenses in agricultural systems and usually a limitation to the productions of many agricultural crops worldwide. The intensive use of this element in modern agriculture represents a potential environmental threat, one of the many tools for the sustainable use of this resource without losing productivity is the use of plant growth-promoting rhizobacteria, especially nitrogen-fixing bacteria. However, in considering the competitiveness of the market, studies are still needed to determine the most efficient way to use this resource and if the nitrogen mineral fertilization is indeed substitutable. As a result, this study aims to deepen the scientific knowledge of the plant-microbe interactions by addressing their main characteristics and functionalities for plant growth and development and efficiency in the use of nitrogen. For this we reviewed relevant information from scientific works that address these issues.