Dissimilatory Sulfate Reduction Research Articles

Superior nitrate and chromium reduction synergistically driven by multiple electron donors: performance and the related biochemical mechanism

Nitrate and Cr(VI) are the typical and prevalent co-contaminants in the groundwater, how to synchronously and effectively diminish them has received growing attention. The most problem that currently limits the nitrate and Cr(VI) reduction technology for groundwater remediation is with emphasis on exploring the optimal electron donors. This study investigated the feasibility of utilizing the synergistical effect of inorganic electron donors (pyrite, sulfur) and inherently limited organics to promote synchronous nitrate and Cr(VI) removal, which meets the requirement of naturally low-carbon and eco-friendly technologies. The NO3--N and Cr(VI) removal efficiencies in the pyrite and sulfur involved mixotrophic biofilter (PS-BF: approximately 90.8±0.6% and 99.1±2.1%) were substantially higher than that in a volcanic rock supported biofilter (V-BF: about 49.6%±2.8% and 50.0%±9.3%), which was consistent with the spatial variations of their concentrations. Abiotic and biotic batch tests directly confirmed the decisive role of pyrite and sulfur for NO3--N and Cr(VI) removal via chemical and microbial pathways. A server decline in sulfate production correlated with decreasing COD consumption revealed that there was sulfur disproportionation induced by limited organics. Metagenomic analysis suggested that chemoautotrophic microbes like Sulfuritalea and Thiobacillus were key players responsible for sulfur oxidation, nitrate and Cr(VI) reduction. The metabolic pathway analysis suggested that genes encoding functional enzymes related to complete denitrification, S oxidation, and dissimilatory sulfate reduction were upregulated, however, genes encoding Cr(VI) reduction enzymes (e.g. chrA, chrR, nemA, and azoR) were downregulated in PS-BF, which further explained the synergistical effect of multiple electron donors. These findings provide insights into their potential cooperative interaction of multiple electron donors on greatly promoting nitrate and Cr(VI) removal and have implications for the remediation technology of nitrate and Cr(VI) co-contaminated groundwater.

Remediation of heavy metal-contaminated estuarine sediments by strengthening microbial in-situ mineralization

The production of in-situ iron-sulfide minerals through sulfate reduction is commonly used to immobilize heavy metals in sediments and waste residues from abandoned non-ferrous mines. Ensuring a consistent supply of organic carbon sources, such as small molecular organic acids, under optimal reduction conditions, is essential for effective biomineralization. In this study, we developed a technique to enhance the biomineralization (iron-sulfide minerals) capacity of native sulfate-reducing bacteria to immobilize heavy metals, using the facultative anaerobic fermentation bacterium Bacillus coagulans to bind to waste olivine, providing small molecular organic acids required by sulfate-reducing bacteria while providing more reduction conditions for remediation systems.Our results showed that, compared with the control group (Control) and the group added with medium (Cul), the groups added with Bacillus coagulans (Cul + Bio) and the combination of Bacillus coagulans and olivine (Cul + Bio + Oli), significantly increased the overlying water pH value, pH remained above 8 in the final stage of remediation, and decreased the redox potential and sulfate concentration, ORP remained −80 mV, SO42− concentration below 600 mg/L at the end of remediation. The addition of Bacillus coagulans and olivine helped stabilize heavy metals Cu, Pb, Zn, and Cd by reducing their release into the liquid phase. Cd and Pb were found to be in more stable forms within the solid phase. In the Cul + Bio and Cul + Bio + Oli groups, sulfur primarily existed as more reductive FeS, accounting for 55% and 75% of the sulfur speciations, respectively. Desulfuromonadia, Desulfuromonas, Desulfofustis, and Geothermobacter have been identified in the Cul + Bio + Oli experimental group in high abundance and are capable of dissimilatory sulfate reduction. The combined application of microorganisms and waste olivine offers an effective strategy for remediating in-situ heavy metal-contaminated soils/sediments, thereby establishing a theoretical and practical foundation for employing microbial mineralization in the in-situ remediation of heavy metals in sediment.

Reaction Mechanism Catalyzed by the Dissimilatory Sulfite Reductase - The Role of the Siroheme-[4FeS4] Cofactor.

The present work is another part of our investigation on the pathway of dissimilatory sulfate reduction and covers a theoretical study on the reaction catalyzed by dissimilatory sulfite reductase (dSIR). dSIR is the terminal enzyme involved in this metabolic pathway, which uses the siroheme-[4Fe4S] cofactor for six-electron reduction of sulfite to sulfide. In this study we use a large cluster model containing siroheme-[4Fe4S] cofactor and protein residues involved in the direct interactions with the substrate, to get insight into the most feasible reaction mechanism and to understand the role of each considered active site component. In combination with earlier studies reported in the literature, our results lead to several interesting insights. One of the most important conclusions is that the reaction mechanism consists of three steps of two-electron reduction of sulfur and the probable role of the siroheme-[4Fe4S] cofactor is to ensure the delivery of packages of two electrons to the reactant.

Anaerobic ammonium oxidation coupled with sulfate reduction links nitrogen with sulfur cycle

Sulfate-dependent ammonium oxidation (Sulfammox) is a critical process linking nitrogen and sulfur cycles. However, the metabolic pathway of microbes driven Sulfammox is still in suspense. The study demonstrated that ammonium was not consumed with sulfate as the sole electron acceptor during long-term enrichment, probably due to inhibition from sulfide accumulation, while ammonium was removed at ∼ 10 mg N/L/d with sulfate and nitrate as electron acceptors. Ammonium and sulfate were converted into nitrogen gas, sulfide, and elemental sulfur. Sulfammox was mainly performed by Candidatus Brocadia sapporoensis and Candidatus Brocadia fulgida, both of which encoded ammonium oxidation pathway and dissimilatory sulfate reduction pathway. Not sulfide-driven autotrophic denitrifiers but Candidatus Kuenenia stuttgartiensis converted nitrate to nitrite with sulfide. The results of this study reveal the specialized metabolism of Sulfammox bacteria (Candidatus Brocadia sapporoensis and Candidatus Brocadia fulgida) and provide insight into microbial relationships during the nitrogen and sulfur cycles.

Characteristics and mechanisms of phosphine production in sulfur-based constructed wetlands

Phosphine (PH3) is an important contributor to the phosphorus cycle and is widespread in various environments. However, there are few studies on PH3 in constructed wetlands (CWs). In this study, lab-scale CWs and batch experiments were conducted to explore the characteristics and mechanisms of PH3 production in sulfur-based CWs. The results showed that the PH3 release flux of sulfur-based CWs varied from 0.86±0.04 ng·m−2·h−1 to 1.88±0.09 ng·m−2·h−1. The dissolved PH3 was the main PH3 form in CWs and varied from 2.73 μg·L−1 to 4.08 μg·L−1. The matrix-bound PH3 was a staging reservoir for PH3 and increased with substrate depth. In addition, the sulfur-based substrates had a significant improvement on PH3 production. Elemental sulfur is more conducive to PH3 production than pyrite. Moreover, there was a significant positive correlation between PH3 production, the dsrB gene, and nicotinamide adenine dinucleotide (NADH). NADH might catalyze the phosphate reduction process. And the final stage of the dissimilatory sulfate reduction pathway driven by the dsrB gene might also provide energy for phosphate reduction. The migration and transformation of PH3 increased the available P (Resin-P and NaHCO3-P) from 35 % to 56 % in sulfur-based CW, and the P adsorption capacity was improved by 12 %. The higher proportion of available P increased the plant uptake rate of P by 17 %. This study improves the understanding of the phosphorus cycle in sulfur-based CW and provides new insight into the long-term stable operation of CWs.

Speciation and Possible Origins of Organosulfur Compounds in Rice Paddy Soils Affected by Acid Mine Drainage.

Although sulfur cycling in acid mine drainage (AMD)-contaminated rice paddy soils is critical to understanding and mitigating the environmental consequences of AMD, potential sources and transformations of organosulfur compounds in such soils are poorly understood. We used sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy to quantify organosulfur compounds in paddy soils from five AMD-contaminated sites and one AMD-uncontaminated reference site near the Dabaoshan sulfide mining area in South China. We also determined the sulfur stable isotope compositions of water-soluble sulfate (δ34SWS), adsorbed sulfate (δ34SAS), fulvic acid sulfur (δ34SFAS), and humic acid sulfur (δ34SHAS) in these samples. Organosulfate was the dominant functional group in humic acid sulfur (HAS) in both AMD-contaminated (46%) and AMD-uncontaminated paddy soils (42%). Thiol/organic monosulfide contributed a significantly lower proportion of HAS in AMD-contaminated paddy soils (8%) compared to that in AMD-uncontaminated paddy soils (21%). Within contaminated soils, the concentration of thiol/organic monosulfide was positively correlated with cation exchange capacity (CEC), moisture content (MC), and total Fe (TFe). δ34SFAS ranged from -6.3 to 2.7‰, similar to δ34SWS (-6.9 to 8.9‰), indicating that fulvic acid sulfur (FAS) was mainly derived from biogenic S-bearing organic compounds produced by assimilatory sulfate reduction. δ34SHAS (-11.0 to -1.6‰) were more negative compared to δ34SWS, indicating that dissimilatory sulfate reduction and abiotic sulfurization of organic matter were the main processes in the formation of HAS.

Increasing temperature and sulfate enhances the efficiency of methane abatement in an anaerobic oxidation of methane bioreactor (AOMB) system

Controlling methane emission sources is important for the sustainable application of energy from the deep sea to alleviate methane-induced global warming. The anaerobic oxidation of methane (AOM) process coupled with sulfate reduction (SR) plays a key role in seafloor methane biofiltration. However, the mechanisms for the enhancement of the methane abatement efficiency in an AOM reaction system and the responses of temperature and sulfate concentration remain known. To cover the knowledge gap, this study investigated the enhancement of methane abatement in a self-manufactured AOMB system for 230 days via increasing temperatures and sulfate concentrations. The primary conclusions are as follows: (a) AOM and SR rates were significantly elevated at the conditions of temperature increase (8 to 15 °C) and sulfate addition (+15 mM). (b) Sulfate and temperature were key factors influencing the diversity of archaea and bacterial communities. (c) ANME-2c, ANME-1b, SEEP-SRB1, and Halodesulfovibrio were dominant genera of methane‑sulfur cycling in the system. (d) Functional gene prediction revealed that the coupling of methane oxidation and dissimilatory sulfate reduction was responsible for the methane abatement. Our findings provide new insights into the enhancement of methane abatement efficiency in the deep sea and the application of AOM reaction systems.

Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria.

Phytoplankton blooms fuel marine food webs with labile dissolved carbon and also lead to the formation of particulate organic matter composed of living and dead algal cells. These particles contribute to carbon sequestration and are sites of intense algal-bacterial interactions, providing diverse niches for microbes to thrive. We analyzed 16S and 18S ribosomal RNA gene amplicon sequences obtained from 51 time points and metaproteomes from 3 time points during a spring phytoplankton bloom in a shallow location (6-10m depth) in the North Sea. Particulate fractions larger than 10µm diameter were collected at near daily intervals between early March and late May in 2018. Network analysis identified two major modules representing bacteria co-occurring with diatoms and with dinoflagellates, respectively. The diatom network module included known sulfate-reducing Desulfobacterota as well as potentially sulfur-oxidizing Ectothiorhodospiraceae. Metaproteome analyses confirmed presence of key enzymes involved in dissimilatory sulfate reduction, a process known to occur in sinking particles at greater depths and in sediments. Our results indicate the presence of sufficiently anoxic niches in the particle fraction of an active phytoplankton bloom to sustain sulfate reduction, and an important role of benthic-pelagic coupling for microbiomes in shallow environments. Our findings may have implications for the understanding of algal-bacterial interactions and carbon export during blooms in shallow-water coastal areas.

A bioaugmentation strategy to recover methane production under sulfate-stressed conditions: Highlights on targeted sulfate-reducing bacteria and DIET-related species

Bioaugmentation has been recognized as a key strategy to improve the anaerobic digestion efficiency in organic waste treatment. Methanosarcina barkeri possesses direct interspecies electron transfer capability, a characteristic that allows it to outcompete other unwanted species such as sulfate-reducing bacteria. This study investigated the effects of bioaugmentation with Methanosarcina barkeri DSM800 on two continuous-stirred tank reactors fed with a sulfate-rich feedstock. One of the two reactors was supplemented with magnetite to facilitate direct interspecies electron transfer. Time series quantitative polymerase chain reactions were performed to evaluate the absolute abundance of crucial species, including the augmented Methanosarcina. Results showed increased and stabilized methane production of 22% and 21% in the reactor amended with magnetite and in the control reactor, respectively. Moreover, volatile fatty acids were almost completely consumed in the magnetite-supplemented reactor. The quantitative polymerase chain reaction was used to analyze the abundance of targeted species in response to bioaugmentation. Specifically, Methanosarcina barkeri was not retained in either reactor after one hydraulic retention time. Direct interspecies electron transfer-associated microorganisms showed opposite trends in the two reactors, highlighting the different interactions with Methanosarcina barkeri in the presence and absence of magnetite. Sulfate-reducing bacteria following the dissimilatory sulfate reduction pathway exhibited an opposite behavior in the reactor amended with magnetite, in contrast to those employing the assimilatory sulfate reduction pathway. Overall, the study demonstrated that bioaugmentation with exogenous archaea can considerably alter the microbial community, but the introduced species is not able to establish itself in a stable microbiome. In addition, the strategy could be further tested to control H2S production in real-world waste treatment scenarios. Quantitative polymerase chain reaction proved to be a useful tool for monitoring changes in the absolute abundance of microorganisms in bioreactors, implementing effective monitoring and control strategies to improve overall system performance.

Re‐Evaluating Hydrogen Sulfide as a Sink for Cadmium and Zinc in the Oxic to Suboxic Upper Water Column of the Pacific Ocean

AbstractHydrogen sulfide is produced by heterotrophic bacteria in anoxic waters and via carbonyl sulfide hydrolysis and phytoplankton emissions under oxic conditions. Apparent losses of dissolved cadmium (dCd) and zinc (dZn) in oxygen minimum zones (OMZs) of the Atlantic and Pacific Oceans have been attributed to metal‐sulfide precipitation formed via dissimilatory sulfate reduction. It has also been argued that such a removal process could be a globally important sink for dCd and dZn. However, our studies from the North Pacific OMZ show that dissolved and particulate sulfide concentrations are insufficient to support the removal of dCd via precipitation. In contrast, apparent dCd and dZn deficits in the eastern tropical South Pacific OMZ do reside in the oxycline with particulate sulfide maxima, but they also coincide with the secondary fluorescence maxima, suggesting that removal via sulfide precipitation may be due to a combination of dissimilatory and assimilatory sulfate reduction. Notably, dCd loss via precipitation with sulfide from assimilatory reduction was found in upper oxic waters of the North Pacific. While dissimilatory sulfate reduction may explain local dCd and dZn losses in some OMZs, our evaluation of North Pacific OMZs demonstrates that dCd and dZn losses are unlikely to be a globally relevant sink. Nevertheless, metal sulfide losses due to assimilatory sulfate reduction in surface waters should be considered in future biogeochemical models of oceanic Cd (and perhaps Zn) cycling.

A Synthetic Microbiome Based on Dominant Microbes in Wild Rice Rhizosphere to Promote Sulfur Utilization

Sulfur (S) is one of the main components of important biomolecules, which has been paid more attention in the anaerobic environment of rice cultivation. In this study, 12 accessions of rice materials, belonging to two Asian rice domestication systems and one African rice domestication system, were used by shotgun metagenomics sequencing to compare the structure and function involved in S cycle of rhizosphere microbiome between wild and cultivated rice. The sulfur cycle functional genes abundances were significantly different between wild and cultivated rice rhizosphere in the processes of sulfate reduction and other sulfur compounds conversion, implicating that wild rice had a stronger mutually-beneficial relationship with rhizosphere microbiome, enhancing sulfur utilization. To assess the effects of sulfate reduction synthetic microbiomes, Comamonadaceae and Rhodospirillaceae, two families containing the genes of two key steps in the dissimilatory sulfate reduction, aprA and dsrA respectively, were isolated from wild rice rhizosphere. Compared with the control group, the dissimilatory sulfate reduction in cultivated rice rhizosphere was significantly improved in the inoculated with different proportions groups. It confirmed that the synthetic microbiome can promote the S-cycling in rice, and suggested that may be feasible to construct the synthetic microbiome step by step based on functional genes to achieve the target functional pathway. In summary, this study reveals the response of rice rhizosphere microbial community structure and function to domestication, and provides a new idea for the construction of synthetic microbiome.

Multi-omics insights into biogeochemical responses to organic matter addition in an acidic pit lake: Implications for bioremediation

Acidic pit lakes (APLs) emerge as reservoirs of acid mine drainage in flooded open-pit mines, representing extreme ecosystems and environmental challenges worldwide. The bioremediation of these oligotrophic waters necessitates the addition of organic matter, but the biogeochemical response of APLs to exogenous organic matter remains inadequately comprehended. This study delves into the biogeochemical impacts and remediation effects of digestate-derived organic matter within an APL, employing a multi-omics approach encompassing geochemical analyses, amplicon and metagenome sequencing, and ultra-high resolution mass spectrometry. The results indicated that digestate addition first stimulated fungal proliferation, particularly Ascomycetes and Basidiomycetes, which generated organic acids through lignocellulosic hydrolysis and fermentation. These simple compounds further supported heterotrophic growth, including Acidiphilium, Acidithrix, and Clostridium, thereby facilitating nitrate, iron, and sulfate reduction linked with acidity consumption. Nutrients derived from digestate also promoted the macroscopic development of acidophilic algae. Notably, the increased sulfate reduction-related genes primarily originated from assimilatory metabolism, thus connecting sulfate decrease to organosulfur increase. Assimilatory and dissimilatory sulfate reduction collectively contributed to sulfate removal and metal fixation. These findings yield multi-omics insights into APL biogeochemical responses to organic matter addition, enhancing the understanding of carbon-centered biogeochemical cycling in extreme ecosystems and guiding organic amendment-based bioremediation in oligotrophic polluted environments.

Deep-sea in situ and laboratory multi-omics provide insights into the sulfur assimilation of a deep-sea Chloroflexota bacterium.

The cycling of sulfur is one of Earth's major biogeochemical processes and is closely related to the energy metabolism of microorganisms living in the deep-sea cold seep and hydrothermal vents. To date, some of the members of Chloroflexota are proposed to play a previously unrecognized role in sulfur cycling. However, the sulfur metabolic characteristics of deep-sea Chloroflexota bacteria have never been reported, and remain to be verified in cultured deep-sea representatives. Here, we show that the deep-sea Chloroflexota bacterium ZRK33 can perform sulfate assimilation in both laboratory and deep-sea conditions, which expands our knowledge of the sulfur metabolic potential of deep-sea Chloroflexota bacteria. We also show that the genes associated with assimilatory and dissimilatory sulfate reduction ubiquitously distribute in the deep-sea Chloroflexota members, providing hints to the roles of Chloroflexota bacteria in deep-sea sulfur biogeochemical cycling.

DsrMKJOP is the terminal reductase complex in anaerobic sulfate respiration

Microbial dissimilatory sulfate reduction (DSR) is a key process in the Earth biogeochemical sulfur cycle. In spite of its importance to the sulfur and carbon cycles, industrial processes, and human health, it is still not clear how reduction of sulfate to sulfide is coupled to energy conservation. A central step in the pathway is the reduction of sulfite by the DsrAB dissimilatory sulfite reductase, which leads to the production of a DsrC-trisulfide. A membrane-bound complex, DsrMKJOP, is present in most organisms that have DsrAB and DsrC, and its involvement in energy conservation has been inferred from sequence analysis, but its precise function was so far not determined. Here, we present studies revealing that the DsrMKJOP complex of the sulfate reducer Archaeoglobus fulgidus works as a menadiol:DsrC-trisulfide oxidoreductase. Our results reveal a close interaction between the DsrC-trisulfide and the DsrMKJOP complex and show that electrons from the quinone pool reduce consecutively the DsrM hemes b, the DsrK noncubane [4Fe-4S]3+/2+ catalytic center, and finally the DsrC-trisulfide with concomitant release of sulfide. These results clarify the role of this widespread respiratory membrane complex and support the suggestion that DsrMKJOP contributes to energy conservation upon reduction of the DsrC-trisulfide in the last step of DSR.

Microbiological and geochemical characterization of As-bearing tailings and underlying sediments

Over the past 100 years, extensive oxidation of As-bearing sulfide-rich tailings from the abandoned Long Lake Gold Mine (Canada) has resulted in the formation of acid mine drainage (pH 2.0–3.9) containing high concentrations of dissolved As (∼400 mg L−1), SO42-, Fe and other metals. Dissolved As is predominantly present as As(III), with increased As(V) near the tailings surface. Pore-gas O2 is depleted to < 1 vol% in the upper 30–80 cm of the tailings profile. The primary sulfides, pyrite and arsenopyrite, are highly oxidized in the upper portions of the tailings. Elevated proportions of sulfide-oxidizing prokaryotes are present in this zone (mean 32.3% of total reads). The tailings are underlain by sediments rich in organic C. Enrichment in δ34S-SO4 in pore-water samples in the organic C-rich zone is consistent with dissimilatory sulfate reduction. Synchrotron-based spectroscopy indicates an abundance of ferric arsenate phases near the impoundment surface and the presence of secondary arsenic sulfides in the organic-C beneath the tailings. The persistence of elevated As concentrations beneath the tailings indicates precipitation of secondary As sulfides is not sufficient to completely remove dissolved As. The oxidation of sulfides and release of As is expected to continue for decades. The findings will inform future remediation efforts and provide a foundation for the long-term monitoring of the effectiveness of the remediation program.

Underlying the inhibition mechanisms of sulfate and lincomycin on long-term anaerobic digestion: Microbial response and antibiotic resistance genes distribution

This study evaluated the resilience of a long-term anaerobic treatment system exposed to sulfate, lincomycin (LCM) and their combined stress. LCM was found to impede anaerobic propionate degradation, while sulfate for restraining methanogenic acetate utilization. The combined stress, with influent LCM of 200 mg/L and sulfate of 1404 mg/L, revealed severer inhibition on anaerobic digestion than individual inhibition, leading to 73.9 % and 38.5 % decrease in methane production and sulfate removal, respectively. Suppression on propionate-oxidizing bacteria like unclassified_f__Anaerolineae and unclassified_f__Syntrophaceae further demonstrated LCM's inhibitory effect on propionate degradation. Besides, the down-regulation of genes encoding dissimilatory sulfate reduction enzymes caused by LCM triggered great inhibition on sulfate reduction. A notable increase in ARGs was detected under sulfate-stressed condition, owing to its obvious enrichment of tetracycline-resistant genes. Genera including unclassified_f__Syntrophaceae, unclassified_f__Geobacteraceae and unclassified_f__Anaerolineaceae were identified as dominant host of ARGs and enriched by sulfate addition. Overall, these results could provide the theoretical basis for further enhancement on anaerobic digestion of pharmaceutical wastewater containing sulfate and lincomycin.

Immobilisation of Molybdenum in a Sulphate-Reducing Bioreactor

This work presents a biological remediation process for molybdenum-bearing wastewater which may lead to the fabrication of biogenic Mo chalcogenide particles with (photo)catalytic properties. The process is based on dissimilatory sulphate reduction, utilising sulphate-reducing bacteria (SRB), and reductive precipitation of molybdate which is the predominant species of molybdenum in oxygenated water/wastewater. The SRB culture was established in a biofilm reactor which was fed with synthetic solutions containing sulphate (17.7 mM), molybdate molybdenum (2 mM), divalent iron (1.7 mM) and ethanol as the carbon/electron donor. The performance of the bioreactor was monitored in terms of pH, sulphate and molybdenum (Mo(VI) and total) content. The presence of thiomolybdate species was studied by scanning UV-Vis absorbance of samples from the reactor outflow while the reactor precipitates were studied via electron microscopy coupled with energy dispersive spectrometry, X-ray diffractometry and laser light scattering. A molar molybdate/sulphate ratio of 1:12.5 proved effective for molybdate reduction and recovery by 76% in 96 h, whereas sulphate was reduced by 57%. Molybdenum was immobilised in the sulphidic precipitates of the bioreactor, presumably via two principal mechanisms: (i) microbially mediated reduction and precipitation, and (ii) thiomolybdate formation and sorption/incorporation into iron sulphides.

Altering environmental conditions induce shifts in simulated deep terrestrial subsurface bacterial communities-Secretion of primary and secondary metabolites.

The deep terrestrial subsurface (DTS) harbours a striking diversity of microorganisms. However, systematic research on microbial metabolism, and how varying groundwater composition affects the bacterial communities and metabolites in these environments is lacking. In this study, DTS groundwater bacterial consortia from two Fennoscandian Shield sites were enriched and studied. We found that the enriched communities from the two sites consisted of distinct bacterial taxa, and alterations in the growth medium composition induced changes in cell counts. The lack of an exogenous organic carbon source (ECS) caused a notable increase in lipid metabolism in one community, while in the other, carbon starvation resulted in low overall metabolism, suggesting a dormant state. ECS supplementation increased CO2 production and SO4 2- utilisation, suggesting activation of a dissimilatory sulphate reduction pathway and sulphate-reducer-dominated total metabolism. However, both communities shared common universal metabolic features, most probably involving pathways needed for the maintenance of cell homeostasis (e.g., mevalonic acid pathway). Collectively, our findings indicate that the most important metabolites related to microbial reactions under varying growth conditions in enriched DTS communities include, but are not limited to, those linked to cell homeostasis, osmoregulation, lipid biosynthesis and degradation, dissimilatory sulphate reduction and isoprenoid production.

Contribution of sulfate-reducing bacteria in the formation of hydrogen sulfide in coal seams of Hancheng mining area, China

Coalbed hydrogen sulfide (H2S) is a toxic and corrosive gas, it’s very important for researching the origin of H2S in coalbed and related metabolic characteristics of microbes in the bioconversion of coal. The purpose of this study is to clarify the contribution and influencing factors of bacterial and sulfate-reducing bacterial (SRB) communities in the Taiyuan Formation (Nos. 5 and 11 coal seams) of the Hancheng mining area, by using gas composition testing, water quality measurements, 16S rRNA amplicon sequencing, and fluorescence real-time quantitative (qPCR) analysis. The results indicate that the coal seam gas is mainly composed of methane with a trace amount of H2S ranging from 4 to 56 ppm. The H2S content exhibits a positive correlation with the SRB gene copy number within the range of ∼30 to 200 copies/mL, indicating a strong association between the production of H2S and the contribution of SRB in the study area. The presence of Desulfobulbus, Desulfovibrio, Desulfomicrobium, Desulfotomaculum, Desulfobacca, Thermosinus, Desulfococcus, Desulfarculus, and Syntrophobacter genus from the coalbed-produced water further proves that H2S is reduced in dissimilatory sulfate reduction (DSR) pathway. Bacteria and SRB play a critical role in the conversion of coal organic matter through biodegradation. SRB community composition is more related to total organic carbon, total dissolved solids, and trace elements. This study gives an in-depth explanation of the formation of H2S in coalbed and provides novel views in toxic gas removal in future gas exploitation.

Sulfate distribution and sulfate reduction in global marine sediments

The quantification of anaerobic oxidation of organic matter in the global seabed is to a large extent based on transport-reaction modeling of pore water ions involved in the mineralization processes. As the predominant of these processes, sulfate reduction can be modeled from the depth distribution of sulfate and other relevant solutes. An active organoclastic sulfate reduction is typically characterized by sulfate profiles with a concave-down shape. We use here a comprehensive database to show that half of all competent sulfate profiles have an opposite, concave-up shape, which may appear inconsistent with this concept. We also show that there is a strong discrepancy between sulfate profiles obtained by gravity coring and by IODP coring, with generally much higher sulfate flux and shallower sulfate penetration depth in the gravity cores (the term IODP here covers the international ocean drilling programs, DSDP, ODP and IODP). The discrepancy is correlated with a selectivity for coring sites in the published studies, by which gravity coring is focused towards the ocean margins and continental shelf and towards high surface water productivity and high sedimentation rate. In contrast, IODP coring is more frequently done in low sedimentation regions and is largely absent from the continental shelf. As a result, estimates of sulfate reduction in the global seabed may be biased by a selection of only IODP core data for the modeling. Furthermore, the modeling of pore water profiles shows net rates of sulfate reduction, while 35S-radiotracer experiments show the higher gross rates of the process. Estimates from 35S-radiotracer measurements suggest that dissimilatory sulfate reduction oxidizes 77 Tmol yr−1 of organic carbon globally, which is 3- to 4-fold higher than recent data based on modeling of IODP data. The potential biases by global estimates of sulfate reduction in marine sediments are discussed.