Isotope Tracer Experiments Research Articles

Boosting electrosynthesis of urea from N2 and CO2 by defective Cu-Bi

Electrosynthesis of urea from N2 and CO2 molecules is of immense significance but has so far been plagued by the lack of a universal design principle to guide the search for new catalysts. Herein, as exemplified by the Cu-Bi catalyst, our findings revealed that the defective Cu-Bi catalyst could offer a maximum urea concentration of 0.45 ± 0.06 mg L−1 and the largest faradaic efficiency of 8.7% ± 1.7% at −0.4 V (versus reversible hydrogen electrode [RHE]), exhibiting outstanding activity in contrast to monometallic (Cu and Bi) and bimetallic (Cu-Bi mixture and intact Cu-Bi) catalysts. Moreover, the evidence from isotope tracing experiments, in situ Raman spectroscopy, and density functional theory (DFT) calculations suggested that it is a promising strategy for the co-reduction of N2 and CO2 by defective Cu-Bi catalysts, switching on a light to the application of defects in electrosynthesis of urea.

Rates and physicochemical drivers of microbial anabolic activity in deep-sea sediments and implications for deep time.

Sediment microorganisms influence global climate and redox by altering rates of organic carbon burial. However, the activity and ecology of benthic microorganisms are poorly characterized, especially in the deep sea. Here, we conducted nearly 300 stable isotope tracer experiments in sediments from the Pacific and Atlantic oceans (100-4500 m water depth) to determine the rates, spatial distribution, and physicochemical controls on microbial total anabolic activity, nitrogen fixation, and inorganic/organic carbon uptake. Using correlative and manipulative approaches, we find that total activity is limited primarily by organic carbon and/or energy. Activity correlates significantly with distance from shore, sediment depth, C:N ratios, and overlying chlorophyll concentrations and is stimulated by carbon but not nitrogen additions. Consistent with this, nitrogen fixation was undetected despite relatively low concentrations of porewater ammonium and the previous detection of nifH genes. Inorganic carbon uptake accounted for 7%-55% of carbon assimilation per sample (median 21%), suggesting chemoautotrophy is an important and unappreciated source of labile carbon in deep-sea sediments. Community 16S rRNA was dominated by Bacteria (<2% Archaea), primarily Desulfobacterales of the Deltaproteobacteria. Leveraging our findings, we modelled global benthic microbial activity through geologic time and find the potential for significant shifts in total activity with supercontinental cycles.

Insect Gut Isolate Pseudomonas sp. Strain Nvir Degrades the Toxic Plant Metabolite Nitropropionic Acid.

ABSTRACTNitropropionic acid (NPA) is a widely distributed naturally occurring nitroaliphatic toxin produced by leguminous plants and fungi. The Southern green shield bug feeds on leguminous plants and shows no symptoms of intoxication. Likewise, its gut-associated microorganisms are subjected to high levels of this toxic compound. In this study, we isolated a bacterium from this insect's gut system, classified as Pseudomonas sp. strain Nvir, that was highly resistant to NPA and was fully degrading it to inorganic nitrogen compounds and carbon dioxide. In order to understand the metabolic fate of NPA, we traced the fate of all atoms of the NPA molecule using isotope tracing experiments with [15N]NPA and [1-13C]NPA, in addition to experiments with uniformly 13C-labeled biomass that was used to follow the incorporation of 12C atoms from [U-12C]NPA into tricarboxylic acid cycle intermediates. With the help of genomics and transcriptomics, we uncovered the isolate’s NPA degradation pathway, which involves a putative propionate-3-nitronate monooxygenase responsible for the first step of NPA degradation. The discovered protein shares only 32% sequence identity with previously described propionate-3-nitronate monooxygenases. Finally, we advocate that NPA-degrading bacteria might find application in biotechnology, and their unique enzymes might be used in biosynthesis, bioremediation, and in dealing with postharvest NPA contamination in economically important products.IMPORTANCE Plants have evolved sophisticated chemical defense mechanisms, such as the production of plant toxins in order to deter herbivores. One example of such a plant toxin is nitropropionic acid (NPA), which is produced by leguminous plants and also by certain fungi. In this project, we have isolated a bacterium from the intestinal tract of a pest insect, the Southern green shield bug, that is able to degrade NPA. Through a multiomics approach, we identified the respective metabolic pathway and determined the metabolic fate of all atoms of the NPA molecule. In addition, we provide a new genetic marker that can be used for genome mining toward NPA degradation. The discovery of degradation pathways of plant toxins by environmental bacteria opens new possibilities for pretreatment of contaminated food and feed sources and characterization of understudied enzymes allows their broad application in biotechnology.

Identification and Characterization of a Cryptic Bifunctional Type I Diterpene Synthase Involved in Talaronoid Biosynthesis from a Marine-Derived Fungus.

We report the identification of the tnd biosynthetic cluster from the marine-derived fungus Aspergillus flavipes and the in vivo characterization of a cryptic type I diterpene synthase. The heterologous expression of the bifunctional terpene synthase led to the discovery of a diterpene backbone, talarodiene, harboring a benzo[a]cyclopenta[d]cyclooctane tricyclic fused ring system. The conversion of geranylgeranyl diphosphate to talarodiene was investigated using 13C-labeling studies, and stable isotope tracer experiments showed the biotransformation of talarodiene into talaronoid C.

Root-Zone CO2 Concentration Affects Partitioning and Assimilation of Carbon in Oriental Melon Seedlings.

Root-zone CO2 is essential for plant growth and metabolism. However, the partitioning and assimilation processes of CO2 absorbed by roots remain unclear in various parts of the oriental melon. We investigated the time at which root-zone CO2 enters the oriental melon root system, and its distribution in different parts of the plant, using 13C stable isotopic tracer experiments, as well as the effects of high root-zone CO2 on leaf carbon assimilation-related enzyme activities and gene expressions under 0.2%, 0.5% and 1% root-zone CO2 concentrations. The results showed that oriental melon roots could absorb CO2 and transport it quickly to the stems and leaves. The distribution of 13C in roots, stems and leaves increased with an increase in the labeled root-zone CO2 concentration, and the δ13C values in roots, stems and leaves increased initially, and then decreased with an increase in feeding time, reaching a peak at 24 h after 13C isotope labeling. The total accumulation of 13C in plants under the 0.5% and 1% 13CO2 concentrations was lower than that in the 0.2% 13CO2 treatment. However, the distributional proportion of 13C in leaves under 0.5% and 1% 13CO2 was significantly higher than that under the 0.2% CO2 concentration. Photosynthetic carbon assimilation-related enzyme activities and gene expressions in the leaves of oriental melon seedlings were inhibited after 9 days of high root-zone CO2 treatment. According to these results, oriental melon plants’ carbon distribution was affected by long-term high root-zone CO2, and reduced the carbon assimilation ability of the leaves. These findings provide a basis for the further quantification of the contribution of root-zone CO2 to plant communities in natural field conditions.

Ligand-induced electronic structure and morphology regulation in Ni3S2 heterostructures for efficient bifunctional electrocatalysis

Developing highly efficient and robust transition metal-based electrocatalysts for urea and sulfion electrolysis is crucial to the development of sustainable and clean hydrogen energy, however, is still a significant challenge. Herein, we reported a one-step synthetic protocol to fabricate terephthalic acid (TPA) anchored Ni3S2 (TPA-Ni3S2) brush-shaped nanoarrays on nickel foam (NF) skeleton. The introduction of TPA ligands simultaneously regulates the charge transfer and morphology of Ni3S2, thus optimizing the adsorption strength and increasing the number of active sites, thereby improving the catalytic performance. The optimized TPA@Ni3S2/NF exhibits superior electrocatalytic performance toward urea oxidation reaction (UOR) with a low overpotential of 1.0 V at 100 mA cm−2 and excellent operation stability, outperforming the benchmarks and many other previous reported Ni-based catalysts. More excitingly, as for sulfion oxidation reaction (SOR), the TPA@Ni3S2/NF also shows excellent activity, which merely requires 0.48 V to achieve current densities of 100 mA cm−2. Researches of the mechanism by XPS and in-situ Raman spectroscopy revealed abundant active NiOOH derivatives originated from the surface reconstruction of TPA@Ni3S2/NF, which promoted the excellent electrocatalytic performance towards UOR. In-situ DEMS isotope tracing experiments revealed the generation of N2 was derived from urea intermolecular N–N coupling. Ex-UV–vis and in-situ UV–vis spectra further disclosed the reaction mechanism that S2− was oxidized to short-chain polysulfides that were further combined to generate S8. This work provides a feasible strategy and deep understanding to design cost-efficient electrocatalysts for energy-saving hydrogen production and simultaneously eliminating wastewater pollutants.

Skin fibroblast metabolomic profiling reveals that lipid dysfunction predicts the severity of Friedreich’s ataxia

Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a triplet guanine-adenine-adenine (GAA) repeat expansion in intron 1 of the FXN gene, which leads to decreased levels of the frataxin protein. Frataxin is involved in the formation of iron-sulfur (Fe-S) cluster prosthetic groups for various metabolic enzymes. To provide a better understanding of the metabolic status of patients with FRDA, here we used patient-derived fibroblast cells as a surrogate tissue for metabolic and lipidomic profiling by liquid chromatography-high resolution mass spectrometry. We found elevated HMG-CoA and β-hydroxybutyrate-CoA levels, implying dysregulated fatty acid oxidation, which was further demonstrated by elevated acyl-carnitine levels. Lipidomic profiling identified dysregulated levels of several lipid classes in FRDA fibroblast cells when compared with non-FRDA fibroblast cells. For example, levels of several ceramides were significantly increased in FRDA fibroblast cells; these results positively correlated with the GAA repeat length and negatively correlated with the frataxin protein levels. Furthermore, stable isotope tracing experiments indicated increased ceramide synthesis, especially for long-chain fatty acid-ceramides, in FRDA fibroblast cells compared with ceramide synthesis in healthy control fibroblast cells. In addition, PUFA-containing triglycerides and phosphatidylglycerols were enriched in FRDA fibroblast cells and negatively correlated with frataxin levels, suggesting lipid remodeling as a result of FXN deficiency. Altogether, we demonstrate patient-derived fibroblast cells exhibited dysregulated metabolic capabilities, and their lipid dysfunction predicted the severity of FRDA, making them a useful surrogate to study the metabolic status in FRDA.

Isotope Calculation Gadgets: A Series of Software for Isotope-Tracing Experiments in Garuda Platform.

Isotope tracing is a powerful technique for elucidating intracellular metabolism. Experiments utilizing this technique involve various processes, such as the correction of natural isotopes. Although some previously developed software are available for these procedures, there are still time-consuming steps in isotope tracing including the creation of an isotope measurement method in mass spectrometry (MS) and the interpretation of obtained labeling data. Additionally, these multi-step tasks often require data format conversion, which is also time-consuming. In this study, the Isotope Calculation Gadgets, a series of software that supports an entire workflow of isotope-tracing experiments, was developed in the Garuda platform, an open community. Garuda is a graphical user interface-based platform that allows individual operations to be sequentially performed, without data format conversion, which significantly reduces the required time and effort. The developed software includes new features that construct channels for isotopomer measurements, as well as conventional functions such as natural isotope correction, the calculation of fractional labeling and split ratio, and data mapping, thus facilitating an overall workflow of isotope-tracing experiments through smooth functional integration.

Generation of interfacial high-spin manganese intermediates as reactive oxidant during peroxymonosulfate activation mediated by amorphous MnOx supported on polymeric substrate

The preparation of transition metal oxides based on traditional hydrothermal and calcination processes for heterogeneous PMS activation in contaminants' abatement has been widely reported. A satisfactory PMS activation efficiency often demands the transition metal oxides with crystallographic structure; however, the preparation processes of crystalline metal oxides require more energy input. Besides, achieving the targeted electron transfer between pollutants and reactive oxygen species (ROS) to overcome the disturbance of the actual water matrix is still challenging. Herein, we immobilized manganese oxides onto polymeric substrates under room temperature by a novel redox method with lower energy consumption. The obtained composite was applied for PMS activation to degrade multiple phenolic pollutants mainly through non-radical pathways. Combining the results of multiple characterizations and 18O isotope-tracer experiments, we proposed that the interfacial high-spin MnIII-peroxy complex was the primary reactive oxidant. Besides, a small portion of MnIII-peroxy complex could further undergo interspecies oxygen-transfer to form MnV-oxo species as the secondary reactive oxidant, resulting in the different manganese reduction products (MnIII/MnIV). The proposed mechanism could explain the average oxidation state of Mn changed after PMS activation. Comparing with the radical-based systems, interfacial reactive manganese intermediates exhibited satisfactory resistance against complex water matrices, such as chloride, bicarbonate, natural organic matter (NOM), and effluent organic matter (EfOM). We believe that this study could inspire novel methods with lower energy consumption to prepare active manganese oxides and provide intriguing mechanistic insights into PMS activation mediated by amorphous manganese oxides.

Abstract 1354: Regulation and roles of polyamines in CD8+ T cell fate and function

Abstract CD8+ T cells play central roles in tumor immune surveillance and are major effectors in adoptive cell therapy (ACT). Thus, strategies that enhance their functions are an urgent clinical need. Metabolic reprogramming determines T cell fate and function, where glycolysis principally drives an effector phenotype while oxidative phosphorylation (OxPhos) drives T cell memory [1]. However, the roles of amino acid catabolism in controlling effector and memory CD8+ T cell fate and function are less well understood [1, 2]. Glutamine is essential for nucleotide biosynthesis and as an anaplerotic fuel source for the tricarboxylic acid (TCA) cycle. Isotope tracing experiments with 13C glutamine or 13C arginine revealed that glutamine is the major source of polyamines in activated CD8+ T cells. Further, activation of CD8+ T cells provokes marked increases in the expression and activity of enzymes that direct polyamine biosynthesis, specifically ornithine decarboxylase (Odc), spermidine synthase (Srm) and spermine synthase (Sms), as well as to increases in the polyamines putrescine, spermidine and spermine. Notably, pharmacologic inhibition of Odc using difluoromethylornithine (DFMO), or genetic deletion of Odc using CD8+ T cells from CD4-Cre;Odcfl/fl mice, augments cytokine production in activated CD8+ T cells, including IFN-γ, TNF-α and granzyme B. Further, metabolic flux analysis indicates that DFMO treatment switches the metabolism of activated CD8+ T cells to rely on OxPhos, a phenotype found in CD8+ tissue resident memory (TRM) cells that play key roles in tissue and anti-tumor immunity anti-tumor reactivity. Indeed, inhibition or loss of Odc augments other TRM phenotypes, including increases in CD69high;CD44high;S1PR1low;CD62Llow cells that define the TRM phenotype. In addition, ACT of DFMO treated CD8+ T cells augments their survival in vivo and augments the generation of CD69+CD103+CD69+CXCR6+ and Ly6C+ TRMs in the bone marrow. Finally, DFMO treatment enhances IFN-γ and TNF-α production in human TILs, and co-treatment with TGF-β polarizes TILs into CD69+CD103+ and CD69+CD49a+ TRM-like cells. We conclude that polyamines are a metabolic check point in CD8+ TRM generation and are an actionable target to improve the anti-tumor immunity of T-cell based immunotherapies. Citation Format: Aya G. Elmarsafawi, Rebecca S. Hesterberg, John L. Cleveland. Regulation and roles of polyamines in CD8+ T cell fate and function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1354.

Sediment Nitrate Dissimilatory Reduction Processes along a Salinity Gradient in an Estuarine and Coastal Wetland, China

Nitrate (NO3−) dissimilatory reduction processes (denitrification, anammox and dissimilatory NO3− reduction to ammonium (DNRA)) in estuarine and coastal ecosystems play a crucial role in regulating reactive nitrogen loadings. However, nitrate reduction process rates and relative proportions along the estuarine salinity gradient remain poorly understood. Here, denitrification, anammox and DNRA were explored simultaneously along a salinity gradient in Yangtze Estuary based on nitrogen isotope-tracing experiments. Measured denitrification, anammox and DNRA process rates were in the range of 2.33–28.21 nmol g−1 h−1, 0.43–1.87 nmol g−1 h−1 and 0.28–0.74 nmol g−1 h−1, respectively, with a large spatio-temporal variation. The changes in these nitrate reduction process rates were mainly affected by the TOC, TN, NH4+ and NOx− concentrations, rather than salinity and related functional gene abundance. Denitrification dominated the total NO3− reduction process (67.52 to 93.85%), while anammox (3.67 to 25.01%) and DNRA (2.48 to 11.21%) also played a substantially important role in nitrate reduction. The proportions of denitrification to gross nitrate reduction in high-salinity areas were generally lower than those in freshwater, but the opposite was true for DNRA. Overall, our study reported the simultaneous observation of nitrate dissimilatory reduction processes along the salinity gradient of the estuary and highlighted that changes in sediment environmental variables affected by human activities can alter the distribution patterns of NO3− reduction processes.

ATF4 Protects the Heart From Failure by Antagonizing Oxidative Stress.

Cellular redox control is maintained by generation of reactive oxygen/nitrogen species balanced by activation of antioxidative pathways. Disruption of redox balance leads to oxidative stress, a central causative event in numerous diseases including heart failure. Redox control in the heart exposed to hemodynamic stress, however, remains to be fully elucidated. Pressure overload was triggered by transverse aortic constriction in mice. Transcriptomic and metabolomic regulations were evaluated by RNA-sequencing and metabolomics, respectively. Stable isotope tracer labeling experiments were conducted to determine metabolic flux in vitro. Neonatal rat ventricular myocytes and H9c2 cells were used to examine molecular mechanisms. We show that production of cardiomyocyte NADPH, a key factor in redox regulation, is decreased in pressure overload-induced heart failure. As a consequence, the level of reduced glutathione is downregulated, a change associated with fibrosis and cardiomyopathy. We report that the pentose phosphate pathway and mitochondrial serine/glycine/folate metabolic signaling, 2 NADPH-generating pathways in the cytosol and mitochondria, respectively, are induced by transverse aortic constriction. We identify ATF4 (activating transcription factor 4) as an upstream transcription factor controlling the expression of multiple enzymes in these 2 pathways. Consistently, joint pathway analysis of transcriptomic and metabolomic data reveal that ATF4 preferably controls oxidative stress and redox-related pathways. Overexpression of ATF4 in neonatal rat ventricular myocytes increases NADPH-producing enzymes' whereas silencing of ATF4 decreases their expression. Further, stable isotope tracer experiments reveal that ATF4 overexpression augments metabolic flux within these 2 pathways. In vivo, cardiomyocyte-specific deletion of ATF4 exacerbates cardiomyopathy in the setting of transverse aortic constriction and accelerates heart failure development, attributable, at least in part, to an inability to increase the expression of NADPH-generating enzymes. Our findings reveal that ATF4 plays a critical role in the heart under conditions of hemodynamic stress by governing both cytosolic and mitochondrial production of NADPH.

Alumina‐Supported Alpha‐Iron(III) Oxyhydroxide as a Recyclable Solid Catalyst for CO2 Photoreduction under Visible Light

AbstractPhotocatalytic conversion of CO2 into transportable fuels such as formic acid (HCOOH) under sunlight is an attractive solution to the shortage of energy and carbon resources as well as to the increase in Earth's atmospheric CO2 concentration. The use of abundant elements as the components of a photocatalytic CO2 reduction system is important, and a solid catalyst that is active, recyclable, nontoxic, and inexpensive is strongly demanded. Here, we show that a widespread soil mineral, alpha‐iron(III) oxyhydroxide (α‐FeOOH; goethite), loaded onto an Al2O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (λ&gt;400 nm) in the presence of a RuII photosensitizer and an electron donor. This system gave HCOOH as the main product with 80–90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm, as confirmed by isotope tracer experiments with 13CO2. The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO2.

Alumina-Supported Alpha-Iron(III) Oxyhydroxide as a Recyclable Solid Catalyst for CO2 Photoreduction under Visible Light.

Photocatalytic conversion of CO2 into transportable fuels such as formic acid (HCOOH) under sunlight is an attractive solution to the shortage of energy and carbon resources as well as to the increase in Earth's atmospheric CO2 concentration. The use of abundant elements as the components of a photocatalytic CO2 reduction system is important, and a solid catalyst that is active, recyclable, nontoxic, and inexpensive is strongly demanded. Here, we show that a widespread soil mineral, alpha‐iron(III) oxyhydroxide (α‐FeOOH; goethite), loaded onto an Al2O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (λ>400 nm) in the presence of a RuII photosensitizer and an electron donor. This system gave HCOOH as the main product with 80–90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm, as confirmed by isotope tracer experiments with 13CO2. The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO2.

Distinct N and C Cross-Feeding Networks in a Synthetic Mouse Gut Consortium.

ABSTRACTThe complex interactions between the gut microbiome and host or pathogen colonization resistance cannot be understood solely from community composition. Missing are causal relationships, such as metabolic interactions among species, to better understand what shapes the microbiome. Here, we focused on metabolic niches generated and occupied by the Oligo-Mouse-Microbiota (OMM) consortium, a synthetic community composed of 12 members that is increasingly used as a model for the mouse gut microbiome. Combining monocultures and spent medium experiments with untargeted metabolomics revealed broad metabolic diversity in the consortium, constituting a dense cross-feeding network with more than 100 pairwise interactions. Quantitative analysis of the cross-feeding network revealed distinct C and N food webs, highlighting the two Bacteroidetes members Bacteroides caecimuris and Muribaculum intestinale as primary suppliers of carbon and a more diverse group as nitrogen providers. Cross-fed metabolites were mainly carboxylic acids, amino acids, and the so far not reported nucleobases. In particular, the dicarboxylic acids malate and fumarate provided a strong physiological benefit to consumers, presumably used in anaerobic respiration. Isotopic tracer experiments validated the fate of a subset of cross-fed metabolites, such as the conversion of the most abundant cross-fed compound succinate to butyrate. Thus, we show that this consortium is tailored to produce the anti-inflammatory metabolite butyrate. Overall, we provide evidence for metabolic niches generated and occupied by OMM members that lays a metabolic foundation to facilitate an understanding of the more complex in vivo behavior of this consortium in the mouse gut.IMPORTANCE This article maps out the cross-feeding network among 10 members of a synthetic consortium that is increasingly used as the model mouse gut microbiota. Combining metabolomics with in vitro cultivations, two dense networks of carbon and nitrogen exchange are described. The vast majority of the ∼100 interactions are synergistic in nature, in several cases providing distinct physiological benefits to the recipient species. These networks lay the groundwork toward understanding gut community dynamics and host-gut microbe interactions.

Synergetic photocatalytic and thermocatalytic reforming of methanol for hydrogen production based on Pt@TiO2 catalyst

In order to efficiently produce H2, conventional methanol-water thermocatalytic (TC) reforming requires a very high temperature due to high Gibbs free energy, while the energy conversion efficiency of methanol-water photocatalytic (PC) reforming is far from satisfaction because of the kinetic limitation. To address these issues, herein, we incorporate PC and TC processes together in a specially designed reactor and realize simultaneous photocatalytic/thermocatalytic (PC-TC) reforming of methanol in an aqueous phase. Such a design facilitates the synergetic effect of the PC and TC process for H2 production due to a lower energy barrier and faster reaction kinetics. The methanol-water reforming based on the optimized 0.05%[email protected]2 catalyst delivers an outstanding H2 production rate in the PC-TC process (5.66 μmol H2·g–1 catalyst·s–1), which is about 3 and 7 times than those of the TC process (1.89 μmol H2·g–1 catalyst·s–1) and the PC process (0.80 μmol H2·g–1 catalyst·s–1), respectively. Isotope tracer experiments, active intermediate trapping experiments, and theoretical calculations demonstrate that the photo-generated holes and hydroxyl radicals could enhance the methanol dehydrogenation, water molecule splitting, and water-gas shift reaction, while high temperature accelerates reaction kinetics. The proposed PC-TC reforming of methanol for hydrogen production can be a promising technology to solve the energy and environmental issue in the closed-loop hydrogen economy in the near future.

Nitrogen recovery through fermentative dissimilatory nitrate reduction to ammonium (DNRA): Carbon source comparison and metabolic pathway

The dissimilatory nitrate reduction to ammonium (DNRA) process was known as a short circuit in nitrogen cycle, a key step in recovering nitrogen from nitrate wastewater, and has attracted people’s attention for a long time. Here, three organic substances supported DNRA systems, sodium succinate, glucose, and ethanol, were constructed in membrane bioreactor at three different COD/N ratios (6.5, 7.7, and 10) for nitrogen recovering from nitrate wastewater. The experiment results indicated that the maximum ammonium nitrogen transformation efficiency of 71.49%, 66.92%, and 92.05% were achieved at a COD/N ratio of 7.7 in sodium succinate, glucose, and ethanol supported DNRA systems. The high-throughput sequencing, which targeted nrfA gene, showed a greater diversity of DNRA microbiota at a COD/N ratio of 7.7. The quantitative PCR and 15N isotope tracing experiment showed that the ethanol-supported DNRA system had the highest nrfA gene abundance and DNRA potential rate. Meanwhile, ethanol-supported DNRA systems were found to contain a large number of fermenting bacteria (such as Acetoanerobium, Lentimicrobium, and Fusibacter), suggesting that anaerobic digestion may accompany the DNRA system. The potential metabolic pathways of three carbon sources were further predicted. Glucose and succinate may enter pyruvate metabolism via glycolysis and the citrate cycle. The high abundance of genes encoding phosphate acetyltransferase in ethanol system suggested that ethanol was most likely to be degraded via acetyl-CoA pathway and ensured electron supply to nitrate-reducing bacteria. This study is expected to provide new ideas for efficient recovery of nitrogen resources.

Unearthing the plant-microbe quid pro quo in root associations with beneficial fungi.

Mutualistic symbiotic associations between multicellular eukaryotes and their microbiota are driven by the exchange of nutrients in a quid pro quo manner. In the widespread arbuscular mycorrhizal (AM) symbiosis involving plant roots and Glomeromycotina fungi, the mycobiont is supplied with carbon through photosynthesis, which in return supplies the host plant with essential minerals such as phosphorus (P). Most terrestrial plants are largely dependent on AM fungi for nutrients, which raises the question of how plants that are unable to form a functional AM sustain their P nutrition. AM nonhost plants can form alternative, evolutionarily younger, mycorrhizal associations such as the ectomycorrhiza, ericoid and orchid mycorrhiza. However, it is unclear how plants such as the Brassicaceae species Arabidopsis thaliana, which do not form known mycorrhizal symbioses, have adapted to the loss of these essential mycorrhizal traits. Isotope tracing experiments with root-colonizing fungi have revealed the existence of new 'mycorrhizal-like' fungi capable of transferring nutrients such as nitrogen (N) and P to plants, including Brassicaceae. Here, we provide an overview of the biology of trophic relationships between roots and fungi and how these associations might support plant adaptation to climate change.

Investigation into the catalytic roles of oxygen vacancies during gaseous styrene degradation process via CeO2 catalysts with four different morphologies

CeO2 catalysts with four different morphologies (sphere, rod, octahedral and cube) were successfully synthesized under hydrothermal conditions and showed quite different thermocatalytic activities for gaseous styrene degradation. Unexpectedly, even though its main exposed lattice plane was (111), spherical CeO2 (CeO2-S), presented the highest styrene catalytic degradation activity (T90 =184 ℃) with a styrene degradation rate of 1.36 × 10−3 molstyrene g−1 h−1 at 200 ℃ that was approximately 12 times higher than that of cubic CeO2. A comprehensive structural characterization and mechanistic study found that the four CeO2 samples exhibit different degrees of lattice distortion and different oxygen vacancy concentrations. CeO2-S has the greatest lattice distortion, resulting in abundant oxygen vacancies. Oxygen vacancies were identified to be the main active sites through increasing reactive oxygen generation. Meanwhile, styrene was activated by adsorption of oxygen vacancies. Based on the results of in-situ DRIFTS and XPS measurements, 18O2 isotope tracing experiment and DFT theoretical calculations, the superior thermocatalytic performance of CeO2-S can be attributed to the lesser accumulation of intermediates on its surface, which follows the Langmuir-Hinshelwood (L-H) mechanism (low temperature) and the Mars-van Krevelen (MVK) mechanism (high temperature). In addition, no obvious decrease was observed in the activity of the CeO2-S catalyst for styrene degradation at 210 °C in the presence of water vapor, which is beneficial for the actual industrial application.

Isotope Tracing Experiment on the Mechanism of O2 on the Over-Thermal Decomposition of SF6

Isotope Tracing Experiment on the Mechanism of O2 on the Over-Thermal Decomposition of SF6