Sulfur-oxidizing Microorganisms Research Articles

Chemolithoautotrophic bacteria flourish at dark water-ice interfaces of an emerged Arctic cold seep.

Below their ice shells, icy moons may offer a source of chemical energy that could support microbial life in the absence of light. In the Arctic, past and present glacial retreat leads to isostatic uplift of sediments through which cold and methane-saturated groundwater travels. This fluid reaches the surface and freezes as hill-shaped icings during winter, producing dark ice-water interfaces above water ponds containing chemical energy sources. In one such system characterized by elevated methane concentrations - the Lagoon Pingo in Adventdalen, Svalbard (~10mg/L CH4, <0.3mg/L O2, -0.25°C, pH7.9), we studied amplicons of the bacterial and archaeal (microbial) 16S rRNA gene and transcripts in the water pond and overlaying ice. We show that active chemolithoautotrophic sulfur-oxidizing microorganisms (Sulfurimonas, Thiomicrorhabdus) dominated a niche at the bottom of the ice in contact with the anoxic water reservoir. There, the growing ice offers surfaces interfacing with water, and hosts favorable physico-chemical conditions for sulfide oxidation. Detection of anaerobic methanotrophs further suggests that the ice led to a steady-state dark and cold methane sink under the ice throughout winter, in two steps: first methane is oxidized to carbon dioxide and sulfates concomitantly reduced to sulfides by the activity of ANME-1a and SEEP-SRB1 consortia, in a second time energy from sulfides is used by sulfur- oxidizing microorganisms to fix carbon dioxide into organic carbon. Our results underline ice- covered and dark ecosystems as a hitherto overlooked oasis of microbial life and emphasize the need to study microbial communities in icy habitats.

Exploring Biodiversity and Food Webs in Sulfur Cave in the Vromoner Canyon on the Greek–Albanian Border

Sulfidic caves support diverse and abundant subterranean communities, including numerous endemic species and complex food webs, though the full extent of species diversity and resource utilization in these ecosystems remains largely unexplored. This paper presents the results of biological surveys conducted from 2023 to 2024 in Sulfur Cave, located in the Vromoner Canyon on the Greek–Albanian border, focusing on microbial, vertebrate, and invertebrate communities and investigating the structure of the subterranean food web. The microbial communities from the different biofilms are dominated by chemosynthetic sulfur-oxidizing microorganisms, specifically filamentous bacteria such as Thiotrix and Beggiatoa. Two species of fish, an eel (Anguilla sp.) and a Cyprinid (Alburnoides sp.), and six bat species from three families (Rhinolophidae, Miniopteridae, and Vespertilionidae) were documented. The invertebrate fauna includes five aquatic species, 25 terrestrial species, and four amphibiotic species. Among these, eight species are endemic, and seven species exhibit troglomorphic traits. Stable isotope analysis showed light carbon and nitrogen values for the terrestrial and aquatic invertebrates, suggesting that subterranean communities rely on food produced in situ by chemoautotrophic microorganisms. Our results identified cave areas of significant biological relevance and provided reference data to inform conservation actions aimed at preserving the biodiversity of this sulfidic cave.

Effects of Pyrolysis Temperature on Biochar Physicochemical and Microbial Properties for H2S Removal from Biogas

Sludge is produced in sewage treatment plants and is still a problematic waste type after anaerobic digestion. A sustainable sludge management strategy would be to pyrolyze it and obtain biochar suitable for use in biofilters. This article examines the physical and chemical properties of biochar obtained by pyrolyzing sewage sludge at a temperature of 300–600 °C. The pyrolyzed sludge was used in the biofilter as a filler. The results demonstrated biochar packing materials after pyrolysis at 300 °C, 400 °C, 500 °C, and 600 °C, which exhibited porosities of 35%, 42%, 67%, and 75%, respectively. During the research study, it was established that the biofilter showed excellent efficiency (between 55 and 99 percent) when using carbon pyrolyzed at temperatures of 500 °C and 600 °C. In this study, the average growth rates of the number of sulfur-oxidizing microorganisms were 1.55 × 104 CFU/g at the first stage of the biofilter, 2.63 × 104 CFU/g at the second stage, 3.65 × 104 CFU/g at the third stage, 5.73 × 104 CFU/g at the fourth stage, and 2.62 × 104 CFU/g at the fifth stage. The number of sulfur-oxidizing microorganisms in the packing bed of biofilters during the 60-day period of the experiment constantly increased. The experimental results of H2S purification in biogas were compared with mathematical modeling results. These comparative results revealed a consistent trend: the model-estimated filter efficiency also reached 70–90 percent after 60 days of investigation.

Enhanced degradation of methanethiol via operational pH regulation in biofilm reactor: Insight of sulfur metabolism pathways and microbial adaptation mechanism

Methanethiol (CH3SH), a typical organic sulfur pollutant, poses significant risks to both human health and ecological stability due to its high toxicity and corrosive properties. Membrane aerated biofilm reactor (MABR) has been regarded as a promising and eco-friendly solution for removing organic sulfur from wastewater. However, the oxidation of CH3SH might lead to spontaneous acidification, which might affect microbial metabolic activities to influence the CH3SH biotransformation in MABR system. This work demonstrated that operational pH regulation could effectively promote the complete conversion of CH3SH to SO42- in MABR, while the transformation efficiency was only 40.6% under uncontrolled pH condition. Meanwhile, operational pH regulation resulted in 35.2% reduction in the excessive secretion of extracellular polymeric substances, thereby building a stable biofilm structure with sufficient oxygen mass transfer to enhance the CH3SH transformation. Additionally, operational pH regulation favored the enrichment of sulfur-oxidizing microorganisms (e.g., Rhodanobacter and Rhodobacter), while the uncontrolled pH favored the proliferation of microorganisms in harsh environment (e.g., Chitinophagaceae sp. and Sphingobacteriales sp.). Moreover, operational pH regulation enhanced the expression of critical genes involved in sulfur metabolism (e.g., SELENBP1 and SoxA), accompanied with glycolysis (e.g., ppgK and pfkB) and pyruvate metabolism (e.g., ackA and aceE), which could provide sufficient energy and electron. Conversely, these gene expressions were down-regulated in pH unregulation reactor, while the microbial adaptation mechanism was activated through the enhancement of DNA replication, quorum sensing, and two-component system, enabling resistance to extreme acidic conditions. This study would provide the in-depth understanding of operational pH regulation on organic sulfur degradation and transformation in MABR system and offer novel guidance for organic sulfur removal.

Osmotic response in Leptospirillum ferriphilum isolated from an industrial copper bioleaching environment to sulfate

Iron and sulfur-oxidizing microorganisms play important roles in several natural and industrial processes. Leptospirillum (L.) ferriphilum, is an iron-oxidizing microorganism with a remarkable adaptability to thrive in extreme acidic environments, including heap bioleaching processes, acid mine drainage (AMD) and natural acidic water. A strain of L. ferriphilum (IESL25) was isolated from an industrial bioleaching process in northern Chile. This strain was challenged to grow at increasing concentrations of sulfate in order to assess changes in protein expression profiles, cells shape and to determine potential compatible solute molecules. The results unveiled changes in three proteins: succinyl CoA (SCoA) synthetase, isocitrate dehydrogenase (IDH) and aspartate semialdehyde dehydrogenase (ASD); which were notably overexpressed when the strain grew at elevated concentrations of sulfate. ASD plays a pivotal role in the synthesis of the compatible solute ectoine, which was identified along with hydroxyectoine by using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF). The relationship between IDH, SCoA, and ectoine production could be due to the TCA cycle, in which both enzymes produce metabolites that can be utilized as precursors or intermediates in the biosynthesis of ectoine. In addition, distinct filamentous cellular morphology in L. ferriphilum IESL25 was observed when growing under sulfate stress conditions. This study highlights a new insight into the possible cellular responses of L. ferriphilum under the presence of high sulfate levels, commonly found in bioleaching of sulfide minerals or AMD environments.

Two-Step Bio-Dissolution of Metals from Printed Circuit Boards Using Acidophilic Iron- and Sulfur-Oxidizing Mesophiles

To date, electronic waste (e-waste) is the fastest-growing waste stream worldwide due to technological advancement and the advent of the Fourth Industrial Revolution. Although e-waste is an environmental hazard, these materials are considered good secondary sources of metals. This study examined the bioleaching of metals from printed circuit boards, where a two-step bioleaching approach was used with iron–sulfur-oxidizing microorganisms at different e-waste particle sizes. The metal analysis from the different particle sizes (PSs) showed that copper (Cu), tin (Sn), and lead (Pb) were predominantly deposited in the coarser fraction, ranging from 500 to 710 µm at 28.7, 20.5, and 11.1 wt.%, respectively. On the other hand, metals such as iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), and aluminum (Al) were mostly deposited in the finer fraction, which ranged from 38 to 150 µm at 37.3, 5.9, 8.8, 1.3, and 4.2 wt.%, respectively. After the bioleaching process, it was observed that higher metal extraction occurred at a PS ranging from 38 to 150 µm, which achieved recovery efficiency rates of 62.9%, 68.2%, 95.3%, 86.1%, 61.9%, 47.2%, 21.2%, and 63.6% for Al, Cu, Fe, Mn, Ni, Pb, Sn, and Zn, respectively, over 10 days.

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.

Review of Parameters, Performance Models, And Applications of Biofiltration Technology In Reducing H2S Compounds In The Air

High-quality air is essential for human survival. The present-day has a negative effect on air quality. Air contamination from the harmful compound H2S is an important problem. The primary source of H2S discharges is the oil and gas industry, where it is a by-product of resource harvesting and processing. Further sources of H2S discharges into the atmosphere include mining, waste management, and fossil fuel burning. H2S generates a malodorous scent resembling that of decayed eggs, which can prompt respiratory discomfort and irritation in humans and animals. At elevated concentrations, it may induce toxicity and even fatalities. Biofiltration is one of the latest remarkable technological advances for mitigating this issue. This method employs microorganisms to convert H2S into less harmful compounds. Biofiltration offers the major benefit of low operational expenditure and minimal environmental impact. This paper contributes to our comprehension of the microbial parameters, designs, models, applications and processes that affect biofilter efficiency. Diffusion-based biofiltration models show greater efficacy in design systems. Furthermore, advances in media, including the use of hollow cylindrical particles, have increased the efficiency of biofiltration. Sulfur-oxidizing microorganisms, such as Thiobacillus sp., play a pivotal role in decreasing H2S compounds. It is crucial to regularly monitor and regulate moisture levels, pH, temperature, and nutrient content to secure optimal and consistent biofiltration performance. The technology's effectiveness and stability heavily depend on precise control of these parameters. Biofiltration technology is hailed as a promising approach to manage H2S compounds, safeguard air quality, and preserve human health and the environment.

Effect of mechanical activation on biooxidation and gold extraction of a high-grade flotation concentrate using mesophilic and moderately thermophilic microorganisms

The effect of mechanical activation and biooxidation on the gold extraction from a high-grade (168 g/t) gold sulfide concentrate was investigated using a mixed culture of iron- and sulfur-oxidizing microorganisms. The influence of mechanical activation pretreatment, the nutrient medium type (Norris and 9K), initial pH, and microbial culture type was investigated on the biooxidation ability of mixed cultures of mesophilic and moderately thermophilic microorganisms. Results showed that gold extraction from the non-activated non-biooxidized concentrate was 83.9%, while after biooxidation, it reached 98.8%. The gold recovery from the mechanically activated non-biooxidized concentrate was 77.3%, which reached 97.6% after biooxidation. Therefore, biooxidation was found to have a significant positive effect on gold extraction, but mechanical activation had a negative effect on it in both abiotic and biotic media. The characterization of solid residues was performed by SEM/EDS and chemical analyses. Jarosite and gypsum were the main precipitates formed during biooxidation, especially in 9K nutrient medium. It was found that mechanical activation reduced the efficiency of biooxidation process mainly as a result of overcoming negative effects such as weak bacteria-mineral attachment, the release of toxic species, increasing pulp viscosity, and the coating of gold grains by less soluble solids on the positive effects such as the enhancing of surface area and the disordering of the crystal structure of refractory sulfide phases.

An isolated chemolithoautotrophic ecosystem deduced from environmental isotopes: Ayyalon cave (Israel)

The stable isotopes composition of chemolithoautotrophic cave ecosystems is known to differ from epigenic caves. Here we show that in addition, dead carbon (devoid of 14C), is utilized and transferred throughout this ecosystem, rendering it unsuitable for radiocarbon dating. The connectivity of the Ayyalon Cave ecosystem with the surface is studied, along with its sources of energy and carbon, as well as the interconnections between its constituents. We use isotopic evidence to show that its ancient resilient ecosystem is based on an underground food web depending on rich biomass production by chemolithoautotrophic nutrient supplies, detached from surface photosynthesis. Carbon isotopic values indicate that: (1) the microbial biota use bicarbonate from the groundwater (23.34 pMC [% of modern carbon]) rather than the atmospheric CO2 above the water (71.36 pMC); (2) the depleted 14C signal is transferred through the entire ecosystem, indicating that the ecosystem is well-adapted and based on the cave biofilm which is in turn based on groundwater-dissolved inorganic carbon. Incubation of Ayyalon biofilm with 14C-labelled bicarbonate indicates uptake of the radio-labeled bicarbonate by sulfur-oxidizing proteobacteria Beggiatoa, suggesting that these sulfur-oxidizing microorganisms use the water-dissolved inorganic carbon for chemolithoautotrophic carbon fixation. Organic matter in the cave is much lighter in its stable nitrogen and carbon isotopes compared with respective surface values, as expected in chemolithoautotrophic systems. This evidence may be applicative to subsurface voids of ancient Earth environments and extraterrestrial systems.

Bioprospecting for and the applications of halophilic acidophiles in bioleaching operations

The economic recovery of metals from sulfide ores has become a topic of increasing interest due to the escalating demand for critical minerals and the reducing grade of available ores. Bioleaching is the use of acidophilic iron and sulfur-oxidising microorganisms to facilitate the extraction of base metals from primary sulfide ores and tailings. One significant issue limiting the use of bioleaching is the availability of freshwater due to the sensitivity of these microbes to chloride. The use of saline tolerant acidophilic iron- and-sulfur oxidising microorganisms will go a long way to addressing this issue. There are three possible means of sourcing suitable microorganisms; adaptation, genetic engineering and bioprospecting, with bioprospecting showing the greatest possibilities. Bioprospecting in search of native organisms for bioleaching operations has led researchers to numerous locations around the world and the isolation of iron- and sulfur-oxidising acidophiles that are capable of tolerating high levels of salinity has been of particular interest in these investigations.

Sulfuric acid bioproduction and its application in rare earth extraction from phosphogypsum

Industrial production of sulfuric acid requires a high amount of energy and in remote regions such as mineral extraction pits, in situ production becomes unfeasible. This work proposes an alternative for the production of H2SO4 that uses sulfur-oxidizing microorganisms. The production capacity of this acid in a mesophilic (30 °C) and a thermophilic (65 °C) condition was studied by three collected consortia from acid mine drainage and compared with Acidithiobacillus thiooxidans. It was found that At. thiooxidans presented higher sulfuric acid production than the consortia collected and, therefore, it was selected for the bioleaching of rare earths elements (REEs) from phosphogypsum (PG). Due to the acid consumption of phosphogypsum, the two-step bioleaching condition resulted in higher REEs extraction (98% Nd, 60% Ce, 58% La, and 62% Y) when compared to one-step bioleaching (28% Nd, 17% Ce, 18% La, and 30% Y). The process was performed on a reactor scale and it was possible to extract 55.0% of the REEs contained in 300 g of waste and concentrate them into 0.922 g of rare earth oxalates, with a final yield of 52.5%, showing that the proposed bioprocess has potential application even in remote areas due to its low energy consumption when compared to traditional processes.

Biofilm Formation Is Crucial for Efficient Copper Bioleaching From Bornite Under Mesophilic Conditions: Unveiling the Lifestyle and Catalytic Role of Sulfur-Oxidizing Bacteria.

Biofilm formation within the process of bioleaching of copper sulfides is a relevant aspect of iron- and sulfur-oxidizing acidophilic microorganisms as it represents their lifestyle in the actual heap/dump mining industry. Here, we used biofilm flow cell chambers to establish laminar regimes and compare them with turbulent conditions to evaluate biofilm formation and mineralogic dynamics through QEMSCAN and SEM-EDS during bioleaching of primary copper sulfide minerals at 30°C. We found that laminar regimes triggered the buildup of biofilm using Leptospirillum spp. and Acidithiobacillus thiooxidans (inoculation ratio 3:1) at a cell concentration of 106 cells/g mineral on bornite (Cu5FeS4) but not for chalcopyrite (CuFeS2). Conversely, biofilm did not occur on any of the tested minerals under turbulent conditions. Inoculating the bacterial community with ferric iron (Fe3+) under shaking conditions resulted in rapid copper recovery from bornite, leaching 40% of the Cu content after 10 days of cultivation. The addition of ferrous iron (Fe2+) instead promoted Cu recovery of 30% at day 48, clearly delaying the leaching process. More efficiently, the biofilm-forming laminar regime almost doubled the leached copper amount (54%) after 32 days. In-depth inspection of the microbiologic dynamics showed that bacteria developing biofilm on the surface of bornite corresponded mainly to At. Thiooxidans, while Leptospirillum spp. were detected in planktonic form, highlighting the role of biofilm buildup as a means for the bioleaching of primary sulfides. We finally propose a mechanism for bornite bioleaching during biofilm formation where sulfur regeneration to sulfuric acid by the sulfur-oxidizing microorganisms is crucial to prevent iron precipitation for efficient copper recovery.

Mimicking the microbial oxidation of elemental sulfur with a biphasic electrochemical cell

The lack of an artificial system that mimics elemental sulfur (S8) oxidation by microorganisms inhibits a deep mechanistic understanding of the sulfur cycle in the biosphere and the metabolism of sulfur-oxidising microorganisms. In this article, we present a biphasic system that mimics biochemical sulfur oxidation under ambient conditions using a liquid|liquid (L|L) electrochemical cell and gold nanoparticles (AuNPs) as an interfacial catalyst. The interface between two solvents of very different polarity is an ideal environment to oxidise S8, overcoming the incompatible solubilities of the hydrophobic reactants (O2 and S8) and hydrophilic products (H+, SO32–, SO42–, etc.). Furthermore, the interfacial AuNPs provide a catalytic surface onto which O2 and S8 can adsorb. Control over the driving force for the reaction is provided by polarising the L|L interface externally and tuning the Fermi level of the interfacial AuNPs by the adsorption of aqueous anions. Comparison of electrochemical measurements using a 4-electrode closed bipolar electrochemical cell and a L|L electrochemical cell confirmed that electron transfer reactions are possible between O2, gold and S8 in biphasic systems.

Acidophilic chemolithotrophic microorganisms: prospects for use in biohydrometallurgy and microbial fuel cells

Acidophilic chemolithotrophic microorganisms are used in biohydrometallurgy for the extraction of metals from sulphide ores. Some types of microorganisms belonging to this group are capable of generating electricity under certain conditions. This circumstance determined a recent upsurge of research interest in their use in biofuel cells. Under a constant supply of the substrate to the bioelectrochemical system, acidophilic chemolithotrophic microorganisms are capable of producing electricity for a prolonged period of time. The use of extremophiles in microbial fuel cells is of particular interest, since these microorganisms can serve as bioelectrocatalysts at extreme pH, salinity and temperature, while the vast majority of microorganisms are unable to survive under these conditions. Therefore, selection of optimal conditions and approaches to controlling the work of acidophilic chemolithotrophic microorganisms in such fuel cells is of particular importance. On this basis, a technology for the simulteneous bioleaching of metals from poor ores and the generation of electricity can be developed. Biofuel cells operating at low pH values using acidophilic chemolithotrophic microorganisms are yet to be investigated. The number of studies on acidophilic electroactive microorganisms is very limited. In this regard, the purpose of this review was to consider the prospects for the use of acidophilic chemolithotrophic microorganisms as bioagents in microbial fuel cells. The reviewed publications demonstrate that chemolithotrophic microorganisms can act as both anodic (metal-reducing, sulphur-oxidizing microorganisms) and cathodic (metal-oxidizing prokaryotes, sulfate reducers) highly efficient bioagents capable of using mining wastes as substrates.

Toward Sustainable Solution for Biooxidation of Waste and Refractory Materials Using Neutrophilic and Alkaliphilic Microorganisms-A Review.

The significant increase in economic concern and environmental restrictions has resulted in increasing interest in biotechnological solutions. The application of acidophilic, sulfur-oxidizing microorganisms in biomining and in the treatment of waste matrices has been extensively explored. However, to surmount the current challenges encountered by the industrial use of acidophiles, there is an opportunity for neutrophilic and alkaliphilic microorganisms to be comprehensively considered for the biooxidation of refractory sulfide materials. This review, for the first time, provides a detailed study of neutrophiles and alkaliphiles that have potential for oxidizing sulfur-containing wastes and sulfide refractory ores to recover entrapped metals especially gold in a sustainable manner. The study illustrates the applicability of neutrophilic and alkaliphilic microorganisms to provide better and sustainable alternatives for the recovery of metals from wastes from various sources as well as refractory materials. The microorganisms summarized in this review have been successfully used in oxidizing different sulfide sources by achieving high oxidizing efficiencies (>80%) in numerous technologies. The fundamentals of biooxidation along with possible mechanisms involved in the biooxidation have been discussed in detail.

Carbonaceous matter degradation by fungal enzyme treatment to improve Ag recovery from an Au-Ag-bearing concentrate

Sequential treatment was applied to carbonaceous Au-Ag-bearing ore concentrate to maximize the Au and Ag recovery. In the preliminary test, the present carbonaceous ore had well liberated and exposed type of gold grains, which are not refractory, but included mainly three types of Ag presented as electrum, hessite (Ag2Te) and Ag-bearing other minerals. Au recovery was ∼100% without any treatment, meanwhile Ag recovery was only 33.3%. The sequential treatment comprises two oxidation steps: (a) mixed culture of iron- and sulfur-oxidizing microorganisms at pH 1.2, followed by (b) cell-free spent medium (CFSM) at pH 4.0 from a white rot-fungus, Phanerochaete chrysosporium, which includes lignin-degrading enzymes. As a result, Ag recovery was 55.5% after the first step and greatly improved to ∼100%, including the dissolved Ag+ concentration in the first step of acid treatment. Although the acidophilic iron-oxidizing microorganisms were inhibited by dissolved Ag+ and Cd2+ ions, the strong acidic conditions dissolved hessite and Ag-bearing oxide minerals. However, the remaining carbonaceous matter acted to sorb Ag(CN)2− in cyanidation, causing the recovery loss. In the next step the lignin-degrading enzymes degraded carbonaceous matter in the ore. This step is necessary to avoid the adsorption of Ag(CN)2− on graphitic carbonaceous matter, leading a mostly perfect recovery of the remaining Ag in the solid residues, without necessity of alkaline washing. The sequential treatment including enzymatic lignin-degrading process was also effective in carbonaceous silver ore avoiding the emission of air pollutants.

Identification of cable bacteria and its biogeochemical impact on sulfur in freshwater sediments from the Wenyu River

Cable bacteria are filamentous sulfur-oxidizing microorganisms that couple the reduction of oxygen or nitrate in surface sediments with the oxidation of free sulfide in deeper sediments by transferring electrons across centimeter scale distances. The distribution and activities of cable bacteria in freshwater sediments are still poorly understood, especially the impact of cable bacteria on sulfur cycling. The goal of this study was to investigate electrogenic sulfide oxidation associated with cable bacteria in laboratory microcosm incubations of freshwater sediments using microsensor technology, 16S full-length rRNA sequencing, and fluorescence in situ hybridization (FISH) microscopy. Their activity was characterized by a pH maximum of 8.56 in the oxic zone and the formation of a 13.7 ± 0.6 mm wide suboxic zone after 25 days of incubation. Full-length 16S rRNA gene sequences related to cable bacteria were recovered from the sediments and exhibited 93.3%–99.4% nucleotide (nt) similarities with those from other reported freshwater cable bacteria, indicating that new species of cable bacteria were present in the sediments. FISH analysis indicated that cable bacteria density increased with time, reaching a maximum of 95.48 m cm−2 on day 50. The cells grew downwards to 40 mm but were mainly concentrated on the top 0–20 mm of sediment. The cable bacteria continuously consumed H2S in deeper layers and oxidized sulfide into sulfate in the 0–20 mm surface layers, thereby affecting the sulfur cycling within sediments. These findings provide new evidence for the existence of higher diversity of cable bacteria in freshwater sediments than previously known.

Simultaneous removal of iron and sulfate from biodesulfurization solutions of a coking coal by jarosite precipitation

Precipitation of iron- and sulfate-bearing prohibitive layers on the surface of coal particles during heap biodesulfurization is a problematic issue due to the decreasing of biodepyritization rate, causing permeability problems in bioheaps, and reducing the caking properties of coking coals. In this regard, the biodesulfurization of Parvadeh high-pyrite coking coal (Tabas, Iran) was conducted using a mixed culture of iron-and sulfur-oxidizing microorganisms and the ferric level of the bioleaching solution was controlled by jarosite precipitation. The main and interaction effects of some critical parameters including temperature, retention time, the molar ratio of ammonia to iron (MR Ammonia: Iron) and seed addition on the removal of iron from the biodesulfurization solution was investigated by jarosite precipitation using a response surface methodology (RSM). The results were evaluated by the analysis of variance (ANOVA). It was found that 98.4 % iron removal and 62.1 % sulfate removal was achieved at the temperature of 95 °C, the retention time of 2.5 h, the MRAmmonia:Iron of 0.8 and seed addition of 40 g/L. Temperature had the most effect of iron removal efficiency. The precipitates were analyzed by SEM/EDS and XRD analyses. A developed flowsheet was proposed to treat the biodesulfurization solution of coals in bioheaps.

Geomicrobiology of Mine Tailings from Malanjkhand Copper Project, India

Geomicrobiology of mine tailing from Asia’s largest open-cast Cu mine at Malanjkhand was established, emphasizing the roles of microorganisms in acidification process using 16S rRNA gene amplicon and shotgun metagenomics. Mine tailings collected from five different locations portrayed the characteristic oligotrophic geochemical nature, with varying pH (pH 1.9–7.2), high heavy metals (Fe, Cu, Zn, Ni) and sulfate, but reduced, carbon, nitrogen and phosphate content. Iron-oxides and sulfate mineral phases were detected. Highly acidophilic, iron- and sulfur-oxidizing microorganisms including Sulfobacillus, Acidithiobacillus, Leptospirillium, Ferrimicrobium, Ferrithrix, etc. encoding the genes necessary for chemolithoautotrophic metabolism (sqr, sox, cbbL, cox, cyc1, etc.), resistance to low pH (sqh, kdp, gadB, etc.) and heavy metal stress (cop, cus, czc, chr, etc.) predominated the oxidized tailings. A markedly different microbial community represented by Thiobacillus, Sphingomonas, Meiothermus, Sulfurifustis, and members of Hydrogenophilaceae, Acidiferrobacteraceae, Gaiellales, Gemmatimonadetes, Ignavibacteriales, KD4-96, etc. predominated the fresh tailings. Metagenome of the fresh tailings confirmed presence of similar sets of genes as found in oxidized tailings, however, taxonomic affiliations of most of these functional genes vary between the two habitats, indicating differential taxa recruitment under the two contrasting ecological conditions. The study provided an in-depth understanding of Cu mine tailings microbial community and their role in acidification process.