Methanogenesis in the presence of oxygenic photosynthetic bacteria may contribute to global methane cycle.

Accumulating evidences are challenging the paradigm that methane in surface water primarily stems from the anaerobic transformation of organic matters. Yet, the contribution of oxygenic photosynthetic bacteria, a dominant species in surface water, to methane production remains unclear. Here we show methanogenesis triggered by the interaction between oxygenic photosynthetic bacteria and anaerobic methanogenic archaea. By introducing cyanobacterium Synechocystis PCC6803 and methanogenic archaea Methanosarcina barkeri with the redox cycling of iron, CH4 production was induced in coculture biofilms through both syntrophic methanogenesis (under anoxic conditions in darkness) and abiotic methanogenesis (under oxic conditions in illumination) during the periodic dark-light cycles. We have further demonstrated CH4 production by other model oxygenic photosynthetic bacteria from various phyla, in conjunction with different anaerobic methanogenic archaea exhibiting diverse energy conservation modes, as well as various common Fe-species. These findings have revealed an unexpected link between oxygenic photosynthesis and methanogenesis and would advance our understanding of photosynthetic bacteria's ecological role in the global CH4 cycle. Such light-driven methanogenesis may be widely present in nature.

Abiotic Methane Production Driven by Ubiquitous Non-Fenton-Type Reactive Oxygen Species.

Abiotic CH4 production driven by Fenton-type reactive oxygen species (ROS) has been confirmed to be an indispensable component of the atmospheric CH4 budget. While the chemical reactions independent of Fenton chemistry to ROS are ubiquitous in nature, it remains unknown whether the produced ROS can drive abiotic CH4 production. Here, we first demonstrated the abiotic CH4 production at the soil-water interface under illumination. Leveraging this finding, polymeric carbon nitrides (CNx) as a typical analogue of natural geobattery material and dimethyl sulfoxide (DMSO) as a natural methyl donor were used to unravel the underlying mechanisms. We revealed that the ROS, photocatalytically produced by CNx, can oxidize DMSO into CH4 with a high selectivity of 91.5 %. Such an abiotic CH4 production process was further expanded to various non-Fenton-type reaction systems, such as electrocatalysis, pyrocatalysis and sonocatalysis. This work provides insights into the geochemical cycle of abiotic CH4, and offers a new route to CH4 production via integrated energy development.

Sustainable Conversion of Microplastics to Methane with Ultrahigh Selectivity by a Biotic-Abiotic Hybrid Photocatalytic System.

Efficient conversion of microplastics into fuels provides a promising strategy to alleviate environmental pollution and the energy crisis. However, the conventional processes are challenged by low product selectivity and potential secondary pollution. Herein, a biotic-abiotic photocatalytic system is designed by assembling Methanosarcina barkeri (M. b) and carbon dot-functionalized polymeric carbon nitrides (CDPCN), by which biodegradable microplastics-poly(lactic acid) after heat pretreatment can be converted into CH4 for five successive 24-day cycles with nearly 100 % CH4 selectivity by the assistance of additional CO2 . Mechanistic analyses showed that both photooxidation and photoreduction methanogenesis worked simultaneously via the fully utilizing photogenerated holes and electrons without chemical sacrificial quenchers. Further research validated the real-world applicability of M. b-CDPCN for non-biodegradable microplastic-to-CH4 conversion, offering a new avenue for engineering the plastic reuse.

All-Biobased Hydrovoltaic-Photovoltaic Electricity Generators for All-Weather Energy Harvesting.

Hygroelectricity generators (HEGs) utilize the latent heat stored in environmental moisture for electricity generation, but nevertheless are showing relatively low power densities due to their weak energy harvesting capacities. Inspired by epiphytes that absorb ambient moisture and concurrently capture sunlight for dynamic photosynthesis, we propose herein a scenario of all-biobased hydrovoltaic-photovoltaic electricity generators (HPEGs) that integrate photosystem II (PSII) with Geobacter sulfurreducens (G.s) for simultaneous energy harvesting from both moisture and sunlight. This proof of concept illustrates that the all-biobased HPEG generates steady hygroelectricity induced by moisture absorption and meanwhile creates a photovoltaic electric field which further strengthens electricity generation under sunlight. Under environmental conditions, the synergic hydrovoltaic-photovoltaic effect in HPEGs has resulted in a continuous output power with a high density of 1.24 W/m2, surpassing all HEGs reported hitherto. This work thus provides a feasible strategy for boosting electricity generation via simultaneous energy harvesting from ambient moisture and sunlight.

Sustained Biotic-Abiotic Hybrids Methanogenesis Enabled Using Metal-Free Black Phosphorus/Carbon Nitride.

Biotic-abiotic hybrid systems (BAHs) constructed by integrating biological methanogens with photocatalysts offer novel approaches for the effective solar-driven conversion of CO2 to CH4, providing significant inspiration for achieving carbon neutrality and alleviating the energy crisis. As metal photocatalysts would cause photocorrosion that damages microbial cells and lead to system imbalance. Therefore, exploring suitable metal-free photocatalysts is of particular importance in the search for more efficient and sustainable BAHs to improve the actual operability and applicability. Herein, black phosphorus/carbon nitride (BPCN x ) as an alternative metal-free heterostructure was combined with Methanosarcina barkeri (M. barkeri) to construct M. barkeri-BPCN x hybrid systems, and their cyclic methanogenesis performance was investigated. Our results demonstrated that BPCN x promotes the separation of photogenerated charges and enhances the quantum yield, providing a sustained energy source for the cyclically driven M. barkeri reduction of CO2 to CH4 under visible light. Our system achieved a total CH4 yield of 1087.45 ± 29.14 µmol gcat -1 after three cycles, 1.96 times higher than that of M. barkeri-Ni@CdS. M. barkeri-BPCN x overcame the defects of the metal photocatalyst and kept cell permeability, achieving cyclic stability and effectively maintaining the activity of M. barkeri. These results highlight the viable role of BPCN x as a metal-free photocatalysts in the construction of BAHs for the sustained and efficient methanation of CO2, which is conducive to the development of an environmentally-friendly, low-cost, and efficient strategy for the conversion of CO2 to CH4.

Metal-Free Semiconductor-Based Bio-Nano Hybrids for Sustainable CO2 -to-CH4 Conversion with High Quantum Yield.

Bio-nano hybrids with methanogens and nano-semiconductors provide an innovative strategy for solar-driven CO2 -to-CH4 conversion; however, the efficiency mismatch between electron production and utilisation results in low quantum yield and CH4 selectivity. Herein, we report the integration of metal-free polymeric carbon nitrides (CNx ) decorated with cyanamide (NCN) groups and Methanosarcina barkeri (M. b). The self-assembled M. b-NCN CNx exhibited a quantum yield of 50.3 % with 92.3 % CH4 selectivity under illumination, which outperforms other reported bio-nano hybrid systems and photocatalytic systems for CO2 reduction. This excellent performance was attributed to the distinct capacitance and conductive effects of NCN CNx , which promoted electron storage and redistribution at the biotic-abiotic interface to alleviate recombination losses and side reaction. This study provides new design guidelines for bio-nano hybrids for the sustainable photocatalytic reduction of CO2 into fuels.

Self-replicating Biophotoelectrochemistry System for Sustainable CO Methanation.

Efficient conversion of CO-rich gas to methane (CH4) provides an effective energy solution by taking advantage of existing natural gas infrastructures. However, traditional chemical and biological conversions face different challenges. Herein, an innovative biophotoelectrochemistry (BPEC) system using Methanosarcina barkeri-CdS as a biohybrid catalyst was successfully employed for CO methanation. Compared with CO2-fed BPEC, BPEC-CO significantly extended the CH4 producing time by 1.7-fold and exhibited a higher CH4 yield by 9.5-fold under light irradiation. This superior conversion of CO resulted from the fact that CO could serve as an effective quencher of reactive species along with the photoelectron production. In addition, CO was used as a carbon source either directly or indirectly via the produced CO2 for M. barkeri. Such a process improved the redox activities of membrane-bound proteins for BPEC methanogenesis. These results were consistent with the transcriptomic analyses, in which the genes for the putative CO oxidation and CO2 reduction pathways in M. barkeri were highly expressed, while the gene expression for reactive oxygen species detoxification remained relatively stable under light irradiation. This study has provided the first proof-of-concept evidence for sustainable CO methanation under a mild condition in the self-replicating BPEC system.

Biophotoelectrochemistry for renewable energy and environmental applications.

Biophotoelectrochemistry (BPEC) is an interdisciplinary research field and combines bioelectrochemistry and photoelectrochemistry through the utilization of the catalytic abilities of biomachineries and light harvesters to accomplish the production of energy or chemicals driven by solar energy. The BPEC process may act as a new approach for sustainable green chemistry and waste minimization. This review provides the state-of-the-art introduction of BPEC basics and systems, with a focus on light harvesters and biocatalysts, configurations, photoelectron transfer mechanisms, and the potential applications in energy and environment. Several examples of BPEC applications are discussed including H2 production, CO2 reduction, chemical synthesis, pollution control, and biogeochemical cycle of elements. The challenges about BPEC systems are identified and potential solutions are proposed. The review aims to encourage further research of BPEC toward development of practical BPEC systems for energy and environmental applications.

A facile and fast strategy for cathodic electroactive-biofilm assembly via magnetic nanoparticle bioconjugation.

Microbial electrosynthesis is a promising electricity-driven technology for converting carbon dioxide into value-added compounds, but the formation of cathodic electroactive-biofilms (CEBs) is challenging. Herein, we have demonstrated an innovative strategy for CEBs assembly via magnetic nanoparticle bioconjugation, which lies in the synergistic interactions among a bonder (Streptavidin, SA), conductive nanomaterials (Fe3O4), and a methanogen (M. barkeri). The results showed that the bioconjugated M. barkeri-SA-Fe3O4 biohybrids significantly enhanced both methane yield (33.2-fold) and faradaic efficiency (5.6-fold), compared with that of bare M. barkeri. Such an enhancement was attributed to the improved viability of CEBs with a higher biomass density. Particularly, more live cells were presented in the inner biofilms and promoted the long-distance electron exchange between the live outer-layer biofilm and the cathode electrode. Meanwhile, the higher redox activity of CEBs with the M. barkeri-SA-Fe3O4 biohybrids resulted in an improved transient charge storage capability, which was beneficial for the biological CO2-to-CH4 conversion via acting as an additional electron donor. This work has provided a new approach to accelerate the formation of CEBs and subsequent electron transfer, which holds a great potential for accomplishing electrosynthesis and CO2 fixation.

Duck enteritis virus infection suppresses viability and induces apoptosis and endoplasmic reticulum stress in duck embryo fibroblast cells via the regulation of Ca2.

Duck viral enteritis (DVE) is a lethal viral disease caused by duck enteritis virus (DEV) via an unknown mechanism. This study explores the relationship between Chinese standard challenge strain DEV (DEV-CSC)-induced apoptosis and endoplasmic reticulum stress (ERS) in duck embryo fibroblast (DEF) cells. Here we examined changes in Ca2+ concentration, cell proliferation, apoptosis, and the differential expression of C/EBP homologous protein (CHOP), glucose regulatory protein 78 (GRP78), and activating transcription factor 6 (ATF6) in infected cells. The results revealed that DEV-CSC infection significantly decreased Ca2+ concentration, suppressed cell viability, and induced apoptosis in DEF cells. Further experiments also demonstrated that DEV-CSC infection significantly upregulates CHOP, GRP78, and ATF6 expression. In addition, we show that the addition of ethylenediaminetetraacetic acid (EDTA) reverses the induction of apoptosis and the ERS mediated inhibition of cell viability in DEF cells associated with DEV-CSC infection. Therefore, we can conclude that infection with DEV-CSC induces apoptosis and ERS reducing the viability of DEF cells via the regulation of Ca2+. These findings may provide a new target for the treatment of DVE.

Extracellular polymeric substances trigger an increase in redox mediators for enhanced sludge methanogenesis.

Artificial redox mediators can be employed to improve the electron transfer efficiency during sludge methanogenesis, whereas these artificial redox mediators have possible deficiencies, such as high cost and non-biodegradability. For large-scale commercial applications, more cost-effective and environmentally friendly alternatives should be developed. Herein, the potential of extracellular polymeric substances (EPS) as natural redox mediators to improve methanogenesis was investigated. Compared to the control test without EPS addition, the methane (CH4) production yield was increased by 83.5 ± 2.4% with an EPS dosage of 0.50 g/L and the lag phase duration was shortened by 45.6 ± 7.0%, along with the enhanced sludge dewaterability. Spectroelectrochemical measurements implied that EPS addition notably changed the intensities of different redox-active groups, which decreased the charge transfer resistance and enhanced the extracellular electron transfer efficiency. These redox-active groups were mainly from the solubilization and hydrolysis of sludge protein due to increased protease activities, thereby leading to a higher acetate concentration during the acidification step. Further investigation showed that EPS addition also improved the activities of both acetotrophic and hydrogenotrophic methanogens, as indicated by a higher abundance of alpha subunit of methyl coenzyme M reductase (mcrA) genes, enhancing CH4 production. This work provides an innovative strategy for improving sludge anaerobic digestion with efficient additives.

Phosphate recovery with granular acid-activated neutralized red mud: Fixed-bed column performance and breakthrough curve modelling.

Granular acid-activated neutralized red mud (AaN-RM) has been successfully prepared with good chemical stability and physical strength. However, its potential for industrial application remains unknown. Therefore, the performance of granular AaN-RM for phosphate recovery in a fixed-bed column was investigated. The results demonstrated that the phosphate adsorption performance of granular AaN-RM in a fixed-bed column was affected by various operational parameters, such as the bed depth, flow rate, initial solution pH and initial phosphate concentration. With the optimal empty-bed contact time (EBCT) of 24.27 min, the number of processed bed volumes and the phosphate adsorption capacity reached 496.95 and 84.80 mg/g, respectively. Then, the saturated fixed-bed column could be effectively regenerated with a 0.5 mol/L HCl solution. The desorption efficiency remained as high as 83.45% with a low weight loss of 3.57% in the fifth regeneration cycle. In addition, breakthrough curve modelling showed that a 5-9-1 feed-forward artificial neural network (ANN) could be effectively applied for the optimization of the fixed-bed adsorption system; the coefficient of determination (R2) and the root mean square error (RMSE) evaluated on the validation-testing data were 0.9987 and 0.0183, respectively. Therefore, granular AaN-RM fixed-bed adsorption exhibits promising potential for phosphate removal and recovery from polluted water.

Graphite-assisted electro-fermentation methanogenesis: Spectroelectrochemical and microbial community analyses of cathode biofilms.

The stimulatory effect of conductive particles on anaerobic digestion has been demonstrated in recent years. However, it is yet to be determined whether and how conductive particles affect methanogenesis via electro-fermentation (electro-fermentation methanogenesis). In this study, it was demonstrated, for the first time, that conductive graphite boosted the methane production yield by 54.3% and increased the maximum methane production rate by 72.2% during electro-fermentation methanogenesis. Graphite significantly affected the composition of cathode biofilms, with more live and large aggregates being observed. Spectroelectrochemical analyses further showed that the kinds and intensities of biocatalytic active sites and redox groups on the cathode biofilms increased during graphite-assisted electro-fermentation methanogenesis. Particularly, c-type cytochromes, humic acid-like substances, and humic substances improved the long-range electron transport to methanogens such as Methanobacterium and Methanosarcina. The results have implications for the improvement of electro-fermentation process and the use of conductive materials for biofuel recovery.

Response of enhanced sludge methanogenesis by red mud to temperature: Spectroscopic and electrochemical elucidation of endogenous redox mediators.

Adding conductive materials can promote methanogenesis via facilitating electron exchange between syntrophic bacteria and methanogenic archaea. However, little is known about how temperature would interact with such an addition and thus affect the compositions and characteristics of endogenous redox mediators (ERMs). In particular, it is of strong interest to understand how the temperature variation would affect the improvement on methanogenesis induced by ERMs with conductive materials. Herein, we have investigated the response of sludge methanogenesis to temperature variation (from 15 to 35 °C) and spectroscopically detected the ERMs induced by conductive red mud. It was demonstrated that the increasing temperature enhanced the stimulating effect of conductive red mud on methane accumulation, and the methane production potential showed a linear relationship with redox parameters such as areal capacitance (Ca), free charges (R2) and electron exchange capacity (EEC). 2DCOS spectra further indicated that ν(C-O) and δ(O-H) in humic acids, ß-turn type III amide I νs(C=O) in Cytochrome c, and δ(C-H) in amines and lipids became the main redox groups in ERMs at 35 °C with the addition of red mud. The model revealed that the contribution of ERMs to the CO2 reduction to CH4 increased from 35.2 ±â€¯1.4% to 58.6 ±â€¯1.5% when the temperature increased from 15 to 35 °C. Our finding that conductive materials stimulated the formation and electroactivity of ERMs with the increasing temperature during anaerobic digestion can have important implications for the improvement of engineered methanogenic processes.

Enhancing sludge methanogenesis with improved redox activity of extracellular polymeric substances by hematite in red mud.

Different conductive materials have been employed to stimulate direct interspecies electron transfer (DIET) during methanogenesis, but few studies have been concerned with the interaction between conductive materials and extracellular polymeric substances (EPS) such as the effect on sludge aggregation and redox activity of EPS. This study aims to systematically investigate the role of red mud with 45.46 wt% hematite on methanogenesis during the anaerobic digestion of waste activated sludge. The results showed that the multivalent cations from hematite effectively promoted the formation of large and compact aggregates, which might contribute to the rapid direct electron exchange during the DIET process. Meanwhile, more redox-active mediators including c-type cytochromes (c-Cyts) and humic substances, particularly in tight-bound EPS (TB-EPS), and more redox-active metals such as Fe introduced by red mud could take part in the interspecies electron transfer process between syntrophic bacteria and methanogenic archaea, which also promoted methane production (35.52 ±â€¯2.64% increase compared with the control). This study provided initial scientific evidence to comprehensively assess the role of conductive materials during methanogenesis, with important implications for the biogeochemical redox processes of conductive minerals in natural and engineered environments.

Red mud enhances methanogenesis with the simultaneous improvement of hydrolysis-acidification and electrical conductivity.

The role of red mud in the improvement of methanogenesis during sludge anaerobic digestion was innovatively investigated in this study. The results demonstrated that the addition of 20g/L red mud resulted in a 35.5% increase in methane accumulation. Red mud effectively promoted the hydrolysis-acidification of organic compounds in the sludge, which resulted in the increase of protein, polysaccharide, and VFAs by 5.1-94.5%. The activities of key enzymes were improved by 41.4-257.3%. Electrochemical measurements presented direct evidence that the electrical conductivity was significantly improved with red mud. More conductive magnetite was formed during the secondary mineralization after Fe(III) reduction by Fe (III)-reducing genes such as Clostridiaceae and Ruminococcaceae. The higher conductivity enhanced the electron transfer between the syntrophic bacteria (Geobacteraceae) and methanogens (Methanosaeta and Methanosarcina), and then improved the methanogenesis. This research provides a novel perspective on the synergism between sludge and red mud for methane production.

Systematic Study on Hydrated Arginine: Clear Theoretical Evidence for the Canonical-to-Zwitterionic Structure Transition.

Extensive ab initio investigations have been performed to characterize the stable conformers of hydrated arginine (Arg-H2O). Many new low-energy canonical Arg-H2O conformers were identified and they are more stable than previous results. The large energy differences (more than 5.00 kcal mol-1) between the canonical and zwitterionic Arg-H2O isomers calculated by the composite CBS-QB3 method confirmed the dominance of the zwitterions. The micro effects of corrections of the zero-point energy and the basis set superposition error on the stability of hydrated isomers were carefully examined for the first time. The infrared (IR) spectra were simulated at a recommended temperature and the notable spectral differences enable the unambiguous identification of the different hydrated forms. Further transition state calculations revealed that the canonical Arg-H2O can be transformed to the zwitterions using the amino group as a bridge. Our study thus shows valuable insights into the hydration of large flexible molecules and provides solid theoretical evidence for the canonical-to-zwitterionic structure transition of hydrated arginine.

A floor-map-aided WiFi/pseudo-odometry integration algorithm for an indoor positioning system.

This paper proposes a scheme for indoor positioning by fusing floor map, WiFi and smartphone sensor data to provide meter-level positioning without additional infrastructure. A topology-constrained K nearest neighbor (KNN) algorithm based on a floor map layout provides the coordinates required to integrate WiFi data with pseudo-odometry (P-O) measurements simulated using a pedestrian dead reckoning (PDR) approach. One method of further improving the positioning accuracy is to use a more effective multi-threshold step detection algorithm, as proposed by the authors. The "go and back" phenomenon caused by incorrect matching of the reference points (RPs) of a WiFi algorithm is eliminated using an adaptive fading-factor-based extended Kalman filter (EKF), taking WiFi positioning coordinates, P-O measurements and fused heading angles as observations. The "cross-wall" problem is solved based on the development of a floor-map-aided particle filter algorithm by weighting the particles, thereby also eliminating the gross-error effects originating from WiFi or P-O measurements. The performance observed in a field experiment performed on the fourth floor of the School of Environmental Science and Spatial Informatics (SESSI) building on the China University of Mining and Technology (CUMT) campus confirms that the proposed scheme can reliably achieve meter-level positioning.

Extensive computational study on coordination of transition metal cations and water molecules to glutamic acid.

On the basis of the conformations of glutamic acid (Glu) and analysis of possible metal cation coordination and hydration modes, conformations of Glu metalated with transition metal cations (TMCs), Cu(+/2+), Zn(+/2+), and Fe(+/2+/3+) and hydrations of Glu-Cu(+/2+) and Glu-Zn(+/2+) complexes by up to three water molecules are determined by extensive computational searches. The BHandHLYP functional is chosen as the main computational method as its overall performance for treating the spin multiplicity of TMCs is similar to that of CCSD(T) and better than that of MP2 and B3LYP. All mono- and divalent TMCs prefer tridentate coordination to canonical Glu, while Fe(3+) favors a bidentate coordination to zwitterionic Glu. The ground state of Glu-Fe(+) is found to be a spin sextet. Metal ion affinities of Glu for the TMCs are determined, and an excellent agreement with the experiment for Cu(+) may be obtained if the entropic effect is properly accounted for. Effects of hydration on the stabilities of different Glu-Cu(+/2+)/Zn(+/2+) structures are discussed, and the hydration energies for up to three water molecules are obtained. For the global minimum to take the zwitterionic form, Glu-Zn(+) requires only monohydration, Glu-Zn(2+) needs to be trihydrated, while Glu-Cu(+/2) should be hydrated with four or more water molecules.

Comparison of lifestyle and living environment among high risk immigrant and low risk host residents: implications for esophageal cancer etiology.

BACKGROUND: It has been hypothesized that the high prevalence of esophageal squamous cell carcinoma (ESCC) in China is associated with specific environments and lifestyles. A previous study found that immigrant residents (IR) from Henan, residing long term in the town of Caihu, had significantly greater risk of dying from ESCC than host residents (HR). OBJECTIVES: This study was conducted to compare lifestyle and living environments between high risk IR and low risk HR to determine risk factors for ESCC. METHODS: The subjects included randomly selected IR and HR living in Caihu. Information on lifestyle and the living environment of participants was collected by interview using a structured questionnaire. RESULTS: The IR were found to have a higher consumption of hot food (P<0.05), pickled vegetables (P<0.05) and a lower consumption of fresh fruits and vegetables, and alcohol (P<0.05), compared with the HR. There were no significant differences in income and cigarette smoking between the two populations. Fewer IR families had a separate kitchen (P<0.05) than host families. CONCLUSIONS: Our study provided some epidemiological evidence indicating that dietary factors, such as hot food, pickled vegetables, salt, and low fruit and vegetable intake, as well as a poor living environment, are possibly related to the higher prevalence of ESCC in IR. However, cigarette smoking, alcohol drinking and income were not shown to be risk factors for immigrant susceptibility to ESCC in our study.