Potential Electron Acceptors Research Articles

Specific interaction of resorufin to outer-membrane cytochrome OmcE of Geobacter sulfurreducens: A new insight on artificial electron mediators in promoting extracellular electron transfer

Bioelectrochemical system (BES) is a unique biotechnology for wastewater treatment and energy recovery, and extracellular electron transfer (EET) between microbe and electrode is the key to optimize the performance of BESs. Resazurin is an effective artificial compound that can promote EET in BESs, but the way how it transports electrons is not fully understood. In this study differential pulse voltammetry revealed that the redox potential of resorufin (RR) (intermediate of resazurin reduction, actual electron mediator) within Geobacter sulfurreducens biofilm was positively shifted by 100 mV than that of free RR, and this shift was attenuated by the mutation of outer-membrane cytochrome gene omcE but not by omcS and omcZ mutation, indicating that RR specifically interacted with OmcE. By using heterologously expressed OmcE monomers in Escherichia coli, it was found that RR bonded with OmcE monomers with a moderate intensity (dissociation constant of 720 nM), and their interaction obviously increased the content of α helix in OmcE monomers. Biomolecular analysis indicated that heme II of OmcE monomer might be the binding site for RR (binding energy of -7.01 kJ/mol), which were favorable for electron transfer within OmcE-RR complex. Comparative transcriptomics showed that RZ addition significantly upregulated the expression of omcE, periplasmic cytochrome gene ppcB, and outer-membrane genes omaB, ombB and omcB, thus, it was hypothesized that OmcE-bound RR might serve as potential electron acceptor of OmbB-OmaB-OmcB porin complex which passes electrons across outer membrane. Our work demonstrated a new pathway of artificial electron mediators in facilitating EET in Geobacter species, which may guide the application of electron mediator in improving the performance of BESs.

Determining the binding mechanism of B12N12(Zn) with CH4, CO, CO2, H2O, N2, NH3, NO, NO2, O2, and SO2 gases

In this study, an exploration of molecular interactions between CH4, CO, CO2, H2O, N2, NH3, NO, NO2, O2, SO2 gas molecules and B12N12(Zn) nanocage is conducted using advanced computational techniques, ωB97XD/Def2tzvp, unraveling fundamental behaviors. Employing global optimization methods and sophisticated tools like the bee colony algorithm in ABCluster software, the research offers insights into energy adsorption processes, confirming molecular stability through DFT calculations. The determination of electrophilicity index values through conceptual DFT analysis sheds light on relative reactivity levels and charge transfer phenomena, emphasizing that in some cases the nanocage's role as a potential electron acceptor. Natural bond analysis of charge transfer direction and valence shell orbital interactions enriches understanding, supported by comprehensive parameter compilation and critical point visualization. Further confirmation of interaction types and strengths through G(r)/V(r) ratios and ELF values enhances comprehension through quantum theory of atoms in molecule analysis. Ultimately, this study contributes significantly to computational chemistry, laying foundations for molecular design and engineering advancements. It sets the stage for future progress in materials science and catalysis, promising innovation in sustainable energy solutions and technological development.

Artificial electron snorkels reduce CH4 emissions in paddy soil: Regulation of the electron transfer pathway and microbial community ecology

Climate science has focused on reducing emissions of atmospheric CH4 from paddy soils, as CH4 has stronger infrared absorption characteristics than CO2. Like cable bacteria, artificial electron snorkels (made of solid graphite rods) have been proposed in this study to provide potential remote electron acceptors for soil anaerobic metabolism to compete with methanogenic processes. A systematic investigation was conducted on the modulation of the CH4 emission dynamics by electron snorkels at different densities, as well as the associated metabolism of C/N/Fe in paddy soil. During 124 days of operation, the electron snorkels suppressed CH4 emissions by 7–31% over ten sampling periods, and the high-density setting exhibited stronger performance. The electron snorkels accelerated the early mineralization of soil organic matter, increasing the content of dissolved organic matter by 20–236%. These organics were utilized by microorganisms, where O2, NO3−, and Fe3+ acted as electron acceptors, enhancing soil alternative respiration and producing CO2. Metagenomic and 16S rRNA gene sequencing revealed that microbial abundance and diversity were increased by 4–71% in the soil bottom layer (7 cm–8 cm depth) driven by electron snorkels. Moreover, electron snorkels potentially prevented CH4 escape by either improving soil permeability or electrically stimulating the abundance of methanotrophs (e.g., Methylocystis). The ratio of methanogenic to methane-oxidizing gene abundances was reduced by 22–66% under the electron snorkels. Our results indicate that the applied electron snorkels have significant potential in enriching the soil microbial community involved in methane cycling to mitigate CH4 emissions from paddy fields.

Hydrogen peroxide production in pure water on a pyrrole-containing hydrothermal carbon photocatalyst

Herein, a pyrrole-containing hydrothermal carbon (N-SHTC) was developed by a simple one-step hydrothermal carbonization approach using starch and nitric acid as starting reactants. The introduction of nitric acid promoted the dehydration and carbonization of starch and led to the synthesis of N-SHTC at lower hydrothermal temperature, and also resulted in the incorporation of N into the furan structure to form pyrrole units. The charge transfer efficiency of N-SHTC was significantly improved due to the introduced pyrrole units as potential electron acceptor. With no scavengers or O2 bubbling, N-SHTC exhibited a H2O2 production rate of 1132 μmol g−1 h−1 in pure water under visible light. Notably, the H2O2 photoproduction performance of N-SHTC was further enhanced in the presence of metal salt ions due to the strengthened electron-withdrawing property of pyrrole units caused by the metal salt ions. These merits enabled N-SHTC the potentially practical applications in photocatalytic production of H2O2.

Temperature, pH, and oxygen availability contributed to the functional differentiation of ancient Nitrososphaeria.

Ammonia-oxidizing Nitrososphaeria are among the most abundant archaea on Earth and have profound impacts on the biogeochemical cycles of carbon and nitrogen. In contrast to these well-studied ammonia-oxidizing archaea (AOA), deep-branching non-AOA within this class remain poorly characterized because of a low number of genome representatives. Here, we reconstructed 128 Nitrososphaeria metagenome-assembled genomes from acid mine drainage and hot spring sediment metagenomes. Comparative genomics revealed that extant non-AOA are functionally diverse, with capacity for carbon fixation, carbon monoxide oxidation, methanogenesis, and respiratory pathways including oxygen, nitrate, sulfur, or sulfate, as potential terminal electron acceptors. Despite their diverse anaerobic pathways, evolutionary history inference suggested that the common ancestor of Nitrososphaeria was likely an aerobic thermophile. We further surmise that the functional differentiation of Nitrososphaeria was primarily shaped by oxygen, pH, and temperature, with the acquisition of pathways for carbon, nitrogen, and sulfur metabolism. Our study provides a more holistic and less biased understanding of the diversity, ecology, and deep evolution of the globally abundant Nitrososphaeria.

Intermediates Production in Methane Oxidation Coupled with Denitrification: Current Status, Challenges, and Future Opportunities

Climate warming is a hot environmental issue of global concern. As one of the major methane sinks, the process of methane oxidation coupled with denitrification (MOD) reduces the environmental impact brought by the greenhouse effect and water eutrophication. In addition, as an energy substance, methane can also improve its economic value by transforming into other liquid chemicals. Previous studies on the mechanism of the process have mainly focused on the extracellular electron transfer between species. However, in recent years, the production of intermediates influenced by different factors, and the existence of a large number of acid-producing bacteria and methanogens under anaerobic conditions, has led some researchers to pursue research into a new mechanism of the process. Moreover, the discovery of CO2 as a potential electron acceptor in products is certainly exciting, being a big opportunity under the ‘carbon neutral’ policy. This review looks back at the development of the MOD process and describes its functional microorganism and mechanism in detail when summarizing the types of microorganisms and intermediates at different oxygen levels, and introduces some traditional and novel biotechnologies, such as metagenomics, meta-transcriptomics, and meta-proteomics, etc., to help explore the novel mechanism of the process of MOD mediated by intermediates.

Exploring substrate interaction in respiratory alternative complex III from Rhodothermus marinus

Rhodothermus marinus is a thermohalophilic organism that has optimized its microaerobic metabolism at 65 °C. We have been exploring its respiratory chain and observed the existence of a quinone:cytochrome c oxidoreductase complex, named Alternative Complex III, structurally different from the bc1 complex. In the present work, we took profit from nanodiscs and liposomes technology to investigate ACIII activity in membrane-mimicking systems. In addition, we studied the interaction of ACIII with menaquinone, its potential electron acceptors (HiPIP and cytochrome c) and the caa3 oxygen reductase.

Design, synthesis, and electroluminescence of red TADF dyes based on cyanophenanthrene

Two rigid electron-deficient cyanophenanthrene frameworks with limited π-conjugation, phenanthrene-9-carbonitrile (CNP) and phenanthrene-9,10-dicarbonitrile (DCNP), are employed as the electron acceptors to construct thermally activated delayed fluorescence (TADF) dyes. The new TADF emitters exhibit long-wavelength emission without strong long-range π-π stacking or interchromophore coupling, as supported by the photophysical and crystallographic results. These unique features are suitable to construct red organic light-emitting diodes (OLEDs). An OLED based on CNP-TPXZ showed an orange-red emission with a peak at 586 nm and a maximum EQE of 8.4%, while that of DCNP-DPXZ exhibited red emission at 614 and a maximum EQE of 6.6%. These results demonstrate that DCNP and CNP are potential electron acceptors for the development of red TADF emitters and OLEDs.

Coupled reduction of structural Fe(III) in nontronite and oxidation of petroleum hydrocarbons

Fe-bearing clay minerals are frequently present in oil reservoirs as potential electron acceptor. Compounds in crude oil may mediate microbial reduction of structural Fe(III) in clay minerals through their roles as electron donor and shuttle. However, there is limited knowledge about these roles and resulting transformation of oil compounds. In this study, bio-reduction of structural Fe(III) in nontronite (NAu-2, Fe-rich smectite) by the dissimilatory iron-reducing bacterium (DIRB) Shewanella putrefaciens CN32 was investigated in the presence of either crude oil or specific fractions of oil. Lactate was added in some experiments as extra electron donor. The fractions of saturates (nC14-nC20 alkanes and nC8-nC14-alkyl cyclohexanes), aromatics (with two/three benzene rings), and polar compounds (carboxylic acids) of crude oil were adsorbed to NAu-2 surface. Without CN32, crude oil was able to slightly reduce structural Fe(III) in NAu-2. In the presence of CN32, reduction of Fe(III) in NAu-2 was coupled with oxidation of bulk oil and saturated/aromatic fractions. The reduction extent (21.5 ± 0.3%) and rate (0.04 ± 0.00 mM/h) by the saturated oil fraction (nC17-nC30 alkanes and nC10-nC23-alkyl cyclohexanes as electron donors) were slightly lower than those by bulk oil (22.8 ± 0.4% and 0.05 ± 0.00 mM/h, respectively), but those by the aromatic fraction with two benzene rings were much higher (30.8 ± 0.2% and 0.15 ± 0.00 mM/h, respectively). Fe(III) bio-reduction was coupled with oxidative transformation of oil compounds. Specifically, n-alkanes and alkyl cyclohexanes with shorter carbon chains and aromatic isomers with fewer methyl groups were more easily degraded (i.e., dibenzothiophene series) and/or desorbed (i.e., phenanthrene series) than n-alkanes and alkyl cyclohexanes with longer carbon chains and aromatic isomers with more methyl groups. These hydrocarbons were degraded to oxygen-containing compounds, mainly saturated fatty acids, monocyclic naphthenic acids, and phenols. In the presence of lactate as extra electron donor, the aromatic fraction significantly promoted the Fe(III) bio-reduction extent and rate, suggesting its role as electron shuttle. The oxidative transformation of oil compounds driven by bio-reduction of clay minerals has broad implications for the coupled biogeochemical cycles of carbon and iron in oil reservoirs and organic-rich sedimentary rocks.

Single Amino Acid Residues Control Potential‐Dependent Inactivation of an Inner Membrane bc‐Cytochrome**

AbstractDuring extracellular electron transfer, Geobacter sulfurreducens constitutively expresses the bc‐cytochrome CbcL, yet cells containing only this menaquinone oxidase fail to respire above −0.1 V vs. SHE. By identifying mutations within cbcL that permit growth at higher potentials, we provide evidence that this cytochrome is regulated by redox potential. Strains expressing only CbcLV205A, CbcLV205G, and CbcLF525Y were capable of growth with high potential electron acceptors including Fe(III) citrate, Mn(IV) oxides, and electrodes poised at +0.1 V vs. SHE. Electrochemical characterization of wild type CbcL revealed oxidative inactivation of electron transfer above −0.1 V, while CbcLV205A, CbcLV205G, and CbcLF525Y remained active. Growth yields of CbcLV205A, CbcLV205G, and CbcLF525Y were only 50 % of WT, consistent with CbcL‐dependent electron transfer conserving less energy. These data support the hypothesis that CbcL has evolved to rapidly shut off in response to redox potential, in order to divert electrons to higher yield oxidases that coexist in the Geobacter membrane.

Ultrafast Electron Transfer in Au–Cyanobacteria Hybrid for Solar to Chemical Production

The rise of inorganic–biohybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic–abiotic interface to drive the development of next-generation hybrid systems. The model system, cyanobacteria–gold nanoparticle hybrids, combines a light harvester with a photosynthetic bacterium to drive the reduction of CO2 to glycerol with improved efficiency and increased glycerol production by 14.6%, in comparison to cyanobacteria only. In this work, we report insights into this unique photochemical behavior and propose a charge-transfer pathway from Au nanoparticle to cyanobacteria. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates are on the order of a few ps to the potential electron acceptor in photosystem II. This work represents a promising platform to utilize a conventional spectroscopic methodology to extract insights from more complex biotic–abiotic hybrid systems.

Evaluating the efficacy of slow-releasing carbon source tablets for in situ biological heterotrophic denitrification of groundwater.

Slow-releasing precipitating tablets (SRPTs) and slow-releasing floating tablets (SRFTs) were formulated to release fumarate as a carbon source (CS) and/or electron donor (ED) in an in situ biological heterotrophic denitrification system. These tablets were prepared using pharmaceutical manufacturing. Soil column tests were conducted to evaluate nitrate denitrification efficacy, microbial population changes, and mass balance of fumarate and potential electron acceptors. Significant and simultaneous consumption of both fumarate and nitrate, and the production and consumption of nitrite were observed in both SRPT-treated and SRFT-treated soil columns. These results suggest that SRPT and SRFT releasing fumarate, induce heterotrophic biological denitrification. In the SRPT- and SRFT-treated columns, 65% and 73% of fumarate were associated with heterotrophic denitrification, respectively. Particularly, surplus citric acid, originally designed to serve as a floating agent, was utilized for 36% and 28% for SRFT flotation and denitrification, respectively. The results of 16s RNA analyses revealed that a bacterium that shared 99% 16s rRNA sequence similarity with those of Azoarcus sp. AN9, and Pseudogulbenkiania sp. NH8B, a facultative heterotrophic denitrifier, was detected in the column effluent. This study confirms that SRPT and SRFT can effectively operate long-term in situ biological denitrification processes, because it is possible to supply detailed CS and/or ED uniformly by applying both SRPT and SRFT in the well.

Electron acceptors determine the BTEX degradation capacity of anaerobic microbiota via regulating the microbial community

Anaerobic degradation is the major pathway for microbial degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) under electron acceptor lacking conditions. However, how exogenous electron acceptors modulate BTEX degradation through shaping the microbial community structure remains poorly understood. Here, we investigated the effect of various exogenous electron acceptors on BTEX degradation as well as methane production in anaerobic microbiota, which were enriched from the same contaminated soil. It was found that the BTEX degradation capacities of the anaerobic microbiota gradually increased along with the increasing redox potentials of the exogenous electron acceptors supplemented (WE: Without exogenous electron acceptors < SS: Sulfate supplement < FS: Ferric iron supplement < NS: Nitrate supplement), while the complexity of the co-occurring networks (e.g., avgK and links) of the microbiota gradually decreased, showing that microbiota supplemented with higher redox potential electron acceptors were less dependent on the formation of complex microbial interactions to perform BTEX degradation. Microbiota NS showed the highest degrading capacity and the broadest substrate-spectrum for BTEX, and it could metabolize BTEX through multiple modules which not only contained fewer species but also different key microbial taxa (eg. Petrimonas, Achromobacter and Comamonas). Microbiota WE and FS, with the highest methanogenic capacities, shared common core species such as Sedimentibacter, Acetobacterium, Methanobacterium and Smithella/Syntrophus, which cooperated with Geobacter (microbiota WE) or Desulfoprunum (microbiota FS) to perform BTEX degradation and methane production. This study demonstrates that electron acceptors may alter microbial function by reshaping microbial community structure and regulating microbial interactions and provides guidelines for electron acceptor selection for bioremediation of aromatic pollutant-contaminated anaerobic sites.

Investigating the Role of Novel Benzotrithiophene-Based Bat-Shaped Non-Fullerene Acceptors for High Performance Organic Solar Cells

The development of an effective building blocks considered the boon in constructing highly efficient nonfullerene electron acceptors (NFEAs). The first theoretical design and investigation of environmental-friendly groups for changing potential end-capped electron acceptor molecules for high-performance environmental-friendly OSCs is proposed in this study. We developed BTT-based [Formula: see text]–[Formula: see text]–[Formula: see text]–[Formula: see text]–[Formula: see text] (acceptor–bridge–core–bridge–acceptor) type, neoteric Bat-shaped environmental-friendly acceptor molecules (K1–K6) for the first time by replacing the electronegative –F group of BTT with four electron-withdrawing (–CN, –COOCH3, –NO2, –Cl) groups. K1–K6 has its exciton-binding energy ([Formula: see text]), open-circuit voltage ([Formula: see text]), frontier molecular orbital analysis (FMO), transition density matrix (TDM) analysis, electron and hole reorganization energy ([Formula: see text]e, [Formula: see text]h), density of state (DOS) graphs, and transition energy Ex values computed and compared to the recently proposed high-performance BTT molecule. According to the research, the photovoltaic, photo-physical and electrical applications of proposed molecules K1–K6 are comparable to those of [Formula: see text]. When compared to reference [Formula: see text] and proposed molecules, K6 tested to be the proverbial optoelectronic compound for OSCs due to its low [Formula: see text] (2.05[Formula: see text]eV), lowest [Formula: see text] (1.57[Formula: see text]eV), highest [Formula: see text] max values of 790.61[Formula: see text]nm in CHCl3, 0.95[Formula: see text]V value for [Formula: see text] and comparable [Formula: see text] (0.482[Formula: see text]eV). The superposition of orbitals and lucrative charge shift from the highest occupied molecular orbital (HOMO) (PTB7-Th) to the lowest unoccupied molecular orbital (LUMO) were verified by charge transfer study among the K6: PTB7-Th combine. As a result, the proposed molecules (K1–K6) with exceptional optoelectronic capabilities are suggested as the best harmless alternative materials for creating proficient and environmental-friendly OSCs.

Methanogenesis from Mineral Carbonates, a Potential Indicator for Life on Mars

Priorities for the exploration of Mars involve the identification and observation of biosignatures that indicate the existence of life on the planet. The atmosphere and composition of the sediments on Mars suggest suitability for anaerobic chemolithotrophic metabolism. Carbonates are often considered as morphological biosignatures, such as stromatolites, but have not been considered as potential electron acceptors. Within the present study, hydrogenotrophic methanogen enrichments were generated from sediments that had received significant quantities of lime from industrial processes (lime kiln/steel production). These enrichments were then supplemented with calcium carbonate powder or marble chips as a sole source of carbon. These microcosms saw a release of inorganic carbon into the liquid phase, which was subsequently removed, resulting in the generation of methane, with 0.37 ± 0.09 mmoles of methane observed in the steel sediment enrichments supplemented with calcium carbonate powder. The steel sediment microcosms and lime sediments with carbonate powder enrichments were dominated by Methanobacterium sp., whilst the lime/marble enrichments were more diverse, containing varying proportions of Methanomassiliicoccus, Methanoculleus and Methanosarcina sp. In all microcosm experiments, acetic acid was detected in the liquid phase. Our results indicate that chemolithotrophic methanogenesis should be considered when determining biosignatures for life on Mars.

Structural Features of Cytochrome b5-Cytochrome b5 Reductase Complex Formation and Implications for the Intramolecular Dynamics of Cytochrome b5 Reductase.

Membrane cytochrome b5 reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b5, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b5 reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b5 reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b5 and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.

Sulfate‐ and iron‐dependent anaerobic methane oxidation occurring side‐by‐side in freshwater lake sediment

AbstractAnaerobic oxidation of methane (AOM) is a potentially important methane sink in lake sediments, but the biogeochemistry and microbial ecology of this process are understudied. Potential electron acceptors for AOM include Fe(III) and sulfate; however, it is not clear to which extent low sulfate concentrations constrain the coupling of AOM to sulfate reduction, nor if Fe(III) reduction drives AOM directly or via a cryptic sulfur cycle. We investigated AOM pathways in the sediment of iron‐rich Danish Lake Ørn through anoxic sediment slurry incubations with additions of 13C‐labeled methane as a substrate, sulfate and Fe(III) as potential electron acceptors, and molybdate as an inhibitor of sulfate reduction. The experiments demonstrated the co‐occurrence of sulfate‐ and iron‐dependent modes of AOM, with the former supported by recycling of sulfate coupled to iron reduction. Quantitative PCR analysis demonstrated the abundance of archaea of the ANME‐2d clade (Ca. Methanoperedenaceae) as likely drivers of AOM. Our study demonstrates that sulfate‐dependent AOM can consume methane at sulfate concentrations typical for freshwater systems and emphasizes the importance of sulfur and iron cycling in the regulation of methane emission from freshwater sediments.

Nitrate-dependent anaerobic methane oxidation and chemolithotrophic denitrification in a temperate eutrophic lake.

While the emissions of methane (CH4) by natural systems have been widely investigated, CH4 aquatic sinks are still poorly constrained. Here, we investigated the CH4 cycle and its interactions with nitrogen (N), iron (Fe) and manganese (Mn) cycles in the oxic-anoxic interface and deep anoxic waters of a small, meromictic and eutrophic lake, during two summertime sampling campaigns. Anaerobic CH4 oxidation (AOM) was measured from the temporal decrease of CH4 concentrations, with the addition of three potential electron acceptors (NO3-, iron oxides (Fe(OH)3) and manganese oxides (MnO2)). Experiments with the addition of either 15N-labeled nitrate (15N-NO3-) or 15N-NO3- combined with sulfide (H2S), to measure denitrification, chemolithotrophic denitrification and anaerobic ammonium oxidation (anammox) rates, were also performed. Measurements showed AOM rates up to 3.8µmol CH4 L-1 d-1 that strongly increased with the addition of NO3- and moderately increased with the addition of Fe(OH)3. No stimulation was observed with MnO2 added. Potential denitrification and anammox rates up to 63 and 0.27µmol N2 L-1 d-1, respectively, were measured when only 15N-NO3- was added. When H2S was added, both denitrification and anammox rates increased. Altogether, these results suggest that prokaryote communities in the redoxcline are able to efficiently use the most available substrates.

Biogeochemical influences on net methylmercury formation proxies along a peatland chronosequence

A geographically constrained chronosequence of peatlands divided into three age classes (young, intermediate and old) was used to explore the role of biogeochemical influences, including electron donors and acceptors as well as chemical speciation of inorganic mercury (Hg(II)), on net formation of methylmercury (MeHg) as approximated by the fraction of MeHg to total mercury (THg) in the peat soil. We hypothesized that removing vascular plants would reduce availability of electron donors and thus net MeHg formation. However, we found no effect of the vascular plant removal. The sum of the potential electron donors (acetate, lactate, propionate and oxalate), the electron donation proxy organic C/Organic N, and the potential electron acceptors (Fe(III), Mn and sulfate) in porewater all showed significant correlations with the net MeHg formation proxies in peat soil (MeHg concentration and %MeHg of THg). Thus differences in both electron donor and acceptor availability may be contributing to the pattern of net MeHg formation along the chronosequence. In contrast, Hg(II) concentrations in peat porewater showed small differences along the gradient. A chemical speciation model successfully predicted the solubility of Hg and MeHg in the porewater. The modeling pointed to an enhanced concentration of Hg-polysulfide species in the younger peatlands as a potential factor behind increased Hg(II) solubility and methylation in the more nutrient-rich peatlands. This work contributes to the understanding of Hg and MeHg cycling in peatlands which can help guide mitigation measures to reduce aquatic MeHg biomagnification in peatland dominated landscapes.

Unraveling nitrogen removal and microbial response of marine anammox bacteria-dominated consortia to Mo(VI) addition in nitrogen-laden saline wastewater treatment

Enhanced performance of anammox process has attracted public attention in treating saline wastewater with marine anammox bacteria. The addition of some key metal elements would enhance metabolic activity in wastewater treatment. Herein, responses of marine anammox bacteria (MAB) to Mo(VI) addition were explored in nitrogen-laden saline wastewater treatment. The experiment was conducted at a low temperature (15 ± 1 °C). With the optimal Mo(VI) concentration of 2.1 mg/(g VSS), the substrate removal rate reached the maximum of 1.41 kg N/(m3·d). Specific anammox activity and substrate conversion rate increased by 16.0% and 36.9%, respectively. The lower ΔNO2--N/ΔNH4+-N indicated the presence of the potential electron acceptor. Moreover, the relative abundance of Cadidatus Scalindua increased by 4.18% during this experiment. Dynamic analysis showed that the remodified Logistic model was proper to analyze nitrogen removal with Mo(VI) addition. An appropriate Mo(VI) dosage (0.5–4 mg/L) would shorten the lag time of anammox process greatly.