Metallosphaera javensis sp. nov., a novel species of thermoacidophilic archaea, isolated from a volcanic area.

A novel thermoacidophilic archeaon, strain J1T (=DSM 112778T,=JCM 34702T), was isolated from a hot pool in a volcanic area of Java, Indonesia. Cells of the strain were irregular, motile cocci of 1.0-1.2 µm diameter. Aerobic, organoheterotrophic growth with casamino acids was observed at an optimum temperature of 70 °C in a range of 55-78 °C and at an optimum pH of 3 in a range of 1.5 to 5. Various organic compounds were utilized, including a greater variety of sugars than has been reported for growth of other species of the genus. Chemolithoautotrophic growth was observed with reduced sulphur compounds, including mineral sulphides. Ferric iron was reduced during anaerobic growth with elemental sulphur. Cellular lipids were calditoglycerocaldarchaeol and caldarchaeol with some derivates. The organism contained the respiratory quinone caldariellaquinone. On the basis of phylogenetic and chemotaxonomic comparison with its closest relatives, it was concluded that strain J1T represents a novel species, for which the name Metallosphaera javensis is proposed. Low DNA-DNA relatedness values (16S rRNA gene <98.4%, average nucleotide identity (ANI) <80.1%) distinguished J1T from other species of the genus Metallosphaera and the DNA G+C content of 47.3% is the highest among the known species of the genus.

Progress in bioleaching: part B, applications of microbial processes by the minerals industries.

This review provides an update to the last mini-review with the same title pertaining to recent developments in bioleaching and biooxidation published in 2013 (Brierley and Brierley). In the intervening almost 10 years, microbial processes for sulfide minerals have seen increased acceptance and ongoing but also declining commercial application in copper, gold, nickel and cobalt production. These processes have been applied to heap and tank leaching, nowadays termed biomining, but increasing concerns about the social acceptance of mining has also seen the re-emergence of in situ leaching and quest for broader applicability beyond uranium and copper. Besides metal sulfide oxidation, mineral dissolution via reductive microbial activities has seen experimental application to laterite minerals. And as resources decline or costs for their exploitation rise, mine waste rock and tailings have become more attractive to consider as easily accessible resources. As an advantage, they have already been removed from the ground and in some cases contain ore grades exceeding that of those currently being mined. These factors promote concepts of circular economy and efficient use and valorization of waste materials. KEY POINTS: • Bioleaching of copper sulfide ore deposits is producing less copper today • Biooxidation of refractory gold ores is producing more gold than in the past • Available data suggest bioleaching and biooxidation processes reduce carbon emissions.

Progress in bioleaching: fundamentals and mechanisms of microbial metal sulfide oxidation - part A.

Bioleaching of metal sulfides is performed by diverse microorganisms. The dissolution of metal sulfides occurs via two chemical pathways, either the thiosulfate or the polysulfide pathway. These are determined by the metal sulfides' mineralogy and their acid solubility. The microbial cell enables metal sulfide dissolution via oxidation of iron(II) ions and inorganic sulfur compounds. Thereby, the metal sulfide attacking agents iron(III) ions and protons are generated. Cells are active either in a planktonic state or attached to the mineral surface, forming biofilms. This review, as an update of the previous one (Vera et al., 2013a), summarizes some recent discoveries relevant to bioleaching microorganisms, contributing to a better understanding of their lifestyle. These comprise phylogeny, chemical pathways, surface science, biochemistry of iron and sulfur metabolism, anaerobic metabolism, cell-cell communication, molecular biology, and biofilm lifestyle. Recent advances from genetic engineering applied to bioleaching microorganisms will allow in the future to better understand important aspects of their physiology, as well as to open new possibilities for synthetic biology applications of leaching microbial consortia. KEY POINTS: • Leaching of metal sulfides is strongly enhanced by microorganisms • Biofilm formation and extracellular polymer production influences bioleaching • Cell interactions in mixed bioleaching cultures are key for process optimization.

Distribution of Acidophilic Microorganisms in Natural and Man-made Acidic Environments.

Acidophilic microorganisms can thrive in both natural and man-made environments. Natural acidic environments comprise hydrothermal sites on land or in the deep sea, cave systems, acid sulfate soils and acidic fens, as well as naturally exposed ore deposits (gossans). Man-made acidic environments are mostly mine sites including mine waste dumps and tailings, acid mine drainage and biomining operations. The biogeochemical cycles of sulfur and iron, rather than those of carbon and nitrogen, assume centre stage in these environments. Ferrous iron and reduced sulfur compounds originating from geothermal activity or mineral weathering provide energy sources for acidophilic, chemolithotrophic iron- and sulfur-oxidizing bacteria and archaea (including species that are autotrophic, heterotrophic or mixotrophic) and, in contrast to most other types of environments, these are often numerically dominant in acidic sites. Anaerobic growth of acidophiles can occur via the reduction of ferric iron, elemental sulfur or sulfate. While the activities of acidophiles can be harmful to the environment, as in the case of acid mine drainage, they can also be used for the extraction and recovery of metals, as in the case of biomining. Considering the important roles of acidophiles in biogeochemical cycles, pollution and biotechnology, there is a strong need to understanding of their physiology, biochemistry and ecology.

Sulfobacillus harzensis sp. nov., an acidophilic bacterium inhabiting mine tailings from a polymetallic mine.

A mixotrophic and acidophilic bacterial strain BGR 140T was isolated from mine tailings in the Harz Mountains near Goslar, Germany. Cells of BGR 140T were Gram-stain-positive, endospore-forming, motile and rod-shaped. BGR 140T grew aerobically at 25-55 °C (optimum 45 °C) and at pH 1.5-5.0 (optimum pH 3.0). The results of analysis of the 16S rRNA gene sequences indicated that BGR 140T was phylogenetically related to different members of the genus Sulfobacillus, and the sequence identities to Sulfobacillus acidophilus DSM 10332T, Sulfobacillus thermotolerans DSM 17362T, and Sulfobacillus benefaciens DSM 19468T were 94.8, 91.8 and 91.6 %, respectively. Its cell wall peptidoglycan is A1γ, composed of meso-diaminopimelic acid. The respiratory quinone is DMK-6. The major polar lipids were determined to be glycolipid, phospholipid and phosphatidylglycerol. The predominant fatty acid is 11-cycloheptanoyl-undecanoate. The genomic DNA G+C content is 58.2 mol%. On the basis of the results of phenotypic and genomic analyses, it is concluded that strain BGR 140T represents a novel species of the genus Sulfobacillus, for which the name Sulfobacillus harzensis sp. nov. is proposed because of its origin. Its type strain is BGR 140T (=DSM 109850T=JCM 39070T).

Uranium Isotope Fractionation during the Anoxic Mobilization of Noncrystalline U(IV) by Ligand Complexation.

Uranium (U) isotopes are suggested as a tool to trace U reduction. However, noncrystalline U(IV), formed predominantly in near-surface environments, may be complexed and remobilized using ligands under anoxic conditions. This may cause additional U isotope fractionation and alter the signatures generated by U reduction. Here, we investigate the efficacy of noncrystalline U(IV) mobilization by ligand complexation and the associated U isotope fractionation. Noncrystalline U(IV) was produced via the reduction of U(VI) (400 µM) by Shewanella oneidensis MR-1 and was subsequently mobilized with EDTA (1 mM), citrate (1 mM), or bicarbonate (500 mM) in batch experiments. Complexation with all investigated ligands resulted in significant mobilization of U(IV) and led to an enrichment of 238U in the mobilized fraction (δ238U = 0.4-0.7 ‰ for EDTA; 0.3 ‰ for citrate; 0.2-0.3 ‰ for bicarbonate). For mobilization with bicarbonate, a Rayleigh approach was the most suitable isotope fractionation model, yielding a fractionation factor α of 1.00026-1.00036. Mobilization with EDTA could be modeled with equilibrium isotope fractionation (α: 1.00039-1.00049). The results show that U isotope fractionation associated with U(IV) mobilization under anoxic conditions is significant and needs to be considered when applying U isotopes in remediation monitoring or as a paleo-redox proxy.

Manganese-Cycling Microbial Communities Inside Deep-Sea Manganese Nodules.

Polymetallic nodules (manganese nodules) have been formed on deep sea sediments over millions of years and are currently explored for their economic potential, particularly for cobalt, nickel, copper, and manganese. Here we explored microbial communities inside nodules from the northeastern equatorial Pacific. The nodules have a large connected pore space with a huge inner surface of 120 m(2)/g as analyzed by computer tomography and BET measurements. X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis revealed a complex chemical fine structure. This consisted of layers with highly variable Mn/Fe ratios (<1 to >500) and mainly of turbostratic phyllomanganates such as 7 and 10 Švernadites alternating with layers of Fe-bearing vernadite (δ-MnO2) epitaxially intergrown with amorphous feroxyhyte (δ-FeOOH). Using molecular 16S rRNA gene techniques (clone libraries, pyrosequencing, and real-time PCR), we show that polymetallic nodules provide a suitable habitat for prokaryotes with an abundant and diverse prokaryotic community dominated by nodule-specific Mn(IV)-reducing and Mn(II)-oxidizing bacteria. These bacteria were not detected in the nodule-surrounding sediment. The high abundance and dominance of Mn-cycling bacteria in the manganese nodules argue for a biologically driven closed manganese cycle inside the nodules relevant for their formation and potential degradation.

Microbial community stratification controlled by the subseafloor fluid flow and geothermal gradient at the Iheya North hydrothermal field in the Mid-Okinawa Trough (Integrated Ocean Drilling Program Expedition 331).

The impacts of lithologic structure and geothermal gradient on subseafloor microbial communities were investigated at a marginal site of the Iheya North hydrothermal field in the Mid-Okinawa Trough. Subsurface marine sediments composed of hemipelagic muds and volcaniclastic deposits were recovered through a depth of 151 m below the seafloor at site C0017 during Integrated Ocean Drilling Program Expedition 331. Microbial communities inferred from 16S rRNA gene clone sequencing in low-temperature hemipelagic sediments were mainly composed of members of the Chloroflexi and deep-sea archaeal group. In contrast, 16S rRNA gene sequences of marine group I Thaumarchaeota dominated the microbial phylotype communities in the coarse-grained pumiceous gravels interbedded between the hemipelagic sediments. Based on the physical properties of sediments such as temperature and permeability, the porewater chemistry, and the microbial phylotype compositions, the shift in the physical properties of the sediments is suggested to induce a potential subseafloor recharging flow of oxygenated seawater in the permeable zone, leading to the generation of variable chemical environments and microbial communities in the subseafloor habitats. In addition, the deepest section of sediments under high-temperature conditions (∼90°C) harbored the sequences of an uncultivated archaeal lineage of hot water crenarchaeotic group IV that may be associated with the high-temperature hydrothermal fluid flow. These results indicate that the subseafloor microbial community compositions and functions at the marginal site of the hydrothermal field are highly affected by the complex fluid flow structure, such as recharging seawater and underlying hydrothermal fluids, coupled with the lithologic transition of sediments.

Rates of iron(III) reduction coupled to elemental sulfur or tetrathionate oxidation by acidophilic microorganisms and detection of sulfur intermediates.

Bioleaching processes and acid mine drainage (AMD) generation are mainly driven by aerobic microbial iron(II) and inorganic sulfur/compound oxidation. Dissimilatory iron(III) reduction coupled to sulfur/compound oxidation (DIRSO) by acidophilic microorganisms has been described for anaerobic cultures, but iron reduction was observed under aerobic conditions as well. Aim of this study was to explore reaction rates and mechanisms of this process. Cell-specific iron(III) reduction rates for different Acidithiobacillus (At.) strains during batch culture growth or stationary phase with iron(III) (∼40 mM) as electron acceptor and elemental sulfur or tetrathionate as electron donor (1% or 5 mM, respectively) were determined. The rates were highest under anaerobic conditions for the At. ferrooxidans type strain with 6.8 × 106 and 1.1 × 107 reduced iron(III) ions per second per cell for growth on elemental sulfur and tetrathionate, respectively. The iron(III) reduction rates were somehow lower for the anaerobically sulfur grown archaeon Ferroplasma acidiphilum, and lowest for the sulfur grown At. caldus type strain under aerobic conditions (1.7 × 106 and 7.3 × 104 reduced iron(III) ions per second per cell, respectively). The rates for five strains of At. thiooxidans (aerobe) were in between those for At. ferrooxidans (anaerobe) and At. caldus (aerobe). There was no pronounced pH dependence of iron(III) reduction rates in the range of pH 1.0-1.9 for the type strains of all species but rates increased with increasing pH for four other At. thiooxidans strains. Thiosulfate as sulfur intermediate was found for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III) but not during anaerobic growths on elemental sulfur and iron(III), and a small concentration was measured during aerobic growths on tetrathionate without iron(III). For the At. thiooxidans type strain thiosulfate was found with tetrathionate grown cells under aerobic conditions in presence and absence of iron(III), but not with sulfur grown cells. Evidence for hydrogen sulfide production at low pH was found for the At. ferrooxidans as well as the At. thiooxidans type strains during microaerophilic growth on elemental sulfur and for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III). The occurrence of sulfur compound intermediates supports the hypothesis that chemical reduction of iron(III) ions takes place by sulfur compounds released by the microbial cells.

Goethite dissolution by acidophilic bacteria.

Previous studies have reported the role of some species of acidophilic bacteria in accelerating the dissolution of goethite under aerobic and anaerobic conditions. This has relevance for environments impacted by acid mine drainage and for the potential bioleaching of limonitic laterite ores. In this study, natural well-characterized goethite mineral samples and synthetic goethite were used in aerobic and anaerobic laboratory batch culture incubation experiments with ferric iron-reducing, acidophilic bacteria, including the lithoautotrophic species Acidithiobacillus (At.) thiooxidans, At. ferrooxidans, and At. caldus, as well as two strains of the organoheterotrophic species Acidiphilium cryptum. All bacteria remained alive throughout the experiments and efficiently reduced soluble ferric iron in solution in positive control assays. However, goethite dissolution was low to negligible in all experimental assays with natural goethite, while some dissolution occurred with synthetic goethite in agreement with previous publications. The results indicate that ferric iron-reducing microbial activity at low pH is less relevant for goethite dissolution than the oxidation of elemental sulfur to sulfuric acid. Microbial ferric iron reduction enhances but does not initiate goethite dissolution in very acidic liquors.

Do ferrous iron-oxidizing acidophiles (Leptospirillum spp.) disturb aerobic bioleaching of laterite ores by sulfur-oxidizing acidophiles (Acidithiobacillus spp.)?

The extraction of nickel, cobalt, and other metals from laterite ores via bioleaching with sulfur-oxidizing and ferric iron-reducing, autotrophic, acidophilic bacteria (e.g. Acidithiobacillus species) has been demonstrated under anaerobic as well as aerobic conditions in experiments in different laboratories. This study demonstrated the bioleaching of laterites from Brazil with the addition of elemental sulfur in 2-L stirred-tank bioreactors with pure and mixed cultures of Acidithiobacillus and Sulfobacillus species under aerobic conditions. In particular, a potential disturbance of mineral dissolution under aerobic conditions by ferrous iron-oxidizing acidophiles likely introduced as contaminants in an applied bioleaching process was investigated with Leptospirillum ferrooxidans at 30°C and Leptospirillum ferriphilum at 40°C, at maintained pH 1.5 or without maintained pH leading to an increase in acidity (with pH values <1.0) due to the biological production of sulfuric acid. Despite the proportion of ferrous iron to the total amount of extracted iron in the solution being drastically reduced in the presence of Leptospirillum species, there was a negligible effect on the extraction efficiency of nickel and cobalt, which is positive news for laterite bioleaching under aerobic conditions.

Comparison of bioleaching of a sulfidic copper ore (chalcopyrite) in column percolators and in stirred-tank bioreactors including microbial community analysis.

Chalcopyrite is the most abundant Cu-sulfide and economically the most important copper mineral in the world. It is known to be recalcitrant in hydrometallurgical processing and therefore chalcopyrite bioleaching has been thoroughly studied for improvement of processing. In this study, the microbial diversity in 22 samples from the Sarcheshmeh copper mine in Iran was investigated via 16S rRNA gene sequencing. In total, 1063 species were recognized after metagenomic analysis including the ferrous iron- and sulfur-oxidizing acidophilic genera Acidithiobacillus, Leptospirillum, Sulfobacillus and Ferroplasma. Mesophilic as well as moderately thermophilic acidophilic ferrous iron- and sulfur-oxidizing microorganisms were enriched from these samples and bioleaching was studied in shake flask experiments using a chalcopyrite-containing ore sample from the same mine. These enrichment cultures were further used as inoculum for bioleaching experiments in percolation columns for simulating heap bioleaching. Addition of 100 mM NaCl to the bioleaching medium was assessed to improve the dissolution rate of chalcopyrite. For comparison, bioleaching in stirred tank reactors with a defined microbial consortium was carried out as well. While just maximal 32% copper could be extracted in the flask bioleaching experiments, 73% and 76% of copper recovery was recorded after 30 and 10 days bioleaching in columns and bioreactors, respectively. Based on the results, both, the application of moderately thermophilic acidophilic bacteria in stirred tank bioreactors, and natural enrichment cultures of mesoacidophiles, with addition of 100 mM NaCl in column percolators with agglomerated ore allowed for a robust chalcopyrite dissolution and copper recovery from Sarcheshmeh copper ore via bioleaching.

Progress in bioleaching: fundamentals and mechanisms of bacterial metal sulfide oxidation--part A.

Bioleaching of metal sulfides is performed by a diverse group of microorganisms. The dissolution chemistry of metal sulfides follows two pathways, which are determined by the mineralogy and the acid solubility of the metal sulfides: the thiosulfate and the polysulfide pathways. Bacterial cells can effect this metal sulfide dissolution via iron(II) ion and sulfur compound oxidation. Thereby, iron(III) ions and protons, the metal sulfide-attacking agents, are available. Cells can be active either in planktonic state or in forming biofilms on the mineral surface; however, the latter is much more efficient in terms of bioleaching kinetics. In the case of Acidithiobacillus ferrooxidans, bacterial exopolymers contain iron(III) ions, each complexed by two uronic acid residues. The resulting positive charge allows an electrostatic attachment to the negatively charged pyrite. Thus, the first function of complexed iron(III) ions is the mediation of cell attachment, while their second function is oxidative dissolution of the metal sulfide, similar to the role of free iron(III) ions in non-contact leaching. In both cases, the electrons extracted from the metal sulfide reduce molecular oxygen via a redox chain forming a supercomplex spanning the periplasmic space and connecting both outer and inner membranes. In this review, we summarize some recent discoveries relevant to leaching bacteria which contribute to a better understanding of these fascinating microorganisms. These include surface science, biochemistry of iron and sulfur metabolism, anaerobic metabolism, and biofilm formation. The study of microbial interactions among multispecies leaching consortia, including cell-to-cell communication mechanisms, must be considered in order to reveal more insights into the biology of bioleaching microorganisms and their potential biotechnological use.

Microbial ecosystem assessment and hydrogen oxidation potential of newly discovered vent systems from the Central and South-East Indian Ridge.

In order to expand the knowledge of microbial ecosystems from deep-sea hydrothermal vent systems located on the Central and South-East Indian Ridge, we sampled hydrothermal fluids, massive sulfides, ambient water and sediments of six distinct vent fields. Most of these vent sites were only recently discovered in the course of the German exploration program for massive sulfide deposits and no previous studies of the respective microbial communities exist. Apart from typically vent-associated chemosynthetic members of the orders Campylobacterales, Mariprofundales, and Thiomicrospirales, high numbers of uncultured and unspecified Bacteria were identified via 16S rRNA gene analyses in hydrothermal fluid and massive sulfide samples. The sampled sediments however, were characterized by an overall lack of chemosynthetic Bacteria and the presence of high proportions of low abundant bacterial groups. The archaeal communities were generally less diverse and mostly dominated by members of Nitrosopumilales and Woesearchaeales, partly exhibiting high proportions of unassigned Archaea. Correlations with environmental parameters were primarily observed for sediment communities and for microbial species (associated with the nitrogen cycle) in samples from a recently identified vent field, which was geochemically distinct from all other sampled sites. Enrichment cultures of diffuse fluids demonstrated a great potential for hydrogen oxidation coupled to the reduction of various electron-acceptors with high abundances of Hydrogenovibrio and Sulfurimonas species. Overall, given the large number of currently uncultured and unspecified microorganisms identified in the vent communities, their respective metabolic traits, ecosystem functions and mediated biogeochemical processes have still to be resolved for estimating consequences of potential environmental disturbances by future mining activities.

Extracellular polymeric substances from Bacillus subtilis associated with minerals modify the extent and rate of heavy metal sorption.

Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral̀s ability to immobilize heavy metals. EPS from Bacillus subtilis were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb(2+), Cu(2+), and Zn(2+) to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal](total) = 50 µM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g(-1)) than ferrihydrite (7.9 mg g(-1)). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N(2) gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb(2+), Cu(2+), and Zn(2+) sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb(2+) > Cu(2+) > Zn(2+), which also prevailed in binary Pb(2+)/Cu(2+) systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites.

Prokaryotic cells of the deep sub-seafloor biosphere identified as living bacteria.

Chemical analyses of the pore waters from hundreds of deep ocean sediment cores have over decades provided evidence for ongoing processes that require biological catalysis by prokaryotes. This sub-seafloor activity of microorganisms may influence the surface Earth by changing the chemistry of the ocean and by triggering the emission of methane, with consequences for the marine carbon cycle and even the global climate. Despite the fact that only about 1% of the total marine primary production of organic carbon is available for deep-sea microorganisms, sub-seafloor sediments harbour over half of all prokaryotic cells on Earth. This estimation has been calculated from numerous microscopic cell counts in sediment cores of the Ocean Drilling Program. Because these counts cannot differentiate between dead and alive cells, the population size of living microorganisms is unknown. Here, using ribosomal RNA as a target for the technique known as catalysed reporter deposition-fluorescence in situ hybridization (CARD-FISH), we provide direct quantification of live cells as defined by the presence of ribosomes. We show that a large fraction of the sub-seafloor prokaryotes is alive, even in very old (16 million yr) and deep (> 400 m) sediments. All detectable living cells belong to the Bacteria and have turnover times of 0.25-22 yr, comparable to surface sediments.

Deltaproteobacterium Strain KaireiS1, a Mesophilic, Hydrogen-Oxidizing and Sulfate-Reducing Bacterium From an Inactive Deep-Sea Hydrothermal Chimney.

A novel deltaproteobacterial, mesophilic, hydrogen-oxidizing, and sulfate-reducing bacterium (strain KaireiS1) was highly enriched from an inactive chimney located in the active zone of the Kairei hydrothermal vent field (Central Indian Ridge) in the Indian Ocean. Based on 16S rRNA gene analyses, strain KaireiS1 is the currently only cultured representative of a cluster of uncultured Deltaproteobacteria, positioned within the Desulfobulbaceae family, between the Desulfobulbus genus and the "Cable Bacteria." A facultative autotrophic lifestyle of KaireiS1 is indicated by its growth in the absence of organic compounds, measurements of CO2-fixation rates, and activity measurements of carbon monoxide dehydrogenase, the key enzyme of the reductive Acetyl-CoA pathway. Apart from hydrogen, strain KaireiS1 can also use propionate, lactate, and pentadecane as electron donors. However, the highest cell numbers were reached when grown autotrophically with molecular hydrogen. Hydrogen uptake activity was found in membrane and soluble fractions of cell-free extracts and reached up to 2,981±129 nmol H2*min-1*mg-1 of partially purified protein. Commonly, autotrophic sulfate-reducing bacteria from the Deltaproteobacteria class, thriving in hydrothermal vent habitats are described as thermophiles. Given its physiological characteristics and specific isolation source, strain KaireiS1 demonstrates a previously unnoticed potential for microbial sulfate reduction by autotrophs taking place at moderate temperatures in hydrothermal vent fields.

Red mud regulates arsenic fate at acidic pH via regulating arsenopyrite bio-oxidation and S, Fe, Al, Si speciation transformation.

Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidans was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO2-based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals.