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Climate change is rapidly transforming Arctic landscapes where increasing soil temperatures speed up permafrost thaw. This exposes large carbon stocks to microbial decomposition, possibly worsening climate change by releasing more greenhouse gases. Understanding how microbes break down soil carbon, especially under the anaerobic conditions of thawing permafrost, is important to determine future changes. Here, we studied the microbial community dynamics and soil carbon decomposition potential in permafrost and active layer soils under anaerobic laboratory conditions that simulated an Arctic summer thaw. The microbial and viral compositions in the samples were analyzed based on metagenomes, metagenome-assembled genomes, and metagenomic viral contigs (mVCs). Following the thawing of permafrost, there was a notable shift in microbial community structure, with fermentative Firmicutes and Bacteroidota taking over from Actinobacteria and Proteobacteria over the 60-day incubation period. The increase in iron and sulfate-reducing microbes had a significant role in limiting methane production from thawed permafrost, underscoring the competition within microbial communities. We explored the growth strategies of microbial communities and found that slow growth was the major strategy in both the active layer and permafrost. Our findings challenge the assumption that fast-growing microbes mainly respond to environmental changes like permafrost thaw. Instead, they indicate a common strategy of slow growth among microbial communities, likely due to the thermodynamic constraints of soil substrates and electron acceptors, and the need for microbes to adjust to post-thaw conditions. The mVCs harbored a wide range of auxiliary metabolic genes that may support cell protection from ice formation in virus-infected cells.ImportanceAs the Arctic warms, thawing permafrost unlocks carbon, potentially accelerating climate change by releasing greenhouse gases. Our research delves into the underlying biogeochemical processes likely mediated by the soil microbial community in response to the wet and anaerobic conditions, akin to an Arctic summer thaw. We observed a significant shift in the microbial community post-thaw, with fermentative bacteria like Firmicutes and Bacteroidota taking over and switching to different fermentation pathways. The dominance of iron and sulfate-reducing bacteria likely constrained methane production in the thawing permafrost. Slow-growing microbes outweighed fast-growing ones, even after thaw, upending the expectation that rapid microbial responses to dominate after permafrost thaws. This research highlights the nuanced and complex interactions within Arctic soil microbial communities and underscores the challenges in predicting microbial response to environmental change.

Rates of microbial processes are fundamental to understanding the significance of microbial impacts on environmental chemical cycling. However, it is often difficult to quantify rates or to link processes to specific taxa or individual cells, especially in environments where there are few cultured representatives with known physiology. Here, we describe the use of the redox-enzyme-sensitive molecular probe RedoxSensor™ Green to measure rates of anaerobic electron transfer physiology (i.e., sulfate reduction and methanogenesis) in individual cells and link those measurements to genomic sequencing of the same single cells. We used this method to investigate microbial activity in hot, anoxic, low-biomass (~103 cells mL-1) groundwater of the Death Valley Regional Flow System, California. Combining this method with electron donor amendment experiments and metatranscriptomics confirmed that the abundant spore formers including Candidatus Desulforudis audaxviator were actively reducing sulfate in this environment, most likely with acetate and hydrogen as electron donors. Using this approach, we measured environmental sulfate reduction rates at 0.14 to 26.9 fmol cell-1 h-1. Scaled to volume, this equates to a bulk environmental rate of ~103 pmol sulfate L-1 d-1, similar to potential rates determined with radiotracer methods. Despite methane in the system, there was no evidence for active microbial methanogenesis at the time of sampling. Overall, this method is a powerful tool for estimating species-resolved, single-cell rates of anaerobic metabolism in low-biomass environments while simultaneously linking genomes to phenomes at the single-cell level. We reveal active elemental cycling conducted by several species, with a large portion attributable to Ca. Desulforudis audaxviator.

High concentrations of harmful metal(loid)s and extreme acidity are persistent environmental concerns in acidic pit lakes. In this study, we examine Cueva de la Mora (CM), a meromictic pit lake in the Iberian Pyrite Belt, Spain, as a model system. Our research aims to explore potential bioremediation strategies to mitigate the impacts of metal(loid)s and acidity in such environments. The major strategy applied in this research is to biologically stimulate sulfate reduction (i.e., biosulfidogenesis) in the deep layer of the lake to promote the formation of low-solubility sulfide minerals. Previous omics-based studies of CM have shown that several sulfate-reducing bacteria (SRB) taxa are present in the deep layer. However, their activities are likely limited by the availability of electron donors for sulfide production. Therefore, different amendments (glycerol, elemental sulfur, and glycerol + elemental sulfur) were tested to promote sulfide production and enrich acid-tolerant sulfide-producing microbes. Our results showed that glycerol stimulated dissimilatory sulfate reduction much faster than elemental sulfur alone, suggesting that electron donor limitations control sulfide production. Furthermore, the combined addition of glycerol and elemental sulfur (S(0)) resulted in the highest level of sulfide production. This indicates that S(0) can play a significant role as an electron acceptor in further promoting sulfide production when a suitable electron donor is present. Microbial community analysis revealed that Desulfosporosinus acididurans , a previously discovered acid-tolerant SRB, was enriched and became the dominant species in incubations with glycerol only (~76–96% abundance) or the combination of glycerol and S(0) (~93–99% abundance). [ABSTRACT FROM AUTHOR]

Increasing plastic pollution is a serious environmental problem as widespread production and inadequate disposal of plastic materials lead to adverse impacts on ecosystems. The structural and functional characteristics of the anaerobic microbial community contacting with extruded polystyrene (XPS) waste were investigated under methanogenic (MG) and nitrate-(NR) and sulfate-reducing (SR) conditions. The presence of XPS in the microbial community was shown to have no negative effect on the processes of biogas formation and, on the contrary, resulted in an increase in the yield of methane and volatile fatty acids and a change in their ratio. Microparticles of different sizes were found in the culture liquid of the variants with XPS: 2.4 × 106/mL (NR), 1.2 × 106/mL (SR), and 0.4 × 106/mL (MG), while no microparticles were found in the control variants. Scanning electron microscopy revealed that in all experimental variants the surface of the polymer became looser, more textured, with formation of irregularities, cracks, and holes. Increased diversity in the microbial community associated with an increase in the number of microbial morphotypes, correlated with the results of high-throughput sequencing of the 16S rRNA gene. When XPS was introduced into an anaerobic community incubated in different donor-acceptor conditions, the number of microbial groups in it increased, as well as the proportion of hydrolytic and acidogenic bacteria (Sedimentibacter, Lentimicrobium), acetogenic syntrophs (Syntrophomonas, Desulfovibrio, Geobacter), and methanogenic archaea (Methanosarcina, Methanobacterium). Our study showed that the XPS waste was not inert for the microbial community, the contact with it resulting in significant changes in its structure and functioning. Changes in the sample surface, emergence of microparticles, and differences in the composition of the intermediate and terminal metabolic products may indicate slow partial degradation of the plastic via fragmentation. However, since the experiments were carried out using household XPS containing various fillers apart from the main polymer, it is probable that, along with polystyrene, additional substances included in its composition (plasticizers, dyes, etc.) are also subject to degradation. The ability of microorganisms to degrade the polymer itself requires further research. [ABSTRACT FROM AUTHOR]

Stibnite precipitates in the form of massive boulders at two active hydrothermal mounds in the submarine Wakamiko Crater (Ryukyu Volcanic Arc) as opposed to commonly observed accessory stibnite in the seafloor hydrothermal deposits. The stibnite dimorph, metastibnite, found here for the first time on the seafloor, appears to always form whenever stibnite is precipitated under submarine hydrothermal conditions. Our study shows that hydrothermal conditions of low temperatures (<50 °C) and low values of pH (<6) are favorable for the precipitation of stibnite on the seafloor. The stibnite probably does not precipitate at the measured vent fluid temperatures (i.e., 177.6–187.0 °C) along the chimney conduits, but rather at temperatures <50 °C and at slightly reduced to slightly oxic conditions (Eh = –0.5 to +0.5 V) within the chimney walls and hydrothermal mounds. Metastibnite deposition appears to be the result of rapid quenching of hot hydrothermal fluid when mixed with cold seawater and rapid precipitation at the interface between stibnite and vent fluid. The low concentrations (usually below detection limits) of the trace elements (Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, P, Pb, Sr, V, Zn) in the stibnite deposits from Wakamiko Crater are likely a result of the decreased metal-transporting capacity of the precipitating vent fluid due to its low chlorinity. Low-chlorinity venting implies sub-seafloor boiling and phase separation of the hydrothermal fluid. Sluggish hydrothermal fluid/seawater mixing within the walls of the chimneys and mounds favors the reduction of sulfate dissolved in the hydrothermal fluids and results in a heavy S isotope composition of the sulfate in the vent fluids. Sulfate reduction and disproportionation of magmatic SO2, both leading to heavy S isotope composition of sulfate in the vent fluids, seem to be common processes in volcanic arc/back-arc submarine hydrothermal settings. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur. [ABSTRACT FROM AUTHOR]

There is an increasing demand for cost-effective semi-passive water treatment that can withstand challenging climatic conditions and effectively and sustainably manage mine-impacted water in (sub)arctic regions. This study investigated the ability of four pilot-scale bioreactors inoculated with locally sourced bacteria and affected by a freeze–thaw cycle to remove selenium and antimony. The bioreactors were operated at a Canadian (sub)arctic mine for a year. Two duplicate bioreactors were installed in a heated shed that was maintained at 5 °C over the winter, while two other duplicates were installed outdoors and left to freeze. The removal rate of selenium and antimony was monitored weekly, while a genomic characterization of the microbial populations in the bioreactors was performed monthly. The overall percentage of selenium and antimony removal was similar in the outside (10–93% Se, 20–96% Sb) and inside (35–94% Se, 10–95% Sb) bioreactors, apart from the spring thawing period when removal in the outdoor bioreactors was slightly lower for Se. The dominant taxonomic groups of microbial populations in all bioreactors were Bacteroidota, Firmicutes, Desulfobacterota and Proteobacteria. The microbial population composition was consistent and re-established quickly after spring thaw in the outside bioreactors. This demonstrated that the removal capacity of bioreactors inoculated with locally sourced bacteria was mostly unaffected by a freeze–thaw cycle, highlighting the strength of using local resources to design bioreactors in extreme climatic conditions. [ABSTRACT FROM AUTHOR]

Bedded barite, Fe-Zn-Pb sulfides, carbonates, and cherts within Ediacaran (Dalradian Supergroup) graphitic metasediments near Aberfeldy in Scotland have previously been interpreted as chemical sediments precipitated from hydrothermal fluids episodically exhaled into marine basins filled with organic-rich mud, silt, and sand. Lithological variation and compositional diversity in pyrite and sphalerite reflect varied redox environments and proximity to hydrothermal discharges. Thick beds (>2 m) of barite have relatively uniform δ34S of +36 ± 1.5‰, considered to represent contemporaneous seawater sulfate, as negative Δ17O indicates incorporation of atmospheric oxygen during precipitation in the water column. However, certain features suggest that diagenetic processes involving microbial sulfate reduction modified the mineralogy and isotopic composition of the mineralization. Barite bed margins show decimeter-scale variation in δ34S (+32 to +41‰) and δ18O (+8 to +21‰), attributed to fluid-mediated transfer of dissolved barium and sulfate between originally porous barite and adjacent sediments, in which millimetric sulfate crystals grew across sedimentary lamination. Encapsulated micron-sized barium carbonates indicate early diagenetic barite dissolution with incorporation of sulfur into pyrite, elevating pyrite δ34S. Subsequently, sulfidation reactions produced volumetrically minor secondary barite with δ34S of +16 to +22‰. Overall, these processes affected small volumes of the mineralization, which originally formed on the seafloor as a classic SEDEX deposit. [ABSTRACT FROM AUTHOR]

[Display omitted] • Increased temperature stimulates the production of H 2 S. • Sulfate reduction under temperature decrease influenced by electron donor species. • Continuous input of organic matter and SO 4 2- induce landfill odor risk. In the leachate-saturation zone of landfills, sulfate reduction is influenced by temperature and electron donors. This study assessed sulfate reduction behaviors under varied electron donor conditions by establishing multiple temperature variation scenarios based on stable temperature fields within the leachate-saturation zone. The results showed that temperature variations altered the microbial community structure and significantly influenced the sulfate reduction process. A more pronounced effect was observed with a temperature difference of 30 °C compared to one of 10 °C. In addition, sulfate reduction was influenced by the presence of electron donors and acceptors. In the middle and low-temperature regions (35 °C and 25 °C), sulfate reduction reaction of acidic organic matter was more significant, while alcohol and saccharide organic substances were more effective in promoting sulfate reduction at high-temperature regions (55 °C). Notably, a 30 °C temperature difference within the leachate-saturation zone significantly altered the microbial community structure, which influenced the sulfate reduction behavior. In particular, Firmicutes and Synergistota played essential roles in mediating the variance in sulfate reduction efficiency with a 30 °C decrease and 30 °C increase, respectively. The results also revealed that temperature changes within landfills were influenced by leachate migration, therefore, controlling leachate recharge can help prevent secondary risks associated with sulfate reduction processes. [ABSTRACT FROM AUTHOR]

We investigated the total sediment O2 uptake (TOU), sulfate reduction rate (SRR), and benthic nutrient flux (BNF) at the Yellow Sea cold water mass (YSCWM) sediments (N3509 and N3507) and the coastal sediment (N3503) in the southern Yellow Sea. The organic carbon (OC) content increased from coarse- to fine-grained sediment, which was by far the highest at N3503 (0.89% and 6.1 Ø), followed by N3509 (0.72% and 4.5 Ø) and N3507 (0.15% and 3.0 Ø). The bottom water temperature at N3503 (16.0°C) was 6‒7°C higher than N3509 (10.2°C) and N3507 (9.0°C). The TOU and SRR at N3503 were 24.5 ± 5.0 mmol O2 m–2 d–1 and 6.5 mmol S m–2 d–1, 3‒6 times higher than the values measured at N3509 and N3507 (5.5 ± 0.2 and 4.2 ± 0.3 O2 mmol m–2 d–1 and 0.9 and 0.7 mmol S m–2 d–1, respectively). TOU showed a positive correlation with both the OC content and the bottom water temperature (R = 0.71, p < 0.001). The BNF at N3503 (3.4 mmol N m–2 d–1, 0.5 mmol P m–2 d–1, 3.8 mmol Si m–2 d–1) was 3‒37 times higher than the values measured at N3509. The BNF contributed 72–179% of the nutrients required for primary production at N3503, whereas the contribution was less than 30% at N3509. [ABSTRACT FROM AUTHOR]

The results of long-term studies of the conjugate distribution of methane (CH4) and sulfide sulfur (Ssulfide) concentrations in the bottom sediments of watercourses of the steppe zone of the European part of Russia are analyzed. In addition to CH4 and Ssulfide, Eh and pH values, humidity and density were determined in different sediment horizons; CH4, dry residue, and pH values were determined in water. Concentrations of CH4 in the watercourses vary from <0.1 to 2007.0 μL/L (median 24.3 μL/L), with the largest number of values (72%) in the range 10.1–100.0 μL/L. The concentrations of CH4 and Ssulfide in the bottom sediments of watercourses are quite high and vary, respectively, from <0.01 to 51.0 µg/g of wet sediment (median 1.35 µg/g) and from <0.001 to 4.50 mg/g of wet sediment (median 0.813 mg/g). Usually, the CH4 and Ssulfide concentrations increase from the surface layer to the subsurface horizons, and then decrease. The difference between the distributions of Ssulfide and CH4 is the more frequent occurrence of maximum concentrations of Ssulfide in less deep sediment horizons. Seasonal changes were recorded in the vertical distribution of CH4 and Ssulfide not only in terms of their concentrations, but also in the position of maximum and minimum values. There is a weak positive correlation between the concentrations of CH4 and Ssulfide, which indicates the synchronous formation of these gases in separate layers of sediments of the studied watercourses. The positive correlation established between the CH4 concentrations in water and 0–2 cm layer of bottom sediments indicates that the sediments are an important source of CH4 in water and its emission into the atmosphere. [ABSTRACT FROM AUTHOR]

BACKGROUND: Dyes present in textile wastewater can pose various environmental problems, including toxicity, carcinogenicity and mutagenicity, when released into receiving environments. Sulfidogenic bacteria play a crucial role in wastewater treatment by reducing sulfate and producing sulfide through the utilization of organic compounds in water. The resulting sulfide often transfers its electrons to another electron acceptor. This study focused on the treatment of real textile wastewater using an up‐flow sulfidogenic column bioreactor. RESULTS: The reactor was acclimated to sulfate‐reducing conditions when influent chemical oxygen demand and sulfate concentrations were 1742 and 2000 mg L−1, respectively. Subsequently, a gradual transition was made from sulfate‐reducing conditions to dye‐reducing conditions. Throughout the study, the hydraulic retention time was maintained at 1 day. CONCLUSION: The influent dye concentration was 2722 Pt‐Co, and an impressive dye removal efficiency of approximately 90 ± 2% was achieved. This corresponds to a removal rate of 2450 Pt‐Co L−1 day−1. Although the sulfide concentration in the reactor decreased in the last period, investigating the extent to which this sulfide participates in the dye removal may expand the use of sulfidogenic reactors in the treatment of real textile industry wastewater. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Groundwater contaminated by benzene and toluene is a common issue, posing a threat to the ecosystems and human health. The removal of benzene and toluene under sulfate-reducing condition is well known, but how the bacterial community shifts during this process remains unclear. This study aims to evaluate the shift in bacterial community structure during the biodegradation of benzene and toluene under sulfate-reducing condition. In this study, groundwater contaminated with benzene and toluene were collected from the field and used to construct three artificial samples: Control (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L, and HgCl2 250 mg/L), S1 (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L), and S2 (benzene 100 mg/L, toluene 2.5 mg/L, sulfate 940 mg/L). The contaminants (benzene and toluene), geochemical parameters (sulfate, ORP, and pH), and bacterial community structure in the artificial samples were monitored over time. By the end of this study (day 90), approximately 99% of benzene and 96% of toluene could be eliminated in both S1 and S2 artificial samples, while in the Control artificial sample the contaminant levels remained unchanged due to microbial inactivation. The richness of bacterial communities initially decreased but subsequently increased over time in both S1 and S2 artificial samples. Under sulfate-reducing condition, key players in benzene and toluene degradation were identified as Pseudomonas, Janthinobacterium, Novosphingobium, Staphylococcus, and Bradyrhizobium. The results could provide scientific basis for remediation and risk management strategies at the benzene and toluene contaminated sites. [ABSTRACT FROM AUTHOR]

IntroductionMolecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities.MethodsWe measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis.ResultsHydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H2) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41–0.52 nM H2) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312–2.56 nM H2) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08–2.18 nM H2). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB.DiscussionWe conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB’s more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

High concentrations of harmful metal(loid)s and extreme acidity are persistent environmental concerns in acidic pit lakes. In this study, we examine Cueva de la Mora (CM), a meromictic pit lake in the Iberian Pyrite Belt, Spain, as a model system. Our research aims to explore potential bioremediation strategies to mitigate the impacts of metal(loid)s and acidity in such environments. The major strategy applied in this research is to biologically stimulate sulfate reduction (i.e., biosulfidogenesis) in the deep layer of the lake to promote the formation of low-solubility sulfide minerals. Previous omics-based studies of CM have shown that several sulfate-reducing bacteria (SRB) taxa are present in the deep layer. However, their activities are likely limited by the availability of electron donors for sulfide production. Therefore, different amendments (glycerol, elemental sulfur, and glycerol + elemental sulfur) were tested to promote sulfide production and enrich acid-tolerant sulfide-producing microbes. Our results showed that glycerol stimulated dissimilatory sulfate reduction much faster than elemental sulfur alone, suggesting that electron donor limitations control sulfide production. Furthermore, the combined addition of glycerol and elemental sulfur (S(0)) resulted in the highest level of sulfide production. This indicates that S(0) can play a significant role as an electron acceptor in further promoting sulfide production when a suitable electron donor is present. Microbial community analysis revealed that Desulfosporosinus acididurans, a previously discovered acid-tolerant SRB, was enriched and became the dominant species in incubations with glycerol only (~76–96% abundance) or the combination of glycerol and S(0) (~93–99% abundance).

Theoretical issues of joint underground storage of hydrogen with methane are poorly studied, and practical examples are rare. Therefore, it is extremely important to analyze the mutual influence of hydrogen-methane mixtures and the host geological environment. This article presents material that makes it possible to substantiate the most significant hydrochemical processes that affect the transformation of cap rocks. For this purpose, the results of our own experiments, as well as published data on the study of the influence of hydrochemical conditions on the diffusion loss of hydrogen, its interaction with rock-forming minerals, organic matter, and pore waters were used. A quantitative assessment of the decrease in the moisture saturation of clay-rocks samples and, as a consequence, the loss of the mass content of mineral and organic substances is given. It was found that the cyclic change of thermobaric effects leads to a change in the redox conditions in the system “rock ↔ pore water” and is accompanied by an increase in the reactivity of calcium, magnesium, sulfur, iron. The saturation indices of pore water with carbonate and sulfate calcium salts were calculated under the conditions of their precipitation, dissolution, and removal from solution. The interpretation of the experimental data made it possible to substantiate the most probable transformations in clayey cap rocks, which affect their screening capabilities. It is recommended to take into account, when designing and operating storage facilities for hydrogen-methane mixtures, the variety of accompanying hydrochemical and microbiological processes that affect the change in the filtration properties of cap rocks.

Coal reservoirs are habitats for microorganisms, with some widespread communities linked to carbon cycling. The geographic distribution and metabolic expression of these microorganisms remain largely decoupled from the reservoir environment. Although microbial metabolism under natural conditions is insufficient for gas accumulation, the community influence from organic matter supply and environmental conditions can stimulate a positive response in the in-situ reservoir environment and coalbed methane storage. The southern Qinshui Basin is rich in coalbed methane resources and is one of the first areas in China to realize a commercial exploitation. Taking the Shizhuangnan block in the southern Qinshui Basin as an example, the geochemical characteristics of reservoir water and the biogeochemical sequencing of microbial genes are assessed by assessing ion concentrations, dissolved inorganic carbon isotopes, sulfate isotopes, and microbial abundance and diversity. The results show that the reservoir geochemistry is influenced by hydration, ion exchange, and microbial metabolism. High sodium and bicarbonate ion content indicate relatively reduced or stagnant conditions in the reservoir. Sulfate reducing bacteria and methanogens display synergy during coal degradation. However, sulfate reducing bacteria can outcompete methanogens for substrate when sulfate is sufficient for their metabolism, inhibiting methanogenesis. The sulfate isotopes, dissolved inorganic carbon isotopes, and microbial abundance and diversity may reflect the symbiotic relationship between these microorganisms and the reservoir environment. Regions with active sulfate reduction but weak methanogenesis generally do not provide suitable conditions for effective coalbed methane storage. Relatively reduced or stagnant reservoir environments favor methanogenesis and are beneficial for coalbed methane storage. This research enriches our methods for evaluating reservoir biogeochemistry, guides us in selecting favorable areas for coalbed methane exploration and development, and provides a theoretical basis and guidance for the practical implementation of coalbed methane bioengineering.

Some Alphaproteobacteria contain intracytoplasmic membranes (ICMs) and proteins homologous to those responsible for the mitochondrial cristae, an observation which has given rise to the hypothesis that the Alphaproteobacteria endosymbiont had already evolved cristae-like structures and functions. However, our knowledge of microbial fine structure is still limited, leaving open the possibility of structurally homologous ICMs outside the Alphaproteobacteria. Here, we report on the detailed characterization of lamellar cristae-like ICMs in environmental sulfate-reducing Desulfobacterota that form syntrophic partnerships with anaerobic methane-oxidizing (ANME) archaea. These structures are junction-bound to the cytoplasmic membrane and resemble the form seen in the lamellar cristae of opisthokont mitochondria. Extending these observations, we also characterized similar structures in Desulfovibrio carbinolicus, a close relative of the magnetotactic D. magneticus, which does not contain magnetosomes. Despite a remarkable structural similarity, the key proteins involved in cristae formation have not yet been identified in Desulfobacterota, suggesting that an analogous, but not a homologous, protein organization system developed during the evolution of some members of Desulfobacterota. IMPORTANCE Working with anaerobic consortia of methane oxidizing ANME archaea and their sulfate-reducing bacterial partners recovered from deep sea sediments and with the related sulfate-reducing bacterial isolate D. carbinolicus, we discovered that their intracytoplasmic membranes (ICMs) appear remarkably similar to lamellar cristae. Three-dimensional electron microscopy allowed for the novel analysis of the nanoscale attachment of ICMs to the cytoplasmic membrane, and these ICMs are structurally nearly identical to the crista junction architecture seen in metazoan mitochondria. However, the core junction-forming proteins must be different. The outer membrane vesicles were observed to bud from syntrophic Desulfobacterota, and darkly stained granules were prominent in both Desulfobacterota and D. carbinolicus. These findings expand the taxonomic breadth of ICM-producing microorganisms and add to our understanding of three-dimensional microbial fine structure in environmental microorganisms.

The activity of subsurface microorganisms can be harnessed for engineering projects. For instance, the Swiss radioactive waste repository design can take advantage of indigenous microorganisms to tackle the issue of a hydrogen gas (H2) phase pressure build-up. After repository closure, it is expected that anoxic steel corrosion of waste canisters will lead to an H2 accumulation. This occurrence should be avoided to preclude damage to the structural integrity of the host rock. In the Swiss design, the repository access galleries will be backfilled, and the choice of this material provides an opportunity to select conditions for the microbially-mediated removal of excess gas. Here, we investigate the microbial sinks for H2. Four reactors containing an 80/20 (w/w) mixture of quartz sand and Wyoming bentonite were supplied with natural sulfate-rich Opalinus Clay rock porewater and with pure H2 gas for up to 108 days. Within 14 days, a decrease in the sulfate concentration was observed, indicating the activity of the sulfate-reducing bacteria detected in the reactor, e.g., from Desulfocurvibacter genus. Additionally, starting at day 28, methane was detected in the gas phase, suggesting the activity of methanogens present in the solid phase, such as the Methanosarcina genus. This work evidences the development, under in-situ relevant conditions, of a backfill microbiome capable of consuming H2 and demonstrates its potential to contribute positively to the long-term safety of a radioactive waste repository. [ABSTRACT FROM AUTHOR]

The main sources of redox gradients supporting high-productivity life in the Europan and other icy ocean world oceans were proposed to be photolytically derived oxidants, such as reactive oxygen species (ROS) from the icy shell, and reductants (Fe(II), S(-II), CH4, H2) from bottom waters reacting with a (ultra)mafic seafloor. Important roadblocks to maintaining life, however, are that the degree of ocean mixing to combine redox species is unknown, and ROS damage biomolecules. Here, we envisage a unique solution using an acid mine drainage (AMD)-filled pit lakes analog system for the Europan ocean, which previous models predicted to be acidic. We hypothesize that surface-generated ROS oxidize dissolved Fe(II) resulting in Fe(III) (hydr)oxide precipitates, that settle to the seafloor as "iron snow." The iron snow provides a respiratory substrate for anaerobic microorganisms ("breathing iron"), and limits harmful ROS exposure since they are now neutralized at the ice-water interface. Based on this scenario, we calculated Gibbs energies and maximal biomass productivities of various anaerobic metabolisms for a range of pH, temperatures, and H2 fluxes. Productivity by iron reducers was greater for most environmental conditions considered, whereas sulfate reducers and methanogens were more favored at high pH. Participation of Fe in the metabolic redox processes is largely neglected in most models of Europan biogeochemistry. Our model overcomes important conceptual roadblocks to life in icy ocean worlds and broadens the potential metabolic diversity, thus increasing total primary productivity, the diversity and volume of habitable environmental niches and, ultimately, the probability of biosignature detection. [ABSTRACT FROM AUTHOR]

Depending on the season, the primary production of planktonic communities determined by radiotracer analysis varied within a broad range, from 6 to 314 µg C/(L h). Primary production in cyanobacterial mats was 4.2‒10.9 × 103 µg C/(dm3 h), and Chl a content varied from 6‒13 to 132‒140 mg Chl a/m2. For the plankton, the highest values were revealed in summer (25‒46 mg Chl a/m3), with the maximum in August (223 mg Chl a/m3). High abundance of bacterioplankton (0.3‒7.4 × 106 cells/mL) and massive growth of diatoms (0.15 × 106 cells/mL) with predominance of the genus Chaetoceros were found. Sulfate reduction rates varied from 0.037 µmol S/(dm3 h) in the upper reach to 61.87 µmol S/(dm3 h) in the river mouth. [ABSTRACT FROM AUTHOR]

Sulfate-reducing prokaryotes (SRPs) are essential microorganisms that play crucial roles in various ecological processes. Even though SRPs have been studied for over a century, there are still gaps in our understanding of their biology. In the past two decades, a significant amount of data on SRP ecology has been accumulated. This review aims to consolidate that information, focusing on SRPs in soils, their relation to the rare biosphere, uncultured sulfate reducers, and their interactions with other organisms in terrestrial ecosystems. SRPs in soils form part of the rare biosphere and contribute to various processes as a low-density population. The data reveal a diverse range of sulfate-reducing taxa intricately involved in terrestrial carbon and sulfur cycles. While some taxa like Desulfitobacterium and Desulfosporosinus are well studied, others are more enigmatic. For example, members of the Acidobacteriota phylum appear to hold significant importance for the terrestrial sulfur cycle. Many aspects of SRP ecology remain mysterious, including sulfate reduction in different bacterial phyla, interactions with bacteria and fungi in soils, and the existence of soil sulfate-reducing archaea. Utilizing metagenomic, metatranscriptomic, and culture-dependent approaches will help uncover the diversity, functional potential, and adaptations of SRPs in the global environment. [ABSTRACT FROM AUTHOR]

Purpose: Chain elongation is a metabolic feature that consists of the elongation of short-chain fatty acids to longer and more valuable acids when ethanol is available. To lower the operational costs, the process can also be performed using mixed microbial cultures. However, certain microorganisms in the mixed cultures can use the ethanol provided in competing reactions, which is usually termed excessive ethanol oxidation (EEO). Although minimizing ethanol use is essential, there is a lack of studies analyzing the extent, causes, and solutions to excessive ethanol oxidation processes. Methods: To address this knowledge gap, ethanol, and acetic acid mixtures, at a molar ratio of 5 to 2, were fermented, and the following were analyzed: the fermentation profile at different (1) pH and (2) headspace gas compositions, (3) a 16S analysis of the headspace gas composition fermentations, and (4) a thermodynamic analysis of the reactions involved. Results and Conclusions: All fermentations, except the ones at the lowest pH (5.3), exhibited a significant EEO activity that reduced the yield of chain-elongated products. It was demonstrated that neither the inhibition of methanogenic activity nor the increased H2 partial pressure is an efficient method to inhibit EEO. It was also shown that CO2 can act as an electron acceptor for EEO, promoting the growth of acetogenic bacteria. In the absence of CO2, sulfate was used as an electron acceptor by sulfate-reducing bacteria to facilitate EEO. Methods such as low pH operation with in-line extraction, and the use of alternative sulfur salts, are proposed to increase the ethanol use efficiency in chain elongation processes. [ABSTRACT FROM AUTHOR]

Oil reservoirs represent extreme environments where anaerobic degradation profoundly influences oil composition and quality. Despite the common observation of biodegraded oil, the microbial degradation rates remain largely unknown. To address this knowledge gap, we conducted microcosm incubations with light oil as carbon source, original formation water and sulfate as electron acceptor, closely mimicking in situ conditions to assess oil degradation rates. Samples were taken from a newly drilled oil well to exclude contamination with injection water and allochthonous microorganisms. At the end of the incubations, microbial community analyses with 16S rRNA gene amplicon sequencing revealed the most prominent phyla as Desulfobacterota, Thermotogota, Bacteroidota, Bacillota (formerly Firmicutes), and Synergistota, collectively accounting for up to 44% of relative abundance. Ion chromatography and reverse stable isotope labeling were used to monitor sulfate reduction and CO2 evolution respectively. We calculated an average degradation rate of 0.35 mmol CO2 per year corresponding to 15.2 mmol CO2/mol CH2(oil) per year. This resembles to approximately 200 years to degrade one gram of oil under the applied, presumably ideal conditions. Factoring in the available oil-water-contact (OWC) zone within the incubations yielded a degradation rate of 120 g CH2 m−2 OWC per year, closely aligning with the modeled degradation rates typically observed in oil reservoirs. Moreover, our study highlighted the utility of the reverse stable isotope labeling (RSIL) approach for measuring complex substrate degradation at minute rates. [ABSTRACT FROM AUTHOR]

Abstract This study focused on the chemistry and isotopes of sulfur in lakes. The bottom sediments and water columns of lakes were found to contain reduced forms of sulfur, including hydrogen sulfide ions, elemental sulfur, and thiosulfate ions, along with sulfate ions. It was determined that elemental sulfur in lakes is present mainly in the form of suspensions and colloids, and the proportion of elemental sulfur in polysulfides increases with increasing water pH. It was shown that sulfate reduction results in the greatest isotope fractionation, with a light sulfur isotope accumulating in hydrogen sulfide ions and a heavy sulfur isotope accumulating in sulfate ions. It was confirmed that the abiotic reaction of hydrogen sulfide with oxygen yields a mixture of products that are depleted in 34S and enriched in 34S in hydrogen sulfide. In contrast, the microbial oxidation of HS− → S0 yields zerovalent sulfur, which is 2–4‰ heavier than the initial product. It was shown that the loss of sulfate ions due to bacterial reduction is most significant in subtype-I and subtype-III chloride and soda lakes. In contrast, in subtype-II sulfate and soda lakes, an increase in sulfate ions was noted due to the oxidation of hydrogen sulfides in water-bearing rocks and bacterial hydrogen sulfide. This finding indicated that in addition to evaporation, the formation of a particular type and subtype of saline lake involves the processes of aluminosilicate hydrolysis, sulfate reduction and hydrogen sulfide oxidation.

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur.

This study focused on the chemistry and isotopes of sulfur in lakes. The bottom sediments and water columns of lakes were found to contain reduced forms of sulfur, including hydrogen sulfide ions, elemental sulfur, and thiosulfate ions, along with sulfate ions. It was determined that elemental sulfur in lakes is present mainly in the form of suspensions and colloids, and the proportion of elemental sulfur in polysulfides increases with increasing water pH. It was shown that sulfate reduction results in the greatest isotope fractionation, with a light sulfur isotope accumulating in hydrogen sulfide ions and a heavy sulfur isotope accumulating in sulfate ions. It was confirmed that the abiotic reaction of hydrogen sulfide with oxygen yields a mixture of products that are depleted in 34S and enriched in 34S in hydrogen sulfide. In contrast, the microbial oxidation of HS− → S0 yields zerovalent sulfur, which is 2–4‰ heavier than the initial product. It was shown that the loss of sulfate ions due to bacterial reduction is most significant in subtype-I and subtype-III chloride and soda lakes. In contrast, in subtype-II sulfate and soda lakes, an increase in sulfate ions was noted due to the oxidation of hydrogen sulfides in water-bearing rocks and bacterial hydrogen sulfide. This finding indicated that in addition to evaporation, the formation of a particular type and subtype of saline lake involves the processes of aluminosilicate hydrolysis, sulfate reduction and hydrogen sulfide oxidation. [ABSTRACT FROM AUTHOR]

Quantitatively assessing the porewater dissolved inorganic carbon (DIC) cycling in methane-enriched marine sediments is crucial to understanding the contributions of different carbon sources to the global marine carbon pool. In this study, Makran accretionary wedge was divided into Zone 1 (high methane flux area) and Zone 2 (background area). Porewater geochemical compositions (Cl–, SO4 2–, NH4 +, Mg2+, Ca2+C-DIC) and a reaction-transport model were used to determine the DIC source and calculate the DIC flux through carbonate precipitation and releasing into overlying seawater in sediments. Zone 1 is characterized by the shallower depth of sulfate-methane transition (SMT), where most of porewater sulfate was consumed by anaerobic oxidation of methane (AOM). In contrast, a relatively low flux of methane diffusion in Zone 2 results in a deeper SMT depth and shallow sulfate is predominantly consumed by organoclastic sulfate reduction (OSR). Based on the porewater geochemical profiles and d13C mass balance, the proportions of porewater DIC originating from methane were calculated as 51% in Zone 1 and nearly 0% in Zone 2. An increase of porewater DIC concentration leads to authigenic carbonate precipitation. Solid total inorganic carbon (TIC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) analysis display that carbonate content increases with depth and aragonite appears at or below the depths of SMT. Meanwhile, the flux of DIC released from sediments calculated by the reaction-transport model is 51.3 ~ 90.4 mmol/m² ·yr in Zone 1, which is significantly higher than that in Zone 2 (22.4 mmol/m² ·yr). This study demonstrates that AOM serves as the dominant biogeochemical process regulating the porewater DIC cycle, which has an important impact on the authigenic carbonate burial and the seawater carbonate chemistry. [ABSTRACT FROM AUTHOR]2+, DIC and δ13C-DIC) and a reaction-transport model were used to determine the DIC source and calculate the DIC flux through carbonate precipitation and releasing into overlying seawater in sediments. Zone 1 is characterized by the shallower depth of sulfate-methane transition (SMT), where most of porewater sulfate was consumed by anaerobic oxidation of methane (AOM). In contrast, a relatively low flux of methane diffusion in Zone 2 results in a deeper SMT depth and shallow sulfate is predominantly consumed by organoclastic sulfate reduction (OSR). Based on the porewater geochemical profiles and d13C mass balance, the proportions of porewater DIC originating from methane were calculated as 51% in Zone 1 and nearly 0% in Zone 2. An increase of porewater DIC concentration leads to authigenic carbonate precipitation. Solid total inorganic carbon (TIC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) analysis display that carbonate content increases with depth and aragonite appears at or below the depths of SMT. Meanwhile, the flux of DIC released from sediments calculated by the reaction-transport model is 51.3 ~ 90.4 mmol/m² ·yr in Zone 1, which is significantly higher than that in Zone 2 (22.4 mmol/m² ·yr). This study demonstrates that AOM serves as the dominant biogeochemical process regulating the porewater DIC cycle, which has an important impact on the authigenic carbonate burial and the seawater carbonate chemistry. [ABSTRACT FROM AUTHOR]

Subsurface hydrogen storage would be one of the main possible solutions for a successful energy transition in the future of world energy. However, hydrogen gas is an electron donor which may lead to microbial activity when storing hydrogen in the subsurface. Methanogenesis, acetogenesis, and sulfate reduction are the primary biological reactions that can lead to hydrogen loss through biochemical processes. This paper presents a novel bio-geochemical modelling approach which considers the kinetics of microbial reactions as well as the equilibrated geochemical reactions in the context of underground hydrogen storage. The findings demonstrate that the type of mineralogy and formation water composition may greatly influence biochemical reactions and thus potentially the storage/recovery performance of hydrogen. This study provides a detailed comparison and analysis of the behaviour occurring in calcite, dolomite, and quartz systems assuming the North Sea seawater composition as the in-situ brine. It is found that dolomite is the least favourable mineralogy in terms of hydrogen loss and hydrogen sulfide production, while calcite and quartz are better suited in a seawater-rich environment. • The interplay between biochemical and geochemical reactions during UHS is studied. • There is a strong interplay between biochemical and geochemical reactions. • Small concentrations of sulfate may lead to dangerous level of gas toxicity. [ABSTRACT FROM AUTHOR]

An up-flow anaerobic sludge blanket (UASB) reactor targeting sulfate reduction was operated under a constant TOC/S-SO 4 2− ratio of 1.5 ± 0.3 g C/g S for 639 days using crude glycerol as carbon source. A filamentous and fluffy flocculant material, namely slime-like substances (SLS), was gradually accumulated in the bioreactor after the cease of methanogenic activity. The accumulation of SLS was followed by a decrease in the removal efficiencies and a deterioration in the performance. Selected characteristics of SLS were investigated to explore the causes of its formation and the effect of SLS on the UASB performance. Results showed that glycerol fermentation and sulfate reduction processes taking place in the reactor were mainly accomplished in the bottom part of the UASB reactor, as the sludge concentration in the bottom was higher. The accumulation of SLS in the UASB reactor caused sludge flotation that further led to biomass washout, which decreased the sulfate and glycerol removal efficiencies. Batch activity tests performed with granular sludge (GS), slime-covered granular sludge (SCGS) and SLS showed that there was no difference between GS and SLS in the mechanism of glycerol fermentation and sulfate reduction. However, the specific sulfate reduction rate of GS was higher than that of SLS, while SLS showed a higher glycerol fermentation rate than that of GS. The different rates in GS and SLS were attributed to the higher relative abundances of fermentative microorganisms found in SLS and higher relative abundances of sulfate reducing bacteria (SRB) found in GS. [Display omitted] [ABSTRACT FROM AUTHOR]

We report the formation of minerals from the tochilinite-valleriite group (TVG) during laboratory serpentinization experiments conducted at 300 and 328 °C. Minerals in the TVG are composed of a mixture of sulfide and hydroxide layers that can contain variable proportions of Fe, Mg, Cu, Ni, and other cations in both layers. Members of this group have been observed as accessory minerals in several serpentinites, and have also been observed in association with serpentine minerals in meteorites. To our knowledge, however, TVG minerals have not previously been identified as reaction products during laboratory simulation of serpentinization. The serpentinization experiments reacted olivine with artificial seawater containing 34S-labeled sulfate, with a small amount of solid FeS also added to the 300 °C experiment. In both experiments, the predominant reaction products were chrysotile serpentine, brucite, and magnetite. At 300 °C, these major products were accompanied by trace amounts of the Ni-bearing TVG member haapalaite, Ni,Fe-sulfide (likely pentlandite), and anhydrite. At 328 °C, valleriite occurs rather than haapalaite and the accompanying Ni,Fe-sulfide is proportionally more enriched in Ni. Reduction of sulfate by H2 produced during serpentinization evidently provided a source of reduced S that contributed to formation of the TVG minerals and Ni,Fe-sulfides. The results provide new constraints on the conditions that allow precipitation of tochilinite-valleriite group minerals in natural serpentinites. [ABSTRACT FROM AUTHOR]

A vitamin D receptor (VDR) deficiency leads to the dysbiosis of intestinal bacteria and is associated with various diseases, including cancer, infections, and inflammatory bowel disease. However, the impact of a VDR deficiency on fungi and archaea is unknown. We conditionally deleted the VDR in Paneth cells (VDRΔPC), intestinal epithelial cells (VDRΔIEC), or myeloid cells (VDRΔLyz) in mice and collected feces for shotgun metagenomic sequencing and untargeted metabolomics. We found that fungi were significantly altered in each knockout (KO) group compared to the VDRLoxp control. The VDRΔLyz mice had the most altered fungi species (three depleted and seven enriched), followed by the VDRΔPC mice (six depleted and two enriched), and the VDRΔIEC mice (one depleted and one enriched). The methanogen Methanofollis liminatans was enriched in the VDRΔPC and VDRΔLyz mice and two further archaeal species (Thermococcus piezophilus and Sulfolobus acidocaldarius) were enriched in the VDRΔLyz mice compared to the Loxp group. Significant correlations existed among altered fungi, archaea, bacteria, and viruses in the KO mice. Functional metagenomics showed changes in several biologic functions, including decreased sulfate reduction and increased biosynthesis of cobalamin (vitamin B12) in VDRΔLyz mice relative to VDRLoxp mice. Fecal metabolites were analyzed to examine the involvement of sulfate reduction and other pathways. In conclusion, a VDR deficiency caused the formation of altered fungi and archaea in a tissue- and sex-dependent manner. These results provide a foundation about the impact of a host factor (e.g., VDR deficiency) on fungi and archaea. It opens the door for further studies to determine how mycobiome and cross-kingdom interactions in the microbiome community and metabolites contribute to the risk of certain diseases. [ABSTRACT FROM AUTHOR]

The Tethyan domain hosts the world's most abundant hydrocarbon and Mississippi Valley-type (MVT) Pb-Zn resources. The relations among organic matter-rich sediments, MVT Pb-Zn mineralization, and the Tethyan tectonic evolution history are an important scientific issue. The data of paleogeographic reconstruction indicate that the Proto-, Paleo-, and Neo-Tethys oceans mainly lay in low latitude areas between 30°N and 45°S. The high temperature and precipitation and the lack of sea water overturning in stagnant basins resulted in high marine biological productivity and good preservation conditions for organic matter-rich sediments. Consequently, abundant organic matter-rich sediments were developed and preserved in the Tethyan domain and thus created abundant hydrocarbon resources. Mineralization age data demonstrate that MVT deposits mainly formed during the continent-continent convergence in the late stage of the Tethyan tectonic evolution. Deposits are located in the fold-and-thrust belts and forelands of the continent-continent convergence orogen, and spatially associated with hydrocarbon basins. Organic matter-rich sediments are well developed in MVT ore districts, where hydrocarbon activity appeared earlier than or nearly simultaneous with the Pb-Zn mineralization event. Hydrocarbon activity generally began earlier than the Pb-Zn mineralization in individual deposits. Organic matter-rich sediments and hydrocarbons mainly play the role of reducing agents in the MVT Pb-Zn mineralization process. Through bacterial or thermal reduction, dissolved sulfates from sedimentary strata were reduced to generate reduced sulfur for Pb-Zn sulfide mineralization. In summary, the Tethyan oceans have long been in low latitude areas near the equator, making the Tethyan domain develop abundant organic matter-rich sediments and associated hydrocarbon resources which reduce sulfates to provide sufficient reduced sulfur for MVT Pb-Zn mineralization in the region. [ABSTRACT FROM AUTHOR]

The sulfur biogeochemical cycle controls the sulfur dynamics in the soil. In contrast to almost all deposited sulfur leaching out in temperate catchments, approximately 80% of the deposited S is retained in the catchments in subtropical regions. However, the mechanisms for sulfur retention were unclear, hindering the understanding of potential threats of legacy sulfur with environmental changes. Here, we demonstrated that sulfate reduction (as sulfide fixed in soil) was a prominent yet overlooked mechanism for sulfur retention in addition to the widely recognized sulfate adsorption in soil, based on a study on soil sulfur storage and stable isotope signatures within entire soil profiles in a typical subtropical catchment in China. Using a dual‐isotopic model, the sulfate reduction flux was further determined to be 30% of the S deposition. Due to a lot of deposited sulfur fixed via sulfate reduction, the release of soil legacy sulfur would be less in response to decreasing sulfur deposition compared to the projections only considering adsorption. However, the remobilization of large amounts of reduced S should be regarded as a threat to the environment under climate change in the future. Plain Language Summary: Sulfur budget in catchments reveals substantial retention of around 80% of deposited sulfur in subtropical soils, mitigating acidification arising from heightened sulfur deposition. The substantial sulfur retention was previously ascribed to sulfate adsorption. However, our study unveils sulfate reduction as a prominent yet overlooked retention mechanism, evidenced by soil sulfur storage estimates and stable isotope signatures across complete soil profiles in a typical subtropical Chinese catchment. Sulfate adsorption displays reversibility with declining atmospheric deposition. However, sulfate reduction exhibits relatively stable except during periods of frequent drought attributed to climate change or the soil excavation induced by land‐use change. Key Points: A dual isotopic mass balance model was built to quantify the transformations of S in the ecosystemsSulfur retention accounted for approximately 80% of deposition based on the sulfur input–output budgets for 17 sites in subtropical ChinaSulfate reduction was a prominent mechanism for sulfur retention in addition to widely recognized sulfate adsorption [ABSTRACT FROM AUTHOR]

Gravimetric methods were initially employed to examine the influence of inhibitor IB-1 on the corrosion rate of steel in formation water with oil, which contained hydrogen sulfide, carbon dioxide, and a combination of both. In order to assess the effectiveness of inhibitor IB-1, laboratory tests were conducted using samples of steel of grade St3. Corrosion experiments were conducted within sealed containers with a volume of 0.5 liters, using samples sized 30×20×1 mm. The effectiveness of the IB-1 inhibitor in formation water with oil, containing hydrogen sulfide, carbon dioxide, and a simultaneous presence of hydrogen sulfide and carbon dioxide, exhibited a variation within the ranges of 88.3% to 98.0%, 72.4% to 92.7%, and 60.22% to 94.83%, respectively. The laboratory investigations allowed for the determination of the optimal concentration of inhibitor IB-1 to inhibit the growth of sulfate-reducing bacteria and protect steel of grade St3 from corrosion induced by hydrogen sulfide, carbon dioxide, and the concurrent presence of hydrogen sulfide and carbon dioxide. [ABSTRACT FROM AUTHOR]

The activity of subsurface microorganisms can be harnessed for engineering projects. For instance, the Swiss radioactive waste repository design can take advantage of indigenous microorganisms to tackle the issue of a hydrogen gas (H2) phase pressure build-up. After repository closure, it is expected that anoxic steel corrosion of waste canisters will lead to an H2 accumulation. This occurrence should be avoided to preclude damage to the structural integrity of the host rock. In the Swiss design, the repository access galleries will be back-filled, and the choice of this material provides an opportunity to select conditions for the microbially-mediated removal of excess gas. Here, we investigate the microbial sinks for H2. Four reactors containing an 80/20 (w/w) mixture of quartz sand and Wyoming bentonite were supplied with natural sulfate-rich Opalinus Clay rock porewater and with pure H2 gas for up to 108 days. Within 14 days, a decrease in the sulfate concentration was observed, indicating the activity of the sulfate-reducing bacteria detected in the reactor, e.g., from Desulfocurvibacter genus. Additionally, starting at day 28, methane was detected in the gas phase, suggesting the activity of methanogens present in the solid phase, such as the Methanosarcina genus. This work evidences the development, under in-situ relevant conditions, of a backfill microbiome capable of consuming H2 and demonstrates its potential to contribute positively to the long-term safety of a radioactive waste repository.

Oil reservoirs represent extreme environments where anaerobic degradation profoundly influences oil composition and quality. Despite the common observation of biodegraded oil, the microbial degradation rates remain largely unknown. To address this knowledge gap, we conducted microcosm incubations with light oil as carbon source, original formation water and sulfate as electron acceptor, closely mimicking in situ conditions to assess oil degradation rates. Samples were taken from a newly drilled oil well to exclude contamination with injection water and allochthonous microorganisms. At the end of the incubations, microbial community analyses with 16S rRNA gene amplicon sequencing revealed the most prominent phyla as Desulfobacterota, Thermotogota, Bacteroidota, Bacillota (formerly Firmicutes), and Synergistota, collectively accounting for up to 44% of relative abundance. Ion chromatography and reverse stable isotope labeling were used to monitor sulfate reduction and CO2 evolution respectively. We calculated an average degradation rate of 0.35 mmol CO2 per year corresponding to 15.2 mmol CO2/mol CH2(oil) per year. This resembles to approximately 200 years to degrade one gram of oil under the applied, presumably ideal conditions. Factoring in the available oil-water-contact (OWC) zone within the incubations yielded a degradation rate of 120 g CH2 m−2 OWC per year, closely aligning with the modeled degradation rates typically observed in oil reservoirs. Moreover, our study highlighted the utility of the reverse stable isotope labeling (RSIL) approach for measuring complex substrate degradation at minute rates.

Groundwater contaminated by benzene and toluene is a common issue, posing a threat to the ecosystems and human health. The removal of benzene and toluene under sulfate-reducing condition is well known, but how the bacterial community shifts during this process remains unclear. This study aims to evaluate the shift in bacterial community structure during the biodegradation of benzene and toluene under sulfate-reducing condition. In this study, groundwater contaminated with benzene and toluene were collected from the field and used to construct three artificial samples: Control (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L, and HgCl2 250 mg/L), S1 (benzene 50 mg/L, toluene 1.24 mg/L, sulfate 470 mg/L), and S2 (benzene 100 mg/L, toluene 2.5 mg/L, sulfate 940 mg/L). The contaminants (benzene and toluene), geochemical parameters (sulfate, ORP, and pH), and bacterial community structure in the artificial samples were monitored over time. By the end of this study (day 90), approximately 99% of benzene and 96% of toluene could be eliminated in both S1 and S2 artificial samples, while in the Control artificial sample the contaminant levels remained unchanged due to microbial inactivation. The richness of bacterial communities initially decreased but subsequently increased over time in both S1 and S2 artificial samples. Under sulfate-reducing condition, key players in benzene and toluene degradation were identified as Pseudomonas, Janthinobacterium, Novosphingobium, Staphylococcus, and Bradyrhizobium. The results could provide scientific basis for remediation and risk management strategies at the benzene and toluene contaminated sites.

Black-odorous water is a severe environmental issue that has received continuous attention. The major purpose of the present study was to propose an economical, practical, and pollution-free treatment technology. In this study, the in situ remediation of black-odorous water was conducted by applying different voltages (2.5, 5, and 10 V) to improve oxidation conditions of the surface sediments. The study investigated the effects of voltage intervention on water quality, gas emissions, and microbial community dynamics in surface sediments during the remediation process. The results indicated that the voltage intervention can effectively increase the oxidation–reduction potential (ORP) of the surface sediments and inhibit the emissions of H2S, NH3, and CH4. Moreover, the relative abundances of typical methanogens (Methanosarcina and Methanolobus) and sulfate-reducing bacteria (Desulfovirga) decreased because of the increase in ORP after the voltage treatment. The microbial functions predicted by FAPROTAX also demonstrated the inhibition of methanogenesis and sulfate reduction functions. On the contrary, the total relative abundances of chemoheterotrophic microorganisms (e.g., Dechloromonas, Azospira, Azospirillum, and Pannonibacter) in the surface sediments increased significantly, which led to enhanced biochemical degradability of the black-odorous sediments as well as CO2 emissions. HIGHLIGHTS Voltage intervention contributes to the remediation of black-odorous water.; Applied voltages can effectively improve the oxidation conditions in the sediments.; Voltages significantly inhibited the emissions of H2S, NH3, and CH4 from sediments.; Relative abundances of methanogens and sulfate-reducing bacteria decreased at 10 V.; Abundances of chemoheterotrophic microorganisms increased with increasing voltage.;

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Introduction: Anaerobic oxidation of methane (AOM) is hypothesized to occur through reverse hydrogenotrophic methanogenesis in marine sediments because sulfate reducers pull hydrogen concentrations so low that reverse hydrogenotrophic methanogenesis is exergonic. If true, hydrogenotrophic methanogenesis can theoretically co-occur with sulfate reduction if the organic matter is so labile that fermenters produce more hydrogen than sulfate reducers can consume, causing hydrogen concentrations to rise. Finding accumulation of biologically-produced methane in sulfate-containing organic-rich sediments would therefore support the theory that AOM occurs through reverse hydrogenotrophic methanogenesis since it would signal the absence of net AOM in the presence of sulfate. Methods: 16S rRNA gene libraries were compared to geochemistry and incubations in high depth-resolution sediment cores collected from organic-rich Cape Lookout Bight, North Carolina. Results: We found that methane began to accumulate while sulfate is still abundant (6-8 mM). Methane-cycling archaea ANME-1, Methanosarciniales, and Methanomicrobiales also increased at these depths. Incubations showed that methane production in the upper 16 cm in sulfate-rich sediments was biotic since it could be inhibited by 2-bromoethanosulfonoic acid (BES). Discussion: We conclude that methanogens mediate biological methane production in these organic-rich sediments at sulfate concentrations that inhibit methanogenesis in sediments with less labile organic matter, and that methane accumulation and growth of methanogens can occur under these conditions as well. Our data supports the theory that H2 concentrations, rather than the co-occurrence of sulfate and methane, control whether methanogenesis or AOM via reverse hydrogenotrophic methanogenesis occurs. We hypothesize that the high amount of labile organic matter at this site prevents AOM, allowing methane accumulation when sulfate is low but still present in mM concentrations. [ABSTRACT FROM AUTHOR]

Sulfate is of great importance in anaerobic digestion as its addition can help control the microbial community. In this study, the effect of sulfuric acid addition on the performance of a UASB reactor fed with hydrolyzed starch was investigated. The total organic carbon (TOC), Fe, SO42− removal and methane production were monitored under various chemical oxygen demand (COD) to SO42− ratios, hydraulic retention times (HRTs) and organic loading rates (OLRs). When the HRT was 16 h, and the OLR was equal to 2 g COD/LUASB-day, methane production was 0.24 L CH4/LUASB-day. After the addition of sulfuric acid, TOC removal reached 95%, and the population of Ruminococcus sp. that utilize soluble carbohydrates increased by 19.7%. Nitrogen removal was less than 25%, while the population of Ignavibacterium sp. accounted for 2.3%. When the HRT, OLR and COD/SO42− ratios were equal to 16 h, 2 g COD/LUASB-d and 3.72, respectively, methane production was 0.267 L CH4/LUASB-day. When the OLR increased to 5.94 g, the COD/LUASB-day and COD/SO42− ratios were equal to 12.5, and methane production was three times higher (0.84 L CH4/LUASB-day), with a methane content in the produced biogas greater than 70% due to the increased amount of Methanosaeta sp. and direct interspecies electron transfer. Sulfate addition increased the relative abundance of Desulfovibrio sp., accounting for 9.9% and an iron accumulation exceeding 98.0%. This study indicates that appropriate sulfate concentrations in the feed in combination with the presence of iron in the UASB lead to enhanced methane yields. [ABSTRACT FROM AUTHOR]

The influence of bacterial nutrition (by ethanol) on the appearance of hydrogen sulfide and colloidal sulfur in the filtrate of innovative U-shaped small-sized (point-of-use) submersible denitrifying biofilter describes in the course of its regular operation. The device intends to get drinking water from groundwater sources contaminated with nitrates, sulfates, and heavy metal ions. Colonies of denitrifying bacteria occupy an ecological niche inside the filter bed in an anoxic medium in the inlet elbow of the biofilter and reduce the concentration of nitrates below of hygienic limit at the optimal feed by ethanol. Hydrogen sulfide and colloidal sulfur produce the sulfate-reducing and sulfur bacteria. Sulfate-reducing bacteria act in an anaerobic environment in the bottom conjunction zone of the inlet and outlet elbows of the biofilter. These bacteria release hydrogen sulfide when ethanol adds to filtering water in excess compared to the dosage required for denitrification. Colonies of sulfur bacteria occupy an ecological niche in the output zone of the biofilter exit elbow and oxidise hydrogen sulfide to elemental sulfur. Sulfate reduction associated with nitrates removal can be helpful for additional water purification from admixtures of heavy and polyvalent metal ions. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying bottom sediments of the Lake Trekhtsvetnoe, which is at the meromictic stage of separation from the White Sea (Kandalaksha Bay). The geochemical parameters of bacterial sulfate reduction are considered: the formation and accumulation of different forms of reduced sulfur with respect to the organic matter and reactive iron contents in sediments. The significant content of reduced sulfur compounds (up to 1.47%) and their distribution in the sediments of Lake Trekhtsvetnoe is due to a fairly active sulfate reduction process. The activity of reduction processes is ensured by the input of labile organic matter into sediments, which is formed due to intensively developing microbial communities in the chemocline zone and in the water core of the lake. [ABSTRACT FROM AUTHOR]

The possibility of using heterogeneous construction waste such as masonry rubble as a raw material for the production of lightweight aggregates similar to expanded clays or even pumice has already been reported earlier. This approach has been consistently pursued. As a current aspect, the extent to which gypsum‐containing masonry rubble is also suitable as a raw material was investigated. This not only avoids (expensive) landfilling of this material, but at the same time makes a contribution to at least partially filling the "gypsum gap" created by the elimination of flue gas desulfurization gypsum. The first part of this publication reports on laboratory‐scale tests. The second part focuses on testing the process in the pilot plant. [ABSTRACT FROM AUTHOR]