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Abstract: Microbial oxidation of ferrous iron may be available alternative method of producing ferric sulphate, which is a reagent used for removal of H2S from biogas. For practical use of this process, this study evaluated some of the most efficient bioreactor systems for continuous ferrous iron oxidation by iron-oxidizing bacteria. Performances of various bioreactor systems were compared based on the ferrous iron oxidation efficiency according to the stepwise increase of hydraulic loading rates and ease of operation. A submerged-membrane bioreactor and immobilized bioreactor systems were used to increase the cell concentration. In the immobilized bioreactor system, various support media such as a granular activated carbon, polyurethane foam and honeycomb-type ceramics were tested with respect to the cell immobilizing performance. To improve the stability of biofilm, airlift-type immobilized bioreactor system was also developed. In this study, both the membrane bioreactor system and the immobilized bioreactor system using polyurethane foam achieved very good performance of biological ferrous iron oxidation. However, in consideration of economical and operational aspects, the immobilized bioreactor using polyurethane foam is the most practical and efficient system for indirect H2S removal using iron-oxidizing bacteria. [Copyright &y& Elsevier]

Three acidophilic, chemolithotrophic and ferrous oxidizing bacteria were isolated from the Agrio River in the geothermal system of Copahue volcano in Neuquén (Patagonia, Argentina) using 9K enrichment medium and then purified on solid ferrous-agarose medium. Amplified ribosomal DNA restriction enzyme analysis (PCR/ARDRA) showed that these strains can be considered as Acidithiobacillus ferrooxidans. Ferrous iron oxidation of these strains, including a collection strain was compared at different temperatures (20, 25, 30, 35 and 40 °C) and pH values (1.6, 1.8 and 2.3). Isolated bacteria proved to be less susceptible to low temperatures or high medium acidity. These strains showed adequate growth in iron-free 9K medium using sulphur as a sole energy source. Iron(II) oxidation inhibition in the presence of different heavy metals (Ag+, Cd2+, Cu2+, Zn2+) or different anions (NO3-, Cl-) were also investigated. [Copyright &y& Elsevier]

Abstract: The relative abundance of two morphologically distinct iron-oxidizing bacteria (FeOB), in particular, helically stalked Gallionella ferruginea and sheathed Leptothrix ochracea, decreased downstream from a neutral pH groundwater spring that feeds Ogilvie Creek near Deep River, Ontario, Canada. Redox potential and dissolved oxygen increased with distance from the spring, whereas concentrations of ferrous and total iron decreased, dropping from 2.8 and 4.5 mg/l at the source to <0.5 mg/l 3.0 m downstream. Rates of ferrous iron oxidation measured in microcosms included (i) a chemical control with filtered spring water to assess the rate of inorganic chemical oxidation, (ii) a negative control containing 50 ml of sodium azide (0.1 M final concentration)-treated FeOB from the spring to evaluate the impact of bacteriogenic iron oxides on the chemical oxidation rate, and (iii) an experimental microcosm with 50 ml of live FeOB from the spring to ascertain the influence of FeOB on oxidation rates. The rate constant in the presence of FeOB (0.147 min−1) was 2.6 times greater than the sodium azide-treated FeOB (0.056 min−1) and 6.1 times greater than the chemical control (0.024 min−1). The change in chemical speciation of total iron in the microcosm systems over time indicated further that BIOS behave as potent substrates for ferric iron precipitation with up to 75% of the total iron precipitated after 25 min in the sodium azide treated and live FeOB microcosms, whereas only 30% of the total iron precipitated in the chemical control. [Copyright &y& Elsevier]

The Gram-negative iron-oxidizing bacterium Leptospirillum ferrooxidans contains all genes necessary for nitrogen fixation, from genes encoding the Mo–Fe nitrogenase, the specific regulator (nifA), global regulators like glnB and ntrC like genes, to other sensors and transport systems somehow related to nitrogen assimilation. We review current knowledge about the nif regulon and its connection with other metabolic functions in L. ferrooxidans. [Copyright &y& Elsevier]

A simple metabolic model of ferrous oxidizing bacteria based on biochemically structured balances of ATP and NAD(P)H is proposed in order to calculate maximum yield and maintenance on ATP. Similar values of growth yield and maintenance were obtained using data of ferrous iron and/or oxygen consumption in Acidithiobacillus ferrooxidans cultures on iron under different conditions. When pyrite was the sole energy source, growth yield was higher suggesting cells could obtain energy through the sulfur compounds oxidation. Values of growth yields for Leptospirillum ferrooxidans cultures on iron were a bit lower than those obtained for A. ferrooxidans although within the experimental errors. The maintenance coefficients on ATP for both bacteria were similar and comparable to those observed in heterotrophic microorganisms. This fact is really surprising taking in account the high proton gradient that this kind of microorganisms should maintain. [Copyright &y& Elsevier]

The effect of using FeS2 as an energy source, on the bioleaching of heavy metals (Zn, Cr, Cu, Pb and Ni) and nutrients (nitrogen and phosphorus) from anaerobically digested sludge using isolated indigenous iron-oxidizing bacteria was investigated in this paper. Addition of FeS2 in the range of 0.5–4.0 g l−1 accelerated the acidification of sludge and raised the oxidation–reduction potential of sludge medium with an inoculation of 15% (v/v) of active bacteria, thus resulting in an overall increase in metal dissolution efficiency. After 16 days of bioleaching at 28 °C and an initial pH of 3.0, up to 99% of Zn, 65% of Cr, 74% of Cu, 58% of Pb and 84% of Ni can be removed from the sludge. In contrast, only 94% of Zn, 12% of Cr, 21% of Cu, 32% of Pb and 38% of Ni were leached out in the control without inoculation of iron-oxidizing bacteria and the addition of FeS2. Less than 15% of nitrogen and 6% of phosphorous were lost after 16 days of bioleaching when using FeS2 as the energy source. Comparing to 39% and 45% loss respectively for these two nutrients when using FeSO4 · 7H2O as the energy source, FeS2 appears to be a more suitable energy source for preserving nutrients in sludge while removing heavy metals from sludge. [Copyright &y& Elsevier]

The combination of microbial reduction and further microbial oxidation of iron was applied to the treatment of food-processing wastewater and recovery of ammonium. Fe2+ ions were formed by iron-reducing bacteria under anaerobic conditions. Ammonium was recovered by co-precipitation with negatively charged iron hydroxides produced during oxidation of Fe2+ by iron-oxidizing bacteria under microaerophilic conditions. The value-added by-product of this process can be used as a slowly released ammonium fertilizer. [ABSTRACT FROM AUTHOR]

In the course of pilot industrial testing of a biohydrometallurgical technology for processing gold-arsenic concentrate obtained from the Nezhdaninskoe ore deposit (East Siberia, Sakha (Yakutiya)), a new gram-positive rod-shaped spore-forming moderately thermophilic bacterium (designated as strain N1) oxidizing Fe2+, S0, and sulfide minerals in the presence of yeast extract (0.02%) was isolated from a dense pulp. Physiologically, strain N1 differs from previously described species of the genus Sulfobacillus in having a somewhat higher optimal growth temperature (55°C). Unlike the type strain of S. thermosulfidooxidans, strain N1 could grow on a medium with 1 mM thiosulfate or sodium tetrathionate as a source of energy only within several passages and failed to grow in the absence of an inorganic energy source on media with sucrose, fructose, glucose, reduced glutathione, alanine, cysteine, sorbitol, sodium acetate, or pyruvate. The G+C content of the DNA of strain N1 was 48.2 mol %. The strain showed 42% homology after DNA–DNA hybridization with the type strain of S. thermosulfidooxidans and 10% homology with the type strain of S. acidophilus. The isolate differed from previously studied strains of S. thermosulfidooxidans in the structure of its chromosomal DNA (determined by the method of pulsed-field gel electrophoresis), which remained stable as growth conditions were changed. According to the results of the 16S rRNA gene analysis, the new strain forms a single cluster with the bacteria of the species Sulfobacillus thermosulfidooxidans (sequence similarity of 97.9–98.6%). Based on these genetic and physiological features, strain N1 is described as a new species Sulfobacillus sibiricus sp. nov. [ABSTRACT FROM AUTHOR]

Earlier, we described a new family of mesophilic, strictly autotrophic Fe2+-oxidizing archaebacteria, Ferroplasmaceae, which belongs to the order Thermoplasmales and includes the genus Ferroplasma and the species F. acidiphilum (strain YT) [1]. The present work is concerned with a comparative study of phenotypic characteristics of the type strain YТ and a new strain, F. acidiphilum Y-2, isolated from dense pulps during oxidation of gold-containing arsenopyrite/pyrite concentrates from the Bakyrchikskoe (Kazakhstan) and Olimpiadinskoe (Krasnoyarsk krai) ore deposits, respectively. The G+C content of DNA from strains YT and Y-2 comprised 35.1 and 35.2 mol %, respectively; the level of DNA–DNA homology between the strains was 84%. Restriction profiles of chromosomal DNA from both strains exhibited a similarity coefficient of 0.87. Genotypic characteristics of these strains indicate their affiliation to the same species. The cells of both strains are polymorphic and lack cell walls. Strains of F. acidiphilum oxidized ferrous iron and pyrite as the sole source of energy and fixed carbon dioxide as the sole carbon source. The strains required yeast extract as a growth factor. Optimum pH for cell growth ranged from 1.7 to 1.8; the temperature optima for the growth of strains YT and Y-2 were 34–36 and 40–42°С, respectively. Comparative analysis of the total lipids revealed their close similarity in the strains; two glycophospholipids comprised 90% of the total lipids: lipid I, β-D-glucopyranosylcaldarchaetidylglycerol (about 55%), and lipid II, trihexosylcaldarchaetidylglycerol (26%), whose isopranyl chains contained no cyclopentane rings. The carbohydrate fraction of lipid I hydrolysate contained only D-glucose, whereas hydrolysate of lipid II contained both D-glucose and D-galactose in a molar ratio of 2 : 1. Thus, it was established that the intraspecies phylogenetic divergence within F. acidiphilum is manifested in the two strains by different temperature optima against a background of similarity in other phenotypic properties. [ABSTRACT FROM AUTHOR]

Bioleaching has been demonstrated to be a feasible technology for removing heavy metals from sewage sludge, but the leaching medium needs to be pre-acidified to less than 4. The objective of the research presented in this paper was to investigate the pH requirement for isolated indigenous Thiobacillus ferrooxidans for bioleaching heavy metals from wastewater sludge in Hong Kong. Isolated sludge-indigenous iron-oxidizing bacteria were used for the bioleaching experiments to investigate the dissolution behaviour of heavy metals (Zn, Cu, Ni and Cr) from sludge set at an initial pH ranging from 3–7 with the purpose to reduce the acid consumption. The results showed that the inoculation of 15% of isolated indigenous iron-oxidizing bacteria and addition of 4.0 g L-1 Fe2+ (in the form of FeSO47H2O) resulted in a sharp decrease in sludge pH from an initial pH 3–7 to 2.1–2.4 and an increase in ORP (oxidation-reduction potential) from –200–38 mV to > 500 mV within the first 6 days. After 16 days of bioleaching, 50.2–78.4% of Cr, 63.7–74.1% of Cu, 74.9–88.2% of Zn and 15.5–38.6% of Ni can be leached out from the sludge at an initial pH range of 3–7. In contrast, only 1.5% of Cr, 1.7% of Cu, 15.3% of Zn and 15.5% of Ni was solubilized in the control run at pH 7.0. At the end of bioleaching, the dissolution of nutrients N and P from the organic matrix at pH 6 was significantly less than that at pH 3–5. Hence, the bioleaching efficiency could still be maintained at an initial pH of > 4 using the isolated indigenous T. ferrooxidans which would reduce the cost of operation. [ABSTRACT FROM AUTHOR]

Reddish filaments in two fragments of unusual iron oxide bearing stalactites, "the Rusticles" from Lechuguilla Cave, New Mexico, are found only within the central canals of the Rusticles. The curved, helical, and/or vibrioidal filaments vary from 1 to 6μm in outer diameter and 10 to > 50μm in length. SEM and TEM show the filaments have 0.5-μm diameter central tubes, with goethite crystals radiating outwardly along their lengths. The diameter of the central tubes is consistent with the diameter of many ironoxidizing filamentous bacteria. Although most iron oxide depositing bacteria do not deposit well-crystallized radiating goethite, we propose thick hydrous iron oxide was slowly crystallized from amorphous material to goethite, in place, over a relatively long period of time. From the gross morphology and the particular setting, we suggest this represents an occurrence of fossilized, acidophilic iron-oxidizing bacteria. [ABSTRACT FROM AUTHOR]

The deep-red lenses of the Pragian Slivenec Limestone have been extensively quarried for ornamental purposes since the XIIth century. Petrographic microscope observations indicate that the hematite stainings of the limestone follow ten different patterns. They range from massive non-directional filling of cavities to mineralized films and microstromatolites. Numerous ironrich endolithes are observed. Some could be derived from bacterial or lichen perforations and some related to ferric bacteria. Infiltration along welded calcite crystals, regular mineralized films and microstromatolites suggest a ferric bacterial origin for the pigment. This is confirmed by scanning microscope examinations of polished sections, that show hematite concentrations along micrometric filamentous sheaths. [ABSTRACT FROM AUTHOR]

Auriferous sulphide ores often incorporate micro-fine (or invisible) gold and silver particles in a manner making their extraction difficult. Nobel metals are lost in the tailings due to the refractory nature of these ores. Bioleaching is an environment-friendly alternative to the commonly used and toxic cyanidation protocols for gold extraction from refractory ores. In this paper, we investigate gold and silver bioleaching from porphyry and epithermal mineralisation systems, using iron-oxidizing bacteria Acidithiobacillus ferrooxidans. The invisible Au, sequestered in refractory ores, was characterised in situ by synchrotron micro X-Ray Fluorescence (SR-μ-XRF) and X-ray Absorption Spectroscopy (XAS), offering information on Au unaltered speciation at the atomistic level within the ore matrices and at a micro-scale spatial resolution. The SR-μ-XRF and XAS results showed that 10–20 μm sized elemental Au(0) nuggets are sequestered in pyrite, chalcopyrite, arsenopyrite matrices and at the interface of a mixture of pyrite and chalcopyrite. Moreover, the preliminary bioleaching experiments of the two types of ores, showed that Acidithiobacillus ferrooxidans can catalyse the dissolution of natural heterogeneous Fe-rich geo-matrices, sequestering Au and Ag and releasing particulate phases or partially solubilising them within 60 days. These results provide an understanding of noble metal sequestration and speciation within natural ores and a demonstration of the application of synchrotron-based micro-analysis in characterizing economic trace metals in major mineral structures. This work is a contribution to the ongoing efforts towards finding feasible and greener solutions of noble metal extraction protocols. Image 1 • Application of synchrotron in characterizing noble metals in mineral structures. • Au sequestration, spatial distribution and unaltered speciation within natural ores. • Bioleaching study using real Au ores and native, adapted iron-oxidizing bacteria. • IOB bio-oxidizes geo-matrixes leaching dissolved Ag and Au within 30–60 days. • Progress towards finding greener solutions of noble metals extraction technologies. [ABSTRACT FROM AUTHOR]

Natural attenuation in acid mine drainage (AMD) due to biological iron and arsenic oxidation offers a promising strategy to treat As-rich AMD in passive bioreactors. A reactive transport model is developed in order to identify the main controlling factors. It simulates batch and flow-through experiments that reproduce natural attenuation in a high-As AMD. The 2-D model couples second-order microbial kinetics (Fe- and As- oxidation) and geochemical reactions to hydrodynamic transport. Oxidation only occurrs in the biofilm with an oxygen transfer from the air through the water column. The model correctly simulates the Fe(II)-Fe(III) and As(III)-As(V) concentrations in the outlet waters and the precipitates, over hydraulic retention times from 30 min to 800 min. It confirms that the natural attenuation at 20 °C is driven by the fast Fe(II) oxidation and slow As(III) oxidation that favors arsenite trapping by schwertmannite over amorphous ferric arsenate (AFA) formation. The localization of iron oxidation in the biofilm limits the attenuation of arsenic and iron as the water column height increases. The change in the composition of the bacterial iron-oxidizer community of the biofilm at the lowest pH boundary seems to control the Fe(II) oxidation kinetic rate besides the bacterial concentration. ga1 • A reactive transport model for passive bioremediation of high-As acid mine drainage. • The 2-D model captures the oxygen transfer through water to the reactive biofilm. • Rate laws were obtained for microbial oxidation of Fe(II) and As(III) at different pH. • Schwertmannite precipitation plays a key role on pH decrease and arsenite scavenging. • Composition of the iron-oxidizing bacterial community controlled Fe(II) oxidation rate. [ABSTRACT FROM AUTHOR]

Groundwater in several parts of the world, particularly in developing countries, has been contaminated with Arsenic (As). In search of low-cost As removal methods, the biological oxidation of As(III) and Fe(II) followed by co-precipitation requires detailed investigation for the practical implementation of this technology. The present study investigated the biological oxidation of As(III) and Fe(II) through a combination of laboratory experiments and reactive transport modeling. Batch experiments were conducted to evaluate the As(III) oxidation by Fe-oxidizing bacteria, mainly Leptothrix spp. A fixed-bed down-flow biological column containing inexpensive and readily available coconut husk support media was used to evaluate the combined removal of As(III) and Fe(II) from synthetic groundwater. Oxidation and co-precipitation processes effectively reduced the concentration of As(III) from 500 μg/L to < 10 μg/L with a hydraulic retention time of 120 min. A one-dimensional reactive transport model was developed based on the microbially mediated biochemical reactions of As(III) and Fe(II). The model successfully reproduced the observed As(III) and Fe(II) removal trends in the column experiments. The modeling results showed that the top 20 cm aerobic layer of the column played a primary role in the microbial oxidation of Fe(II) and As(III). The model calibration identified the hydraulic residence time as the most significant process parameter for the removal of Fe and As in the column. The developed model can effectively predict As concentrations in the effluent and provide design guidelines for the biological treatment of As. The model would also be useful for understanding the biogeochemical behavior of Fe and As under aerobic conditions. Image 1 • Oxidation and co-precipitation of As(III) and Fe(II) by iron oxidizing bacteria. • Efficient removal (>98%) of As(III) and Fe(II) achieved in biological column. • A reactive transport model successfully simulated the biological As(III) removals. • As(III) and Fe(II) oxidation was mediated in BioPhase. • Metabolic products, i.e., Fe(OH) 3 and As(V), co-precipitated in the matrix phase. Biological column containing coconut husk media is able to remove As(III) to below 10 μg/L through biological oxidation and co-precipitation process. The reactive transport model successfully reproduced the observed As(III) and Fe(II) removal trends of the column experiments. [ABSTRACT FROM AUTHOR]

The redox cycle of iron (Fe) is a key process in the biogeochemistry of paddy field soil. It has been recently remarked that Fe(II)-oxidizing bacteria belonging to the family Gallionellaceae (Gallionella -related FeOB) are one of the key players in the Fe(II) oxidation in the soil. The present study aimed to investigate the influence of alternate wetting and drying (AWD) irrigation for water-saving rice cultivation on the dynamics of the community of Gallionella -related FeOB in the paddy field soil over three seasons (wet-dry-wet seasons) of rice cultivation. The AWD irrigation brought about the reduction of Fe(II) contents in the soil, compared with the continuously flooding (CF) irrigation, especially in the last half of the rice cultivation period in the dry season. In contrast, a trend of higher copy number of 16S rRNA genes of Gallionella -related FeOB was observed in the last half of the rice cultivation period of the AWD paddy soil. As a result, a significant negative correlation was observed between the Fe(II) contents and the copy numbers of 16S rRNA genes. PCR-DGGE analysis of 16S rRNA genes of Gallionella -related FeOB showed that the band patterns were different between the CF and AWD paddy soils. Meanwhile, the results of clone library analysis indicated that differences in the taxonomic composition of Gallionella -related FeOB were not observed between the CF and AWD paddy soils, suggesting that Gallionella -related FeOB responded to the AWD water-saving irrigation on the individual strain levels. The potential of Fe(II)-oxidizing activity and its apparent contribution of the activity of Gallionella -related FeOB to the Fe(II) oxidation in the soil of the investigated field were estimated to be 2.4 × 10−3 to 1.7 × 10−1 mg Fe(II) g−1 dry soil day−1 and 4.6%, respectively, based on the reported Fe(II) oxidation rates of cells. The present study showed that the fluctuation of the redox status of Fe caused by the repeated cycle of wetting and drying of the field brought about the changes in the community structure of Gallionella -related FeOB in the soil. Furthermore, it was suggested that Gallionella -related FeOB were certainly involved in the Fe(II)-oxidizing process in the AWD paddy field soil. • This study focused on Gallionella -related Fe(II)-oxidizing bacteria (FeOB). • AWD irrigation influenced the community structure of Gallionella -related FeOB. • Their abundances negatively correlated with the Fe(II) contents in the soil. • Their estimated contribution to the soil Fe(II) oxidation was 4.6%. [ABSTRACT FROM AUTHOR]

Iron-redox cycling microorganisms are important for understanding the biogeochemical iron and play key roles in zero-valent iron (ZVI) mediated environmental bioremediation. Their influence on ZVI oxidation coupling with organic contaminant removal is of particular interest but is still poorly understood. The objective of this research was to study microbial redox cycles of iron in ZVI oxidation and deca-brominated diphenyl ether (deca-BDE) removal. It was found that iron-oxidizing bacteria (IOB) enhanced ZVI oxidation by using iron as the sole electron donor. Iron-reducing bacteria (IRB) with high activity of Fe (III) reduction, also significantly accelerated rather than inhibited ZVI oxidation. ZVI oxidation activity was increased from 3.42% to 24.28% by IOB and 19.49% by IRB. When deca-BDE was present in the medium, ZVI oxidation activity by IOB and IRB was increased from 2.67% to 48.33% and 64.33%, respectively. However, no co-accelerating effect of IOB and IRB occurred but rather a neutralizing influence on ZVI oxidation was detected with iron-redox cycling bacteria (IORB). ZVI oxidation activity by IORB only increased to 13.14% and 37.0% in the absence and presence of deca-BDE, respectively. Meanwhile, IRB also exhibited the highest removal activity of deca-BDE. Approximately 71.67% of deca-BDE was removed by IRB, compared to 18.91% by IOB and 43.24% by IORB. Deca-BDE significantly influenced the effects of iron-metabolizing microorganisms on ZVI oxidation by altering the composition of microbial communities. Pseudomonas , Paenibacillus , and Sporolactobacillus were the key genera influencing ZVI oxidation and deca-BDE removal. Sporolactobacillus was firstly reported to be able to stimulate both ZVI oxidation and deca-BDE removal. Pseudomonas accelerated ZVI oxidation but had no significant contribution to deca-BDE removal. However, Paenibacillus inhibited both Fe(III) reduction and deca-BDE removal. It is expected that continuous integration of ZVI oxidation and organic contaminant removal can be achieved by regulating the key genera in iron-metabolizing microbial communities. Unlabelled Image • Zero-valent iron oxidation and deca-brominated diphenyl ether removal were studied. • Iron-metabolizing microbes enhanced ZVI oxidation coupling with deca-BDE removal. • Effects of iron-redox cycling bacteria on ZVI oxidation were independent of deca-BDE. • Deca-BDE significantly influenced the effects of IOB and IRB on ZVI oxidation. • Pseudomonas , Paenibacillus , and Sporolactobacillus were found to be the key genera. [ABSTRACT FROM AUTHOR]

• Sb(V) was efficiently removed using scrap iron inoculated with SRB and IOB. • Generation of biogenetic iron oxides could provide favorable condition for SRB. • 80.35% of Sb(V) was adsorbed, and 19.65% was bio-reduced as Sb 2 S 3. • Per gram of iron in bioreactor can remove180 mg of Sb after running for 310 days. Treatment of antimony (Sb) mine drainage is generally regarded as a priority issue for regulatory authorities. In the study synergetic removal of Sb(V) from wastewater using cheap scrap iron inoculated with iron-oxidizing bacteria (IOB) and sulfate-reducing bacteria (SRB) was proposed. A strain of Enterobacter sp. (named as IOB-L), and Desulfovibrio sp. (named as GSRB) was first isolated separately, and Sb(V) removal performance in four different systems were investigated through batch experiment. It demonstrated that after 168 h of reaction, Sb(V) removal efficiency in iron + IOB + SRB system was 99.98%, which was higher than that in pure scrap iron, iron + IOB, and SRB system. SEM-EDX, XRD, and XPS analysis of reaction products indicated that scrap iron could be oxidized to amorphous Fe 2 O 3 and FeOOH completely in biotic systems, providing favorable anaerobic condition for SRB. At the end of experiment, 80.35% of Sb(V) in iron + IOB + SRB system was adsorbed by biogenetic iron oxides, and 19.65% was bio-reduced as Sb 2 S 3. Moreover, long-term treatment of antimony mine wastewater by scrap iron inoculated with IOB and SRB increased the bacterial abundance in the bioreactor, and Sb(V) removal ability of iron reached 180 mg(Sb)/g (Fe) after running for 310 days. The study provides an efficient method to remove Sb(V) from mine wastewater and might open a new way for the application of iron fillings. [ABSTRACT FROM AUTHOR]

Disposing of low-grade ores involves numerous environmental issues. Bioleaching with acidophilic bacteria is the preferred solution to process these ores for metals recovery. In this study, indigenous iron-oxidizing bacteria Acidithiobacillus ferrooxidans , Leptospirillum ferriphilum , and Leptospirillum ferrooxidans were used in consortia supplemented with acid-treated bamboo sawdust (BSD) for copper and zinc recovery. Findings showed the extreme catalytic response of BSD with the best recovery of metals. Maximum of 92.2 ± 4.0% copper (0.35%) and 90.0 ± 5.4% zinc (0.33%) were recovered after 8 days of processing in the presence of 2 g/L BSD. Significant variations were reported in physicochemical parameters during bioleaching in the presence of a different concentration of BSD. Fourier Transform Infrared spectroscopy results of bioleached residues showed significant variations in spectral pattern and maximum variations were reported in 2.0 g/L BSD, which indicates maximum metals dissolutions. The impact of bacterial consortia and BSD on iron speciation of bioleached ores was analyzed by using Mössbauer spectroscopy and clear variations in iron speciation were reported. Furthermore, the bacterial community structure dynamics revealed significant variations in the individual bacterial proportion in each experiment. This finding shows that the dosage concentration of BSD influenced the microenvironment, which effect the bacterial abundance and these variations in the bacterial structural communities were not associated with the initial proportion of bacterial cells inoculated in the bioleaching process. Moreover, the mechanism of chemical reactions was proposed by explaining the possible role of BSD as a reductant under micro-aerophilic conditions that facilitates the bacterial reduction of ferric iron. This type of bioleaching process with indigenous iron-oxidizing bacteria and BSD has significant potential to further upscale the bioleaching process for recalcitrant ore bodies in an environment friendly and cost-effective way. Unlabelled Image • Bioleaching of low-grade ore added with bamboo sawdust boosted the metals recovery. • Bamboo sawdust acted as a reductant and a low cost reagent during bioleaching. • Analytical characterization of bioleaching media showed significant variations. • Bamboo sawdust significantly influenced the bacterial diversity in the process. • This method offers an effective bioprocessing of low-grade ores. [ABSTRACT FROM AUTHOR]

Fe, Si-rich low-temperature hydrothermal precipitates, typical hydrothermal products of low-temperature diffuse flow, have been found widely on the seafloor. It is believed that microorganisms play an important role in the formation of Fe, Si-rich low-temperature precipitates, yet, microbial biomineralization within these precipitates has not been well understood. In this study, we characterized different hydrothermal precipitates collected from the Lau Basin of the western Pacific Ocean, using an integrated mineralogical, geochemical, ultrastructural and microbiological approach. Three types of Fe, Si-rich precipitates were identified: Fe-rich, Fe–Si-rich and Si-rich, consisting of amorphous or poor crystalline minerals, from the two-line ferrihydrite to opal-A. Geochemical indices suggest that the precipitates are typical low-temperature hydrothermal origin, precipitated from mixing, at various extent, of hydrothermal fluid and seawater. All three types of Fe, Si-rich precipitates show abundant and distinctive biogenic ultrastructures, indicating different biomineralization experiences. The Fe-rich precipitates dominantly exhibited the typical Fe-enriched ultrastructures produced by putative iron-oxidizing bacteria (FeOB), suggesting the prevalence of Fe-oxidation catalyzed by FeOB in its formation process. Similar FeOB-catalyzed biomineralization process also happened in Fe–Si-rich precipitates with the abundant occurrence of FeOB-induced ultrastructures. By contrast, the Si-enriched architectures, encompassing mycelium-like networks, became absolutely prevailing within Si-rich precipitates. Based on their indicative morphologies, mycelium-like networks were ascribed as silicified actinobacteria or fungi, suggesting that silicification induced by actinobacteria or fungi dominated the biomineralization process. Microbiological analysis revealed the existence of a series of diverse, heterogeneous microbial populations within different Fe, Si-rich precipitates. However, no putative FeOB lineages were detected in the Fe-rich and Fe–Si-rich precipitates. Taken together, our results indicate that different biomineralization processes induced by different microbial lineages contributed to the formation of the three different types of Fe, Si-rich precipitates and the distinct environmental conditions existed for heterogeneous microorganisms within these different Fe, Si-rich precipitates. • Biomineralization of different Fe, Si-rich hydrothermal precipitates is characterized. • Different types of biogenic ultrastructures were distinguished and described. • Heterogeneous, diverse bacterial lineages were revealed within different precipitates. [ABSTRACT FROM AUTHOR]

Freshwater iron mats are dynamic geochemical environments with broad ecological diversity, primarily formed by the iron-oxidizing bacteria. The community features functional groups involved in biogeochemical cycles for iron, sulfur, carbon, and nitrogen. Despite this complexity, iron mat communities provide an excellent model system for exploring microbial ecological interactions and ecological theories in situ Syntrophies and competition between the functional groups in iron mats, how they connect cycles, and the maintenance of these communities by taxons outside bacteria (the eukaryota, archaea, and viruses) have been largely unstudied. Here, we review what is currently known about freshwater iron mat communities, the taxa that reside there, and the interactions between these organisms, and we propose ways in which future studies may uncover exciting new discoveries. For example, the archaea in these mats may play a greater role than previously thought as they are diverse and widespread in iron mats based on 16S rRNA genes and include methanogenic taxa. Studies with a holistic view of the iron mat community members focusing on their diverse interactions will expand our understanding of community functions, such as those involved in pollution removal. To begin addressing questions regarding the fundamental interactions and to identify the conditions in which they occur, more laboratory culturing techniques and coculture studies, more network and keystone species analyses, and the expansion of studies to more freshwater iron mat systems are necessary. Increasingly accessible bioinformatic, geochemical, and culturing tools now open avenues to address the questions that we pose herein., (Copyright © 2020 Brooks and Field.)

This study reports on the effect of inoculum history, growth substrates, and yeast extract on sodium chloride tolerance of Sulfobacillus thermosulfidooxidans DSM 9293 T . The concentrations of NaCl for complete inhibition of Fe 2+ oxidation by cells initially grown with ferrous iron sulfate, or tetrathionate, or pyrite as energy sources were 525 mM, 725 mM, and 800 mM, respectively. Noticeably, regardless of NaCl concentrations, oxygen consumption rates of S. thermosulfidooxidans with 20 mM tetrathionate were higher than with 50 mM FeSO 4 . NaCl concentrations of higher than 400 mM strongly inhibited the iron respiration of S. thermosulfidooxidans. In contrast, the presence of NaCl was shown to stimulate tetrathionate oxidation. This trend was especially pronounced in NaCl-adapted cells where respiration rates at 200 mM NaCl were threefold of those in the absence of NaCl. In NaCl-adapted cultures greater respiration rates for tetrathionate were observed than in non-NaCl-adapted cultures, especially at concentrations ≥ 200 mM NaCl. At concentrations of ≤ 200 mM NaCl, cell growth and iron oxidation were enhanced with the addition of increasing concentrations of yeast extract. Thus, cell numbers in cultures with 0.05% yeast extract were ∼5 times higher than without yeast extract addition. At NaCl concentration as high as 400 mM, however, iron oxidation rates improved compared to control assays without yeast extract, but there was no clear dependence on yeast extract concentrations. The initial growth of bacteria with and without yeast extract in the presence of different NaCl concentrations was shown to impact leaching of copper from chalcopyrite. Copper dissolution was enhanced in the presence of 200 mM NaCl and absence of yeast extract, while the addition of 0.02% yeast extract was shown to promote copper solubilization in the presence of 500 mM NaCl., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

Shipwrecks act as artificial reefs and provide a solid surface in aquatic systems for many different forms of life to attach to, especially microbial communities, making them a hotspot of biogeochemical cycling. Depending on the microbial community and surrounding environment, they may either contribute to the wreck's preservation or deterioration. Even within a single wreck, preservation and deterioration processes may vary, suggesting that the microbial community may also vary. This study aimed to identify the differences through widespread sampling of the microbial communities associated with the Pappy Lane shipwreck (NC shipwreck site #PAS0001), a shallow water ferrous-hulled shipwreck in Pamlico Sound, North Carolina to determine if there are differences across the wreck as well as from its surrounding environment. Loose shipwreck debris, drilled shipcores, surrounding sediment, and seawater samples were collected from the Pappy Lane shipwreck to characterize the microbial communities on and around the shipwreck. Results indicated that the shipwreck samples were more similar to each other than the surrounding sediment and aquatic environments suggesting they have made a specialized niche associated with the shipwreck. There were differences between the microbial community across the shipwreck, including between visibly corroded and non-corroded shipwreck debris pieces. Relative abundance estimates for neutrophilic iron-oxidizing bacteria (FeOB), an organism that may contribute to deterioration through biocorrosion, revealed they are present across the shipwreck and at highest abundance on the samples containing visible corrosion products. Zetaproteobacteria , a known class of marine iron-oxidizers, were also found in higher abundance on shipwreck samples with visible corrosion. A novel Zetaproteobacteria strain, Mariprofundus ferrooxydans O1, was isolated from one of the shipwreck pieces and its genome analyzed to elucidate the functional potential of the organism. In addition to iron oxidation pathways, the isolate has the genomic potential to perform carbon fixation in both high and low oxygen environments, as well as perform nitrogen fixation, contributing to the overall biogeochemical cycling of nutrients and metals in the shipwreck ecosystem. By understanding the microbial communities associated with shallow water ferrous-hulled shipwrecks, better management strategies and preservation plans can be put into place to preserve these artificial reefs and non-renewable cultural resources., (Copyright © 2020 Price, Garrison, Richards and Field.)

The pharmaceutical and hygienic productivity of wastewater containing pollutants, especially heavy metals such as nickel, andmercury are brought into the nature. Recently, bio-removal of heavy metals has attracted significant attention as an eco-friendly approach for the research departments of the pharmaceutical companies. In the current study, removal of heavy metals including mercury and nickel was assessed using isolatediron-oxidizing bacteria from different sources. To this end, bacterial populations were isolated from a variety of aquatic ecosystems; including Mahallat Pond, mountainous rivers, iron industry wastewater, and treated industrial wastewater. The bacteria were cultured and purified in iron-oxidizing media after which the removal of mercury and nickel was measured through culturing the isolated bacteria in 3 different media of Luria-Bertani, PHGII, and iron-oxidizing media containing the heavy metals (2 ppm). The results proved LB as a suitable medium for all the isolated bacteria in removing the heavy metals.It was shown that approximately 100% of the mercury was removed through the bacterial cultured in LB medium. The removal of nickel also reached its maximum of 30% by bacterial culture in LB medium. Then, the phylogenetic study according to 16S rDNA gene sequences showed thatthe isolated bacteria from iron industry wastewater was Bacillus velezensis CR-502 (T).In summary, this study demonstrated the impressive ability of these bacteria for mercury removal and theeffects of different mediaon the removal of mercury and nickel.

Possibilities for the recovery of non-ferrous and precious metals from Kapan polymetallic mine tailings (Armenia) were studied. The aim of this paper was to study the possibilities of bioleaching of samples of concentrated tailings by the natural microbial consortium of drainage water. The extent of extraction of metals from the samples of concentrated tailings by natural microbial consortium reached 41-55% and 53-73% for copper and zinc, respectively. Metal leaching efficiencies of pure culture Leptospirillum ferrooxidans Teg were higher, namely 47-93% and 73-81% for copper and zinc, respectively. The content of gold in solid phase of tailings increased about 7-16% and 2-9% after bio-oxidation process by L. ferrooxidans Teg and natural microbial consortium, respectively. It was shown that bioleaching of the samples of tailings could be performed using the natural consortium of drainage water. However, to increase the intensity of the recovery of valuable metals, natural consortium of drainage water combined with iron-oxidizing L. ferrooxidans Teg has been proposed.

Iron-oxidizing bacteria (FeOB) are some of the initial colonizing organisms during microbially influenced corrosion of steel infrastructure. To better understand the abiotic conditions under which FeOB colonize steel, an environmental study was conducted to determine the effects of salinity, temperature, dissolved oxygen levels, and steel type on FeOB colonization. Stainless steel (304 and 316 [i.e., 304SS and 316SS]) was used to determine the potential susceptibility of these specialized corrosion-resistant steels. Steel coupon deployments along salinity gradients in two river systems revealed attachment by FeOB at all sites, with greater abundance of FeOB at higher salinities and on 316SS, compared to 304SS. This may be due to the presence of molybdenum in 316SS, potentially providing a selective advantage for FeOB colonization. A novel Zetaproteobacteria species, Mariprofundus erugo , was isolated from these stainless steel samples. Genes for molybdenum utilization and uptake and reactive oxygen species protection were found within its genome, supporting the evidence from our FeOB abundance data; they may represent adaptations of FeOB for colonization of surfaces of anthropogenic iron sources such as stainless steel. These results reveal environmental conditions under which FeOB colonize steel surfaces most abundantly, and they provide the framework needed to develop biocorrosion prevention strategies for stainless steel infrastructure in coastal estuarine areas. IMPORTANCE Colonization of FeOB on corrosion-resistant stainless steel types (304SS and 316SS) has been quantified from environmental deployments along salinity gradients in estuarine environments. Greater FeOB abundance at higher salinities and on the more-corrosion-resistant 316SS suggests that there may be a higher risk of biocorrosion at higher salinities and there may be a selective advantage from certain stainless steel alloy metals, such as molybdenum, for FeOB colonization. A novel species of FeOB described here was isolated from our stainless steel coupon deployments, and its genome sequence supports our environmental data, as genes involved in the potential selectiveness toward surface colonization of stainless steel might lead to higher rates of biocorrosion of manmade aquatic infrastructure. These combined results provide environmental constraints for FeOB colonization on anthropogenic iron sources and build on previous frameworks for biocorrosion prevention strategies., (Copyright © 2019 American Society for Microbiology.)

Challenges to the reclamation of pyritic mine tailings arise from in situ acid generation that severely constrains the growth of natural revegetation. While acid mine drainage (AMD) microbial communities are well-studied under highly acidic conditions, fewer studies document the dynamics of microbial communities that generate acid from pyritic material under less acidic conditions that can allow establishment and support of plant growth. This research characterizes the taxonomic composition dynamics of microbial communities present during a 6-year compost-assisted phytostabilization field study in extremely acidic pyritic mine tailings. A complementary microcosm experiment was performed to identify successional community populations that enable the acidification process across a pH gradient. Taxonomic profiles of the microbial populations in both the field study and microcosms reveal shifts in microbial communities that play pivotal roles in facilitating acidification during the transition between moderately and highly acidic conditions. The potential co-occurrence of organoheterotrophic and lithoautotrophic energy metabolisms during acid generation suggests the importance of both groups in facilitating acidification. Taken together, this research suggests that key microbial populations associated with pH transitions could be used as bioindicators for either sustained future plant growth or for acid generation conditions that inhibit further plant growth.

Biogenic iron(III) minerals (BIM) widely occur in aquatic systems. However, characteristics and mechanisms of As sequestration by biogenic biphasic Fe(III) minerals (Bio-bi-minerals) are not clearly understood. We investigated characteristics of Bio-bi-minerals induced by Pseudogulbenkiania sp. strain 2002 and explored their As sequestration mechanisms by monitoring particle morphology, mineralogical composition, and As binding properties. Results showed that Fe(II) oxidation (about 3 mM) by Pseudogulbenkiania sp. strain 2002 under growth condition produced biogenic ferrihydrite-goethite biphasic Fe(III) minerals (Fh-Gt Bio-bi-minerals), which showed better performance in As immobilization compared to corresponding biogenic monophasic Fe(III) minerals (Bio-mono-minerals). Decreased particle size, increased abundance of ferrihydrite and occurrence of bidentate mononuclear edge-sharing ( 2 E) and monodentate mononuclear edge-sharing As complexes ( 1 V) contributed to enhanced As immobilization by Fh-Gt Bio-bi-minerals. We suggest that the Bio-bi-minerals have the potential to illuminate As biogeochemical cycles in aquatic systems and to remediate As and nitrate co-contaminated groundwater., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Terraced iron formations (TIFs) are laminated structures that cover square meter-size areas on the surface of weathered bench faces and tailings piles at the Mount Morgan mine, which is a non-operational open pit mine located in Queensland, Australia. Sampled TIFs were analyzed using molecular and microanalytical techniques to assess the bacterial communities that likely contributed to the development of these structures. The bacterial community from the TIFs was more diverse compared to the tailings on which the TIFs had formed. The detection of both chemolithotrophic iron-oxidizing bacteria, i.e., Acidithiobacillus ferrooxidans and Mariprofundus ferrooxydans, and iron-reducing bacteria, i.e., Acidobacterium capsulatum, suggests that iron oxidation/reduction are continuous processes occurring within the TIFs. Acidophilic, iron-oxidizing bacteria were enriched from the TIFs. High-resolution electron microscopy was used to characterize iron biomineralization, i.e., the association of cells with iron oxyhydroxide mineral precipitates, which served as an analog for identifying the structural microfossils of individual cells as well as biofilms within iron oxyhydroxide laminations—i.e., alternating layers containing schwertmannite (Fe16O16(OH)12(SO4)2) and goethite (FeO(OH)). Kinetic modeling estimated that it would take between 0.25–2.28 years to form approximately one gram of schwertmannite as a lamination over a one-m2 surface, thereby contributing to TIF development. This length of time could correspond with seasonable rainfall or greater than average annual rainfall. In either case, the presence of water is critical for sustaining microbial activity, and subsequently iron oxyhydroxide mineral precipitation. The TIFs from the Mount Morgan mine also contain laminations of gypsum (CaSO·2H2O) alternating with iron oxyhydroxide laminations. These gypsum laminations likely represented drier periods of the year, in which millimeter-size gypsum crystals presumably precipitated as water gradually evaporated. Interestingly, gypsum acted as a substrate for the attachment of cells and the growth of biofilms that eventually became mineralized within schwertmannite and goethite. The dissolution and reprecipitation of gypsum suggest that microenvironments with circumneutral pH conditions could exist within TIFs, thereby supporting iron oxidation under circumneutral pH conditions. In conclusion, this study highlights the relationship between microbes for the development of TIFs and also provides interpretations of biogeochemical processes contributing to the preservation of bacterial cells and entire biofilms under acidic conditions. [ABSTRACT FROM AUTHOR]

Bacterial–mineral aggregates are the products of a tight biogeochemical coupling between microbes and geological media and play an outsized role in governing the composition of natural waters through biogeochemical cycling and mineral formation and dissolution processes. The results of combined batch column settling experiments, volumetric analyses, and microscopic investigations demonstrate that composite bacteriogenic iron oxide aggregates are sensitive to densification in response to hydrodynamic shear, a physical fluid phenomenon that introduces significant alterations to aggregate size and structure, permeability, and settling and transport behaviour. After exposing aggregate suspensions to varying degrees of shear stress, final solids volume fractions decreased by as much as 75% from initial data, while aggregate bulk density saw increases from 999 kg·m–3 to as much as 1010 kg·m–3. Inverse modelling of time course data yielded estimates for settling rate constants and initial settling velocities that increased with shear stress application. As well as having implications for aqueous contaminant transport and potential bacterial bioenergetic strategies, these results suggest the preservation potential of microfossils formed from bacterial–mineral aggregates may be significantly reduced with shear-induced alterations, leading to a possible underrepresentation of these microfossils in the sedimentary record and a gap in our understanding of early life on Earth. [ABSTRACT FROM AUTHOR]