The role of sulfur cycle in new particle formation: Cycloaddition reaction of SO3 to H2S.

The chemistry of sulfur cycle contributes significantly to the atmospheric nucleation process, which is the first step of new particle formation (NPF). In the present study, cycloaddition reaction mechanism of sulfur trioxide (SO3) to hydrogen sulfide (H2S) which is a typical air pollutant and toxic gas detrimental to the environment were comprehensively investigate through theoretical calculations and Atmospheric Cluster Dynamic Code simulations. Gas-phase stability and nucleation potential of the product thiosulfuric acid (H2S2O3, TSA) were further analyzed to evaluate its atmospheric impact. Without any catalysts, the H2S + SO3 reaction is infeasible with a barrier of 24.2 kcal/mol. Atmospheric nucleation precursors formic acid (FA), sulfuric acid (SA), and water (H2O) could effectively lower the reaction barriers as catalysts, even to a barrierless reaction with the efficiency of cis-SA > trans-FA > trans-SA > H2O. Subsequently, the gas-phase stability of TSA was investigated. A hydrolysis reaction barrier of up to 61.4 kcal/mol alone with an endothermic isomerization reaction barrier of 5.1 kcal/mol under the catalytic effect of SA demonstrates the sufficient stability of TSA. Furthermore, topological and kinetic analysis were conducted to determine the nucleation potential of TSA. Atmospheric clusters formed by TSA and atmospheric nucleation precursors (SA, ammonia NH3, and dimethylamine DMA) were thermodynamically stable. Moreover, the gradually decreasing evaporation coefficients for TSA-base clusters, particularly for TSA-DMA, suggests that TSA may participate in NPF where the concentration of base molecules are relatively higher. The present new reaction mechanism may contributes to a better understanding of atmospheric sulfur cycle and NPF.

Effect of nitrogen oxides and sulfur oxides to triphenyl phosphate degradation and cytotoxicity on surface of different transition metal salts.

Nitrogen oxides and sulfur oxides, as the dominant toxic gases in the atmosphere, can induce severe human health problems under the composite pollutant conditions. Currently the effect of nitrogen or sulfur oxides in atmospheric environment to the degradation and cytotoxicity of triphenyl phosphate (TPhP) on atmospheric particle surfaces still remain poorly understood. Hence, laboratory simulation methods were used in this study to investigate the effect and related mechanism. First, particle samples were prepared with the TPhP coated on MnSO4, CuSO4, FeSO4 and Fe2(SO4)3 surface. The results showed that, when nitrogen or sulfur oxides were present, more significant TPhP degradation on all samples can be observed under both light and dark conditions. The results proved nitrogen oxides and sulfur oxides were the vital influence factors to the degradation of TPhP, which mainly promoted the OH generation in the polluted atmosphere. The mechanism study indicated that diphenyl hydrogen phosphate (DPhP) and OH-DPhP were two main stable degradation products. These degradation products originated from the phenoxy bond cleavage and hydroxylation of TPhP caused by hydroxyl radicals. In addition, no TPhP related organosulfates (OSs) or organic nitrates (ON) formation were observed. Regarding the cytotoxicity, all the particles can induce more significant cellular injury and apoptosis of A549 cells, which may be relevant to the adsorbed nitrogen oxides or sulfur oxides on particles surfaces. The superfluous reactive oxygen species (ROS) generation was the possible reason of cytotoxicity. This research can supply a comprehensive understanding of the promoting effect of nitrogen and sulfur oxides to TPhP degradation and the composite cytotoxicity of atmospheric particles.

Chalcogen Noncovalent Interactions between Diazines and Sulfur Oxides in Supramolecular Circular Chains.

The noncovalent chalcogen interaction between SO2/SO3 and diazines was studied through a dispersion-corrected DFT Kohn-Sham molecular orbital together with quantitative energy decomposition analyses. For this, supramolecular circular chains of up to 12 molecules were built with the aim of checking the capability of diazine molecules to detect SO2/SO3 compounds within the atmosphere. Trends in the interaction energies with the increasing number of molecules are mainly determined by the Pauli steric repulsion involved in these σ-hole/π-hole interactions. But more importantly, despite the assumed electrostatic nature of the involved interactions, the covalent component also plays a determinant role in its strength in the involved chalcogen bonds. Noticeably, π-hole interactions are supported by the charge transfer from diazines to SO2/SO3 molecules. Interaction energies in these supramolecular complexes are not only determined by the S···N bond lengths but attractive electrostatic and orbital interactions also determine the trends. These results should allow us to establish the fundamental characteristics of chalcogen bonding based on its strength and nature, which is of relevance for the capture of sulfur oxides.

Biochemical characterization and cleavage specificities analyses of three endo-1,3-fucanases within glycoside hydrolase family 174.

Sulfated fucans have garnered extensive research interest in recent decades due to their varied bioactivity. Fucanases are important tools for investigating sulfated fucans. This study reported the bioinformatic analysis and biochemical properties of three GH174 family endo-1,3-fucanases. Wherein, Fun174Rm and Fun174Sb showed the highest optimal reaction temperature among the reported fucanases, and Fun174Sb possessed favorable thermostability and catalysis efficiency. Fun174Rm displayed a random endo-acting manner, while Fun174Ri and Fun174Sb hydrolyzed sulfated fucan in processive manners. UPLC-MS and NMR analyses confirmed that the three enzymes catalyze cleavage of the α(1 â†’ 3)-bonds between Fucp2S and Fucp2S in the sulfated fucan from Isostichopus badionotus. These enzymes demonstrated novel cleavage specificities, which could accept α-Fucp2S residues at subsites -1 and + 1. The acquiring of these biotechnological tools would be beneficial to the in-depth research of sulfated fucans.

Long-term exposure to fine particulate matter constituents in relation to chronic kidney disease: evidence from a large population-based study in China.

The effects of long-term exposure to fine particulate matter (PM2.5) constituents on chronic kidney disease (CKD) are not fully known. This study sought to examine the association between long-term exposure to major PM2.5 constituents and CKD and look for potential constituents contributing substantially to CKD. This study included 81,137 adults from the 2018 to 2019 baseline survey of China Multi-Ethnic Cohort. CKD was defined by the estimated glomerular filtration rate. Exposure concentration data of 7 major PM2.5 constituents were assessed by satellite remote sensing. Logistic regression models were used to estimate the effect of each PM2.5 constituent exposure on CKD. The weighted quantile sum regression was used to estimate the effect of mixed exposure to all constituents. PM2.5 constituents had positive correlations with CKD (per standard deviation increase), with ORs (95% CIs) of 1.20 (1.02-1.41) for black carbon, 1.27 (1.07-1.51) for ammonium, 1.29 (1.08-1.55) for nitrate, 1.20 (1.01-1.43) for organic matter, 1.25 (1.06-1.46) for sulfate, 1.30 (1.11-1.54) for soil particles, and 1.63 (1.39-1.91) for sea salt. Mixed exposure to all constituents was positively associated with CKD (1.68, 1.32-2.11). Sea salt was the constituent with the largest weight (0.36), which suggested its importance in the PM2.5-CKD association, followed by nitrate (0.32), organic matter (0.18), soil particles (0.10), ammonium (0.03), BC (0.01). Sulfate had the least weight (< 0.01). Long-term exposure to PM2.5 sea salt and nitrate may contribute more than other constituents in increasing CKD risk, providing new evidence and insights for PM2.5-CKD mechanism research and air pollution control strategy.

Cu/Biochar Bifunctional Catalytic Removal of COS and H2S:H2O Dissociation and CuO Anchoring Enhanced by Pyridine N.

Economic and environmentally friendly strategies are needed to promote the bifunctional catalytic removal of carbonyl sulfide (COS) by hydrolysis and hydrogen sulfide (H2S) by oxidation. N doping is considered to be an effective strategy, but the essential and intrinsic role of N dopants in catalysts is still not well understood. Herein, the conjugation of urea and biochar during Cu/biochar annealing produced pyridine N, which increased the combined COS/H2S capacity of the catalyst from 260.7 to 374.8 mg·g-1 and enhanced the turnover frequency of H2S from 2.50 × 10-4 to 5.35 × 10-4 s-1. The nucleophilic nature of pyridine N enhances the moderate basic sites of the catalyst, enabling the attack of protons and strong H2O dissociation. Moreover, pyridine N also forms cavity sites that anchor CuO, improving Cu dispersion and generating more reactive oxygen species. By providing original insight into the pyridine N-induced bifunctional catalytic removal of COS/H2S in a slightly oxygenated and humid atmosphere, this study offers valuable guidance for further C═S and C-S bond-breaking in the degradation of sulfur-containing pollutants.

Single Droplet Tweezer Revealing the Reaction Mechanism of Mn(II)-Catalyzed SO2 Oxidation.

Sulfate aerosol is one of the major components of secondary fine particulate matter in urban haze that has crucial impacts on the social economy and public health. Among the atmospheric sulfate sources, Mn(II)-catalyzed SO2 oxidation on aerosol surfaces has been regarded as a dominating one. In this work, we measured the reaction kinetics of Mn(II)-catalyzed SO2 oxidation in single droplets using an aerosol optical tweezer. We show that the SO2 oxidation occurs at the Mn(II)-active sites on the aerosol surface, per a piecewise kinetic formulation, one that is characterized by a threshold surface Mn(II) concentration and gaseous SO2 concentration. When the surface Mn(II) concentration is lower than the threshold value, the reaction rate is first order with respect to both Mn(II) and SO2, agreeing with our traditional knowledge. But when surface Mn(II) concentration is above the threshold, the reaction rate becomes independent of Mn(II) concentration, and the reaction order with respect to SO2 becomes greater than unity. The measured reaction rate can serve as a tool to estimate sulfate formation based on field observation, and our established parametrization corrects these calculations. This framework for reaction kinetics and parametrization holds promising potential for generalization to various heterogeneous reaction pathways.

Simultaneously decreasing arsenic and cadmium in rice by soil sulfate and limestone amendment under intermittent flooding.

Water management in paddy soils can effectively reduce the soil-to-rice grain transfer of either As or Cd, but not of both elements simultaneously due to the higher mobility of As under reducing and Cd under oxidizing soil conditions. Limestone amendment, the common form of liming, is well known for decreasing Cd accumulation in rice grown on acidic soils. Sulfate amendment was suggested to effectively decrease As accumulation in rice, especially under intermittent soil flooding. To study the unknown effects of combined sulfate and limestone amendment under intermittent flooding for simultaneously decreasing As and Cd in rice, we performed a pot experiment using an acidic sandy loam paddy soil. We also included a clay loam paddy soil to study the role of soil texture in low-As rice production under intermittent flooding. We found that liming not only decreased rice Cd concentrations but also greatly decreased dimethylarsenate (DMA) accumulation in rice. We hypothesize that this is due to suppressed sulfate reduction, As methylation, and As thiolation by liming in the sulfate-amended soil and a higher share of deprotonated DMA at higher pH which is taken up less readily than protonated DMA. Decreased gene abundance of potential soil sulfate-reducers by liming further supported our hypothesis. Combined sulfate and limestone amendment to the acidic sandy loam soil produced rice with 43% lower inorganic As, 72% lower DMA, and 68% lower Cd compared to the control soil without amendment. A tradeoff between soil aeration and water availability was observed for the clay loam soil, suggesting difficulties to decrease As in rice while avoiding plant water stress under intermittent flooding in fine-textured soils. Our results suggest that combining sulfate amendment, liming, and intermittent flooding can help to secure rice safety when the presence of both As and Cd in coarse-textured soils is of concern.

Sulfur assimilation using gaseous carbonyl sulfide by the soil fungus Trichoderma harzianum.

Fungi have the capacity to assimilate a diverse range of both inorganic and organic sulfur compounds. It has been recognized that all sulfur sources taken up by fungi are in soluble forms. In this study, we present evidence that fungi can utilize gaseous carbonyl sulfide (COS) for the assimilation of a sulfur compound. We found that the filamentous fungus Trichoderma harzianum strain THIF08, which has constitutively high COS-degrading activity, was able to grow with COS as the sole sulfur source. Cultivation with 34S-labeled COS revealed that sulfur atom from COS was incorporated into intracellular metabolites such as glutathione and ergothioneine. COS degradation by strain THIF08, in which as much of the moisture derived from the agar medium as possible was removed, indicated that gaseous COS was taken up directly into the cell. Escherichia coli transformed with a COS hydrolase (COSase) gene, which is clade D of the ß-class carbonic anhydrase subfamily enzyme with high specificity for COS but low activity for CO2 hydration, showed that the COSase is involved in COS assimilation. Comparison of sulfur metabolites of strain THIF08 revealed a higher relative abundance of reduced sulfur compounds under the COS-supplemented condition than the sulfate-supplemented condition, suggesting that sulfur assimilation is more energetically efficient with COS than with sulfate because there is no redox change of sulfur. Phylogenetic analysis of the genes encoding COSase, which are distributed in a wide range of fungal taxa, suggests that the common ancestor of Ascomycota, Basidiomycota, and Mucoromycota acquired COSase at about 790-670 Ma.IMPORTANCEThe biological assimilation of gaseous CO2 and N2 involves essential processes known as carbon fixation and nitrogen fixation, respectively. In this study, we found that the fungus Trichoderma harzianum strain THIF08 can grow with gaseous carbonyl sulfide (COS), the most abundant and ubiquitous gaseous sulfur compound, as a sulfur source. When the fungus grew in these conditions, COS was assimilated into sulfur metabolites, and the key enzyme of this assimilation process is COS hydrolase (COSase), which specifically degrades COS. Moreover, the pathway was more energy efficient than the typical sulfate assimilation pathway. COSase genes are widely distributed in Ascomycota, Basidiomycota, and Mucoromycota and also occur in some Chytridiomycota, indicating that COS assimilation is widespread in fungi. Phylogenetic analysis of these genes revealed that the acquisition of COSase in filamentous fungi was estimated to have occurred at about 790-670 Ma, around the time that filamentous fungi transitioned to a terrestrial environment.

Electrokinetic bioremediation of trichloroethylene and Cr/As co-contaminated soils with elevated sulfate.

Co-contaminants and complex subsurface conditions pose great challenges to site remediation. This study demonstrates the potential of electrokinetic bioremediation (EK-BIO) in treating co-contaminants of chlorinated solvents and heavy metals in low-permeability soils with elevated sulfate. EK-BIO columns were filled with field soils, and were fed by the electrolyte containing 20 mg/L trichloroethylene (TCE), 250 µM Cr(VI), 25 µM As(III), 10 mM lactate, and 10 mM sulfate. A dechlorinating consortium containing Dehalococcoides (Dhc) was injected several times during a 199-d treatment at ∼1 V/cm. Sulfate reduction, Cr/As immobilization, and complete TCE biodechlorination were observed sequentially. EK-BIO facilitated the delivery of lactate, Cr(VI)/As(III), and sulfate to the soils, creating favorable reductive conditions for contaminant removal. Supplementary batch experiments and metagenomic/transcriptomic analysis suggested that sulfate promoted the reductive immobilization of Cr(VI) by generating sulfide species, which subsequently enhanced TCE biodechlorination by alleviating Cr(VI) toxicity. The dechlorinating community displayed a high As(III) tolerance. Metagenomic binning analysis revealed the dechlorinating activity of Dhc and the potential synergistic effects from other bacteria in mitigating heavy metal toxicity. This study justified the feasibility of EK-BIO for co-contaminant treatment and provided mechanistic insights into EK-BIO treatment.

Glycosidase-activated H2S donorsto enhance chemotherapy efficacy.

Hydrogen sulfide (H2S) plays a critical role in cancer biology. Herein, we developed a series of glycosidase-triggered hydrogen sulfide (H2S) donors by connecting sugar moieties (including glucose, galactose and mannose) to COS donors via a self-immolative spacer. In the presence of corresponding glycosidases, H2S was gradually released from these donors in PBS buffer with releasing efficiencies from 36 to 67 %. H2S release was also detected by H2S probe WSP-1 after treatment HepG2 cells with Man1. Cytotoxicities of these glycosylated H2S donors were evaluated against HepG2 by MTT assay. Among them, Man1 and Man2 exhibited an obvious reduction of cell viability in HepG2 cells, with cell viability as 37.6 % for 80 µM of Man. Consistently, significant apoptosis was observed in HepG2 cells after treatment with Man1 and Man2. Finally, We evaluated the potential of Man1 for combination therapy with doxorubicin. A synergistic effect was observed between Man1 and Doxorubicin in HepG2 and Hela cells. All these results indicated glycosidase-activated H2S donorshave promising potential for cancer therapy.

Restricted internal diffusion weakens transpiration-photosynthesis coupling during heatwaves: Evidence from leaf carbonyl sulphide exchange.

Increasingly frequent and intense heatwaves threaten ecosystem health in a warming climate. However, plant responses to heatwaves are poorly understood. A key uncertainty concerns the intensification of transpiration when heatwaves suppress photosynthesis, known as transpiration-photosynthesis decoupling. Field observations of such decoupling are scarce, and the underlying physiological mechanisms remain elusive. Here, we use carbonyl sulphide (COS) as a leaf gas exchange tracer to examine potential mechanisms leading to transpiration-photosynthesis decoupling on a coast live oak in a southern California woodland in spring 2013. We found that heatwaves suppressed both photosynthesis and leaf COS uptake but increased transpiration or sustained it at non-heatwave levels throughout the day. Despite statistically significant decoupling between transpiration and photosynthesis, stomatal sensitivity to environmental factors did not change during heatwaves. Instead, midday photosynthesis during heatwaves was restricted by internal diffusion, as indicated by the lower internal conductance to COS. Thus, increased evaporative demand and nonstomatal limitation to photosynthesis act jointly to decouple transpiration from photosynthesis without altering stomatal sensitivity. Decoupling offered limited potential cooling benefits, questioning its effectiveness for leaf thermoregulation in xeric ecosystems. We suggest that adding COS to leaf and ecosystem flux measurements helps elucidate diverse physiological mechanisms underlying transpiration-photosynthesis decoupling.

Catalytic co-combustion of biomass and brown coal in a fluidized bed: Economic and environmental benefits.

The work is devoted to the study of combustion of brown coal, pine sawdust, and their mixtures in a fluidized bed of catalyst at 600-750°Ð¡. It is shown that an increase in the content of sawdust in a mixture with brown coal leads to an increase in the burnout degree of solid fuel from 94.4% to 99.9%, while the emission of greenhouse gases in the form of CO2 CO and NOx is reduced (CO2 from the biomass is not included in the balance). The high content of alkaline earth metal oxides (CaO and MgO) in the mineral part of brown coal, sawdust, and their mixtures eliminates the emission of sulfur oxides and the slagging of heat-exchange surfaces during the combustion in a fluidized bed of catalyst. The optimal temperature, when the highest burnout degree of the above fuels is achieved in the combustion is 750°Ð¡. It is also shown that the increase in temperature and the content of sawdust in the composition of the fuel mixtures has a positive effect on the economic and environmental process indicators.

Effects of emission control areas on sulfur-oxides concentrations--Evidence from the coastal ports in China.

The setting of Sulfur limitations in Emission Control Areas (ECAs) is a crucial action of marine environmental governance at the international regulatory levels. In this study, the overall and structural impacts of the two rounds of ECA policies on SOx concentrations were quantified using synthetic control method (SCM) based on time-series data from Chinese coastal ports from 2005 to 2020. From the outcomes, the 1st round of ECA policy announced in 2015 intensified the competition between ECA and non-ECA ports and provided strong support for ECA expansion and enhanced regulation in 2019. In addition, the restrictions on the Sulfur content of marine fuels under the 1st round of ECA policy has only effectively reduced the SOx concentration in the Bohai Rim and the Yangtze River Delta region, whereas the impact on the Pearl River Delta region isn't significant. However, the 2nd round of ECA policy has only effectively impacted the Bohai Rim. In general, the effect of the 1st round of ECA policy is better than that of the 2nd round, which is mainly because the favorable effect of the further expansion of ECA policy is offset by a significant increase in vessel activity in Chinese coastal ports.

Differential evaluation of sulfur oxides in the natural lake water samples by carbazole-furan fluorescent probe.

Water bodies are frequently polluted, with sulfur oxides being the most common form of water pollution. Therefore, developing a detection mechanism for sulfur oxides in water bodies is particularly urgent. A new fluorescent probe YX-KZBD was designed and developed. This probe releases fluorescent signals with its own sulfurous acid recognition site, detects sulfurous acid based on the Michael addition reaction, and evaluates the pollution degree of sulfur oxides in the water environment through the transformation mode of the sulfur cycle. This probe has high energy transfer efficiency in aqueous solutions. In addition, the fluorescence data obtained by analyzing the water samples were linearly fitted with the gene abundance values of the functional genes of sulfur-producing bacteria, and a significant correlation was obtained. The Kriging interpolation model was used to evaluate the sulfate content distribution at each sampling point to understand the distribution of sulfur oxides in natural water intuitively. The fluorescence signal excited by the probe was also combined with a real-time quantitative polymerase chain reaction (qPCR), and sulfate-reducing and sulfur-oxidizing bacteria were introduced in the sulfur cycle, providing a new method to assess the extent of water pollution effectively.

Effects of operating conditions on the in situ control of sulfur-containing odors by using a novel alternative landfill cover and its transformation mechanism.

Sulfur-containing gases are main sources of landfill odors, which has become a big issue for pollution to environment and human health. Biocover is promising for treating landfill odors, with advantages of durability and environmental friendliness. In this study, charcoal sludge compost was utilized as the main effective component of a novel alternative landfill cover and the in situ control of sulfur-containing odors from municipal solid waste landfilling process was simulated under nine different operating conditions. Results showed that five sulfur-containing odors (hydrogen sulfide, H2S; methyl mercaptan, CH3SH; dimethyl sulfide, CH3SCH3; ethylmercaptan, CH3CH2SH; carbon disulfide, CS2) were monitored and removed by the biocover, with the highest removal efficiencies of 77.18% for H2S, 87.36% for CH3SH, and 92.19% for CH3SCH3 in reactor 8#, and 95.94% for CH3CH2SH and 94.44% for CS2 in reactor 3#. The orthogonal experiment showed that the factors influencing the removal efficiencies of sulfur-containing odors were ranked from high to low as follows: temperature > weight ratio > humidity content. The combination of parameters of 20% weight ratio, 25°C temperature, and 30% water content was more recommended based on the consideration of the removal efficiencies and economic benefits. The mechanisms of sulfur conversion inside biocover were analyzed. Most organic sulfur was firstly degraded to reduced sulfides or element sulfur, and then oxidized to sulfate which could be stable in the layer as the final state. In this process, sulfur-oxidizing bacteria play a great role, and the distribution of them in reactor 1#, 5#, and 8# was specifically monitored. Bradyrhizobiaceae and Rhodospirillaceae were the dominant species which can utilize sulfide as substance to produce sulfate and element sulfur, respectively. Based on the results of OUTs, the biodiversity of these sulfur-oxidizing bacteria, these microorganisms, was demonstrated to be affected by the different parameters. These results indicate that the novel alternative landfill cover modified with bamboo charcoal compost is effective in removing sulfur odors from landfills. Meanwhile, the findings have direct implications for addressing landfill odor problems through parameter adjustment.

Elucidating the Mechanism on the Transition-Metal Ion-Synergetic-Catalyzed Oxidation of SO2 with Implications for Sulfate Formation in Beijing Haze.

Currently, atmospheric sulfate aerosols cannot be predicted reliably by numerical models because the pathways and kinetics of sulfate formation are unclear. Here, we systematically investigated the synergetic catalyzing role of transition-metal ions (TMIs, Fe3+/Mn2+) in the oxidation of SO2 by O2 on aerosols using chamber experiments. Our results showed that the synergetic effect of TMIs is critically dependent on aerosol pH due to the solubility of Fe(III) species sensitive to the aqueous phase acidity, which is effective only under pH < 3 conditions. The sulfate formation rate on aerosols is 2 orders of magnitude larger than that in bulk solution and increases significantly on smaller aerosols, suggesting that such a synergetic-catalyzed oxidation occurs on the aerosol surface. The kinetic reaction rate can be described as R = k*[H+]-2.95[Mn(II)][Fe(III)][S(IV)] (pH ≤ 3.0). We found that TMI-synergetic-catalyzed oxidation is the dominant pathway of sulfate formation in Beijing when haze particles are very acidic, while heterogeneous oxidation of SO2 by NO2 is the most important pathway when haze particles are weakly acidic. Our work for the first time clarified the role and kinetics of TMI-synergetic-catalyzed oxidation of SO2 by O2 in haze periods, which can be parameterized into models for future studies of sulfate formation.

Autotrophic degradation of sulfamethoxazole using sulfate-reducing biocathode in microbial photo-electrolysis system.

Sulfamethoxazole is a representative of sulfonamide antibiotic pollutants. This study aims to investigate the degradation pathways of sulfamethoxazole and the response of microbial communities using the autotrophic biocathode in microbial photo-electrolysis systems (MPESs). Sulfamethoxazole with an initial concentration of 2 mg L-1 was degraded into small molecule propanol within 6 h with the biocathode. Elemental sulfur (S0) was detected in the cathode chamber, accounting for 57 % of the removed sulfate. The conversion from sulfate to S0 indicated that autotrophic microorganisms might adopt a novel pathway for sulfamethoxazole removal in the MPES. In the abiotic cathode, sulfamethoxazole degradation rate was 0.09 mg L-1 h-1 with the electrochemistry process. However, sulfamethoxazole was converted to products that still contain benzene rings, including p-aminothiophenol, 3-amino-5-methylisoxazole, and sulfonamide. The microbial community analysis indicated that the synergistic interaction of Desulfovibrio and Acetobacterium promoted the autotrophic degradation of sulfamethoxazole. The results suggested that autotrophic microorganisms may play an important role in the environmental transformation of sulfamethoxazole.

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.

Degradation of algae promotes the release of arsenic from sediments under high-sulfate conditions.

Sulfate concentrations in eutrophic waters continue to increase; however, the transformations of arsenic (As) in sediments under these conditions are unclear. In this study, we constructed a series of microcosms to investigate the effect of algal degradation on As transformations in sediments with high sulfate concentrations. The results showed that both the elevated sulfate levels and algal degradation enhanced the release of As from sediments to the overlying water, and degradation of algal in the presence of elevated sulfate levels could further contribute to As release. Sulfate competed with arsenate for adsorption in the sediments, leading to As desorption, while algal degradation created a strongly anaerobic environment, leading to the loss of the redox layer in the surface sediments. With high sulfate, algal degradation enhanced sulfate reduction, and sulfur caused the formation of thioarsenates, which may cause re-dissolution of the arsenides, enhancing As mobility by changing the As speciation. The results of sedimentary As speciation analysis indicated that elevated sulfur levels and algal degradation led to a shift of As from Fe2O3/oxyhydroxide-bound state to specifically adsorbed state at the sediment water interface. This study indicated that algal degradation increases the risk of As pollution in sulfate-enriched eutrophic waters.