Mechanism of extracellular electron transport and reactive oxygen mediated Sb(III) oxidation by Klebsiella aerogenes HC10.

Microbial oxidation and the mechanism of Sb(III) are key governing elements in biogeochemical cycling. A novel Sb oxidizing bacterium, Klebsiella aerogenes HC10, was attracted early and revealed that extracellular metabolites were the main fractions driving Sb oxidation. However, linkages between the extracellular metabolite driven Sb oxidation process and mechanism remain elusive. Here, model phenolic and quinone compounds, i.e., anthraquinone-2,6-disulfonate (AQDS) and hydroquinone (HYD), representing extracellular oxidants secreted by K. aerogenes HC10, were chosen to further study the Sb(III) oxidation mechanism. N2 purging and free radical quenching showed that oxygen-induced oxidation accounted for 36.78% of Sb(III) in the metabolite reaction system, while hydroxyl free radicals (·OH) accounted for 15.52%. ·OH and H2O2 are the main driving factors for Sb oxidation. Radical quenching, methanol purification and electron paramagnetic resonance (EPR) analysis revealed that ·OH, superoxide radical (O2•-) and semiquinone (SQ-•) were reactive intermediates of the phenolic induced oxidation process. Phenolic-induced ROS are one of the main oxidants in metabolites. Cyclic voltammetry (CV) showed that electron transfer of quinone also mediated Sb(III) oxidation. Part of Sb(V) was scavenged by the formation of the secondary Sb(V)-bearing mineral mopungite [NaSb(OH)6] in the incubation system. Our study demonstrates the microbial role of oxidation detoxification and mineralization of Sb and provides scientific references for the biochemical remediation of Sb-contaminated soil.

Highly enhanced removal of Cr(VI) by nZVI in presence of myo-inositol hexakisphosphate: The depassivation performance and multiple electron transfer mechanisms.

The capability of traditional ligand in countering rapid passivation on nanoscale zero-valent iron (nZVI) surface is inadequate, and the precise electron transfer mechanism remains elusive. In this study, we reported that myo-inositol hexakisphosphate (IHP), a redox-inactive organophosphorus in soil, could highly enhance Cr(VI) reduction and immobilization in comparison with typical ligands (TPP, EDTA, oxalate and phosphate). And the effects of IHP concentration, Cr(VI) concentration and initial pH were systematically investigated. Cr K-edge XANES and XPS analysis revealed that Cr(III) was the exclusive form in solid products regardless of IHP existence. Results of ATR-FTIR and FESEM inferred that IHP was adsorbed on nZVI surface via inner-sphere complexation, thus averting encapsulation of [Fe, Cr](OH)3 coprecipitate and impeding solid particles agglomeration. Additionally, IHP expedited the production of surface-bound Fe(II), primarily attributable to the interaction between nZVI and oxygen. These surface-bound Fe(II) species played a pivotal role in Cr(VI) reduction. Electrochemical analysis unveiled that IHP lowered redox potential of Fe(III)/Fe(II), thereby facilitating reaction between Fe(II) and Cr(VI), whereas inhibited direct electron transfer from nZVI core to Cr(VI). Our findings proposed a novel potential ligand for alleviating nZVI passivation in Cr(VI) removal and deepened our understanding in the process of electron transfer.

In situ growth of iron incorporated Ni3S2 nanosheet on nickel foam in mediating electron transfer to peroxymonosulfate for pollutant abatement.

Catalytic oxidation of organic pollutants is a well-known and effective technique for pollutant abatement. Unfortunately, this method is significantly hindered in practical applications by the low efficiency and difficult recovery of the catalysts in a powdery form. Herein, a three-dimensional (3D) framework of Fe-incorporated Ni3S2 nanosheets in-situ grown on Ni foam (Fe-Ni3S2@NF) was fabricated by a facile two-step hydrothermal process and applied to trigger peroxymonosulfate (PMS) oxidation of organic compounds in water. A homogeneous growth environment enabled the uniform and scalable growth of Fe-Ni3S2 nanosheets on the Ni foam. Fe-Ni3S2@NF possessed outstanding activity and durability in activating PMS, as it effectively facilitated electron transfer from organic pollutants to PMS. Fe-Ni3S2@NF initially supplied electrons to PMS, causing the catalyst to undergo oxidation, and subsequently accepted electrons from organic compounds, returning to its initial state. The introduction of Fe into the Ni3S2 lattice enhanced electrical conductivity, promoting mediated electron transfer between PMS and organic compounds. The 3D conductive Ni foam provided an ideal platform for the nucleation and growth of Fe-Ni3S2, accelerating pollutant abatement due to its porous structure and high conductivity. Furthermore, its monolithic nature simplified the catalyst recycling process. A continuous flow packed-bed reactor by encapsulating Fe-Ni3S2@NF catalyst achieved complete pollutant abatement with continuous operation for 240 h, highlighting its immense potential for practical environmental remediation. This study presents a facile synthesis method for creating a novel type of monolithic catalyst with high activity and durability for decontamination through Fenton-like processes.

Construction of eco-friendly dual carbon dots ratiometric fluorescence probe for highly selective and efficient sensing mercury ion.

In present work, blue carbon dots (b-CDs) were derived from ammonium citrate and guanidine hydrochloride, and red carbon dots (r-CDs) were stemmed from malonate, ethylenediamine and meso­tetra (4-carboxyphenyl) porphin based on facile hydrothermal method. Eco-friendly ratiometric fluorescence probe was innovatively constructed to effectively measure Hg2+ utilizing b-CDs and r-CDs. The developed probe displayed two typical emission peaks at 450 nm from b-CDs and 650 nm from r-CDs under the excitation at 360 nm. Mercury ion has strong quenching effect on the fluorescence intensity at 450 nm due to the electron transfer process and the fluorescence change at 450 nm was used as the response signal, whereas the fluorescence intensity at 650 nm kept unchangeable which resulted from the chemical inertness between Hg2+ and r-CDs, serving as the reference signal in the sensing system. Under optimal circumstances, this probe exhibited an excellent linearity between the fluorescence response values of ΔF450/F650 and Hg2+ concentrations over range of 0.01-10 µmol/L, and the limit of detection was down to 5.3 nmol/L. Furthermore, this probe was successfully employed for sensing Hg2+ in practical environmental water samples with satisfied recoveries of 98.5%-105.0%. The constructed ratiometric fluorescent probe provided a rapid, environmental-friendly, reliable, and efficient platform for measuring trace Hg2+ in environmental field.

Sludge-derived hydrochar modulates complete nonradical electron transfer in peroxydisulfate activation via pyrrolic-N and carbon defect: Implication for degrading electron-rich ionizable anilines compounds.

Nonradical electron transfer process (ETP) is a promising pathway for pollutant degradation in peroxydisulfate-based advanced oxidation processes (PDS-AOPs). However, there is a critical bottleneck to trigger ETP by sludge-derived hydrochar due to its negatively charged surface, inferior porosity and electrical conductivity. Herein, pyrrolic-N doped and carbon defected sludge-derived hydrochar (SDHC-N) was constructed for PDS activation to degrade anilines ionizable organic compounds (IOC) through complete nonradical ETP oxidation. Degradation of anilines IOC was not only affected by the electron-donating capacity but also proton concentration in solution because of the ionizable amino group (-NH2). Diverse effects including proton favor, insusceptible and inhibition were observed. Impressively, addition of HCO3 with strong proton binding capacity boosted aniline degradation nearly 10 times. Moreover, characterizations and theoretical calculations demonstrated that pyrrolic-N increased electron density and created positively charged surface, profoundly promoting generation of SDHC-N-S2O82-* complexes. More delocalized electrons around carbon defect could enhance electron mobility. This work guides a rational design of sludge-derived hydrochar to mediate nonradical ETP oxidation, and provides insights into the impacts of proton on anilines IOC degradation.

Enhancement of anaerobic treatment of antibiotic pharmaceutical wastewater through the development of iron-based and carbon-based materials: A critical review.

The extensive use of antibiotics has created an urgent need to address antibiotic wastewater treatment, posing significant challenges for environmental protection and public health. Recent advances in the efficacy and mechanisms of conductive materials (CMs) for enhancing the anaerobic biological treatment of antibiotic pharmaceutical wastewater are reviewed. For the first time, the focus is on the various application forms of iron-based and carbon-based CMs in strengthening the anaerobic methanogenic system. This includes the use of single CMs such as zero-valent iron (ZVI), magnetite, biochar (BC), activated carbon (AC), and graphene (GP), as well as iron-based and carbon-based composite CMs with diverse structures. These structures include mixed, surface-loaded, and core-shell combinations, reflecting the development of CMs. Iron-based and carbon-based CMs promote the rapid removal of antibiotics through adsorption and enhanced biodegradation. They also mitigate the inhibitory effects of toxic pollutants on microbial activity and reduce the expression of antibiotic resistance genes (ARGs). Additionally, as effective electron carriers, these CMs enrich microorganisms with direct interspecies electron transfer (DIET) functions, accelerate interspecies electron transfer, and facilitate the conversion of organic matter into methane. Finally, this review proposes the use of advanced molecular detection technologies to clarify microbial ecology and metabolic mechanisms, along with microscopic characterization techniques for the modification of CMs. These methods can provide more direct evidence to analyze the mechanisms underlying the cooperative anaerobic treatment of refractory organic wastewater by CMs and microorganisms.

Genome-centric metagenomic analysis reveals mechanisms of quorum sensing promoting anaerobic digestion under sulfide stress: Syntrophic metabolism and microbial self-adaptation.

Sulfide stress is a common inhibition factor in anaerobic digestion systems with sulfur-rich feedstocks. Quorum sensing (QS) signaling molecule N-acyl-homoserine lactones (AHLs) possess positive effect on promoting anaerobic digestion. However, the micro-biological mechanisms of AHLs affecting syntrophic metabolism and microbial self-adaptation have not yet been deciphered in anaerobic digestion under sulfide stress. In this study, the CH4 production increased by 21.34 % at 20 µM AHLs addition in anaerobic digestion under sulfide stress. AHLs contributed to establishing potential syntrophic relationship between acidifying bacteria (unclassified_o__Bacteroidales, Lentimicrobium, Acetoanaerobium, Longilinea, and Sphaerochaetaa) and Methanothrix. AHLs promoted syntrophic metabolism by boosting microbial metabolic activity and interspecies electron transfer (IET) process under sulfide stress. For microbial metabolic activity, AHLs promoted the key enzyme synthesis in acidogenesis and methanogenesis. For IET process, AHLs promoted the assembly and synthesis of conductive pili, and synthesis and secretion of riboflavin. Furthermore, AHLs promoted microbial self-adaptation including two component system, lipopolysaccharide biosynthesis, and DNA repair, which were important evidences that microbial resistance to sulfide stress was enhanced by AHLs. Microbial self-adaptation provided favorable foundation and safeguard for syntrophic metabolisms under sulfide stress. These findings deciphered the micro-biological mechanisms of AHLs enhancing anaerobic digestion under sulfide stress.

Protein-driven interaction enhanced electrochemiluminescence biosensor of hydrogen-bonded biohybrid organic frameworks for sensitive immunoassay of disease markers.

The oriented design of reticular materials as emitters can significantly enhance the sensitivity of electrochemiluminescence (ECL) sensing analysis for disease markers. However, due to the structural fragility of hydrogen bonds, relational research on hydrogen-bonded organic frameworks (HOFs) has not been thoroughly conducted. Additionally, the modulation of luminescence behavior through HOFs has been rarely reported. In view of this, hydrogen-bonded biohybrid organic frameworks (HBOFs) were synthesized and recruited for ECL immunoassay applications. HBOFs was easily prepared using 6,6',6″,6‴-(pyrene-1,3,6,8-tetrayl)tetrakis(2-naphthoic acid) as linkers via bovine serum albumin (BSA) activated hydrogen-bonded cross-linking. The material exhibited good fluorescence emission characteristics. And the highly ordered topological structure and molecular motion limitation mediated by BSA overcome aggregation-caused quenching and generate strong aggregation induced emission, expressing hydrogen-bond interaction enhanced ECL (HIE-ECL) activity with the participation of tri-n-propylamine. Furthermore, a sandwich immunosensor was constructed employing cobalt-based metal-phenolic network (CMPN) coated ferrocene nanoparticles (FNPs) as quenchers (CMPN@FNPs). Signal closure can be achieved by annihilating the excited state through electron transfer from both CMPN and FNPs. Using a universal disease marker, carcinoembryonic antigen, as the analysis model, the signal-off sensor obtained a detection limit of 0.47 pg/mL within the detection range of 1 pg/mL - 50 ng/mL. The synthesis and application of highly stable HBOFs triggered by proteins provide a reference for the development of new reticular ECL signal labels, and electron transfer model provides flexible solutions for more sensitive sensing analysis.

Exploring the relationship between metal ion valency and electron transfer in copigmentation processes of cyanidin-3-O-glucoside in simulated fruit wine solutions.

In this experiment, five metal ions (K+, Mg2+, Al3+, Ga3+, and Sn4+) were utilized as copigments to investigate their copigmentation processes with cyanidin-3-O-glucoside (C3OG) in simulated fruit wine solutions. The color characteristics were analyzed using Glories and CIELAB methods, and the copigmentation effects were determined spectrophotometrically. Thermodynamic parameters, including the equilibrium constant (K) and standard Gibbs free energy (ΔG°), were calculated to comprehend the binding affinity between metal ions and C3OG. Ultra-fast femtosecond spectroscopy was employed to monitor the photoinduced electron transfer process between C3OG and cations. Theoretical calculations were also conducted to support experimental findings. The results revealed that the presence of metal ions significantly enhanced the color intensity of C3OG in simulated fruit wine solutions. Higher valency cations, particularly Sn4+, Ga3+, and Al3+, exhibited superior copigmentation effects, resulting in significant bathochromic and hyperchromic changes. Thermodynamic analysis confirmed that the interaction between C3OG and metal ions was spontaneous and exothermic. Ultra-fast femtosecond spectroscopy demonstrated that electron transfer from C3OG to metal ions occurred, with the efficiency of transfer being dependent on valency. Theoretical calculations corroborated the experimental results by highlighting the role of metal ions in stabilizing C3OG/metal complexes through electron transfer. The findings presented in this study contribute to a more comprehensive understanding of pigment/metal complexes and the underlying chemistry behind fruit wine color. Furthermore, it advances the theoretical foundation of copigmentation and broadens its applications in the beverage industry.

Enhanced Extracellular Electron Transfer in Magnetite-Mediated Anaerobic Oxidation of Methane Coupled to Humic Substances Reduction: The Pivotal Role of Membrane-Bound Electron Transfer Proteins.

Humic substances are organic substances prevalent in various natural environments, such as wetlands, which are globally important sources of methane (CH4) emissions. Extracellular electron transfer (EET)-mediated anaerobic oxidation of methane (AOM)-coupled with humic substances reduction plays an important role in the reduction of methane emissions from wetlands, where magnetite is prevalent. However, little is known about the magnetite-mediated EET mechanisms in AOM-coupled humic substances reduction. This study shows that magnetite promotes the reduction of the AOM-coupled humic substances model compound, anthraquinone-2,6-disulfonate (AQDS). 13CH4 labeling experiments further indicated that AOM-coupled AQDS reduction occurred, and acetate was an intermediate product of AOM. Moreover, 13CH313COONa labeling experiments showed that AOM-generated acetate can be continuously reduced to methane in a state of dynamic equilibrium. In the presence of magnetite, the EET capacity of the microbial community increased, and Methanosarcina played a key role in the AOM-coupled AQDS reduction. Pure culture experiments showed that Methanosarcina barkeri can independently perform AOM-coupled AQDS reduction and that magnetite increased its surface protein redox activity. The metatranscriptomic results indicated that magnetite increased the expression of membrane-bound proteins involved in energy metabolism and electron transfer in M. barkeri, thereby increasing the EET capacity. This phenomenon potentially elucidates the rationale as to why magnetite promoted AOM-coupled AQDS reduction.

Coexisting ferrihydrite-enhanced contaminant degradation during pyrite oxygenation.

Oxygenation of pyrite (Py) is known to mediate generation of reactive oxygen species (ROS) with these species capable of inducing contaminants degradation, whereas the possible participation of coexisting Fe(III) minerals in these processes is still unclear. This study finds that freshly formed ferrihydrite (Fh) significantly enhances the Py-mediated sulfamethoxazole (SMX) degradation process. Through the 56Fe isotope tracer experiment and a series of control experiments, Fh is found to be reduced by Py to form secondary solid-phase Fe(II) species (Fe(II)RF) which in turn facilitates generation of H2O2 from the O2 reduction pathway. However, Py was found to mediate rapid structural transformation of Fh to form more thermodynamically stable goethite and hematite with these less redox active minerals unable to sustainably promote the Py-mediated SMX degradation process. Therefore, the improvement of Fh on Py-mediated SMX degradation process is not readily observable in reaction systems with low concentrations of coexisting Fh. In comparison, continuing input of 10 mM Fh increased the degradation efficiency of SMX by 60 % over three days. Our results demonstrate that the oxidative degradation of organic contaminants over the oxygenation of Py when coexisting with Fh can be more significant but currently underestimated.

Built-In Electric Field Boost Photocatalytic Degradation of Pollutants in Wastewater.

The photocatalysis technique shows significant potential for wastewater degradation; however, the rapid recombination of photogenerated holes and electrons severely limits its photocatalytic efficiency. This situation necessitates the development of effective strategies to tackle these challenges. One well-documented approach is built-in electric field engineering in heterojunctions or composites, which has been shown to enhance electron transfer and thereby reduce the recombination of electrons and holes. This strategy has proven highly effective in significantly improving photocatalytic activity for the degradation of pollutants in wastewater. In this context, we summarize recent advancements in built-in electric field engineering in photocatalysts, highlighting the fundamentals and modifications of this approach, as well as its positive impact on photocatalytic performance in the degradation of wastewater pollutants.

Fundamental Insights into the Direct Electron Transfer Mechanism on Ag Atomic Cluster.

The nonradical oxidation pathway for pollutant degradation in Fenton-like catalysis is favorable for water treatment due to the high reaction rate and superior environmental robustness. However, precise regulation of such reactions is still restricted by our poor knowledge of underlying mechanisms, especially the correlation between metal site conformation of metal atom clusters and pollutant degradation behaviors. Herein, we investigated the electron transfer and pollutant oxidation mechanisms of atomic-level exposed Ag atom clusters (AgAC) loaded on specifically crafted nitrogen-doped porous carbon (NPC). The AgAC triggered a direct electron transfer (DET) between the terminal oxygen (Oα) of surface-activated peroxodisulfate and the electron-donating substituents-containing contaminants (EDTO-DET), rendering it 11-38 times higher degradation rate than the reported carbon-supported metal catalysts system with various single-atom active centers. Heterocyclic substituents and electron-donating groups were more conducive to degradation via the EDTO-DET system, while contaminants with high electron-absorbing capacity preferred the radical pathway. Notably, the system achieved 79.5% chemical oxygen demand (COD) removal for the treatment of actual pharmaceutical wastewater containing 1053 mg/L COD within 30 min. Our study provides valuable new insights into the Fenton-like reactions of metal atom cluster catalysts and lays an important basis for revolutionizing advanced oxidation water purification technologies.

In Situ Loading of ZnS on the PPF-3 Surface for Enhancing Nonlinear Optical Performance.

In recent years, with the rapid development of ultrastrong and ultrafast lasers, it has become essential to develop new materials with excellent nonlinear optical (NLO) properties. Porphyrin-based metal-organic frameworks (MOFs) have great potential for application in the field of NLO due to their large conjugated structure and good stability. As a typical porphyrin-based MOF, porphyrin paddle-wheel framework-3 (PPF-3) has been prepared and applied in the fields of catalysis and sensing, yet the investigation of PPF-3 in NLO remains unexplored. In this study, the ZnS/PPF-3 composite was successfully prepared using a solvent thermal method to in situ load ZnS on the surface of PPF-3. Utilizing the Z-scan technique, the NLO properties of ZnS, PPF-3, and ZnS/PPF-3 composite were investigated under different input energy intensities. ZnS/PPF-3 composite material exhibits significantly enhanced NLO properties, with the third-order nonlinear absorption coefficient (ßeff) of up to 7.00 × 10-10 m/W and a limiting threshold as low as 1.52 J/cm2, indicating its promising application potential value in the field of optical limiting. To enhance the practical utility, the ZnS/PPF-3/PVA film was prepared via the drop-casting method, achieving a maximum ßeff of 5.00 × 10-8 m/W. The smaller optical bandgap of ZnS/PPF-3 and electron transfer from PPF-3 to ZnS are the key factors that enable the ZnS/PPF-3 composite to a superior NLO performance.

Approaches to determination of the mechanism of the Rieske monooxygenase salicylate 5-hydroxylase.

Rieske oxygenases catalyze an exceptionally broad range of discrete types of reactions despite the utilization of a highly conserved quaternary structure and metal cofactor complement. Oxygen activation within this family occurs at a mononuclear FeII site, which is located approximately 12 Å from a one-electron reduced Rieske-type iron-sulfur cluster. Electron transfer from the Rieske cluster to the mononuclear iron site occurs during O2 activation and product formation. A key question is whether all Rieske oxygenase reactions involve the same type of activated oxygen species. This question has been explored using the Rieske oxygenase salicylate 5-hydroxylase, which catalyzes both aromatic hydroxylation of salicylate and aromatic methyl hydroxylation when a methyl substituent is placed in the normal position of aromatic ring hydroxylation. We show here that the combined application of kinetic, biophysical, computational, and isotope effect methods reveals a uniform mechanism for initial O2 activation and substrate attack for both types of reactivity. However, the mechanism diverges during the later phases of the reactions in response to the electronic nature and geometry of the substrates as well as the lifetime of intermediates. Similar factors may be encountered broadly in the Rieske oxygenase family.

Substitution of the mononuclear, non-heme iron cofactor in lipoxygenases for structural studies.

This Chapter describes methods for the biosynthetic substitution of the mononuclear, non-heme iron in plant and animal lipoxygenases (LOXs). Substitution of this iron center for a manganese ion results in an inactive, yet faithful structural surrogate of the LOX enzymes. This metal ion substitution permits structural and dynamical studies of enzyme-substrate complexes in solution and immobilized on lipid membrane surfaces. Representative procedures for two LOXs, soybean lipoxygenase (SLO) from plants and human epithelial 15-lipoxygenase-2 (15-LOX-2) from mammals, are described as examples.

Application of Silk Light Chain on a Graphene Composite Surface: A Molecular Dynamics and Electrochemical Experiment.

The surface functionalization of pristine graphene (PG) with beneficial biocomposites is important for biomedical and tissue engineering. This study introduces silk light chain as novel biocomposites to increase the biocompatibility of PG. We explored the supramolecular structures of the silk heavy and light chains. Through molecular dynamics, we compared and analyzed the structural effects and binding mechanisms of these domains in their interaction with PG. Our results highlighted a significant hydrophobic interaction between the silk light chain and PG, without structural collapse. The supramolecular structure of the silk light chain was identified by analyzing the amino acids bound to PG. Moreover, using the silk light chain, the hydrophobic surface of PG has changed to a hydrophilic surface, and the silk light-chain-PG electron transfer rate was evaluated for the graphene congeners: graphene oxide (GO) and reduced graphene oxide. Therefore, we are confident that the dispersibility and biocompatibility of PG can be increased using silk light chains, which will contribute to broadening the field of application of PG-based materials.

Revealing synergistic mechanisms of biochar-assisted microbial electrolysis cells in enhancing the anaerobic digestion performance of waste activated sludge: Extracellular polymeric substances characterization, enzyme activity assay, and multi-omics analysis.

Although biochar (BC)-assisted microbial electrolysis cells (MEC) has been shown to improve anaerobic digestion (AD) performance of waste activated sludge (WAS), the underlying mechanisms remain unclear. This study conducted an in-depth investigation into the mechanism based on analyses of extracellular polymeric substances (EPS) characteristics, enzyme activities and multi-omics. The results showed that compared with the control group, methane production improved by 16.73 %, 21.32 %, and 29.37 % in the BC, MEC, and BC-assisted MEC (BC-MEC) groups, respectively. The reconfiguration of the protein secondary structure increased the hydrophobicity of the EPS, thereby promoting microbial aggregation. In addition, partial least-squares path modeling (PLS-PM) and mantel test based on the enzyme activity and multi-omics analyses revealed that the promotional effect of MEC on the hydrolysis of WAS was superior to that of BC, while BC was more advantageous in promoting electron transfer and biofilm formation regulated by quorum sensing. The synergistic effects of BC and MEC were exemplified in the BC-MEC group. g_norank_Aminicenantales responsible for the hydrolysis of WAS was enriched (29.6 %), and the activities of hydrolytic enzymes including α-glucosidases and proteases were increased by 29.1 % and 43.6 %, respectively. Further, the expressions of genes related to acyl homoserine lactones (AHLs) and diffusible signal factor (DSF) in quorum sensing systems, as well as the genes related to hydrogenase involved in electron transfer (mbhJKL, hyfB-JR, hypA-F, and hoxFHUY), were up-regulated in the BC-MEC group. This facilitated electron transfer and microbial communication, consequently enhancing methane production. This research significantly advances the understanding of the mechanism by which BC-assisted MEC enhances AD performance and provides valuable insights into strategies for improving energy recovery from WAS.

Fe/GMP functional nanomaterial enhancing the denitrification efficiency by bi-signal regulation: Electron transfer and microbial community.

A novel functional nanomaterial composed of guanosine monophosphate (GMP) and Fe enhanced denitrification efficiency by regulating electron transfer and microbial community. Fe/GMP enhanced nitrate (NO3-) degradation rates by 3.00-fold in serum vial batch experiments, with a rate constant of 17.39 mg/(L·h) in sequencing batch reactor. Fe/GMP-mediated interface promoted the secretion of redox-active substances in the extracellular polymeric substances to enhance the extracellular electron transfer. Specifically, Fe/GMP regulated electron transfer and metabolism activity by dynamic conversion of Fe3+/Fe2+ redox signal. Additionally, enzyme activity assays verified the optimized electron distribution function of Fe/GMP and thus enhanced intracellular electron transfer. High-throughput sequencing confirmed Fe/GMP selectively enriched microorganisms (especially Thauera 50.70 %). The tetraethylammonium stress experiment demonstrated Fe/GMP as an exogenous signaling molecule to restore microbial communication for microbial community regulation. The study proposes a multifaceted synergistic mechanism based on the repeater function of Fe/GMP in denitrification and offers insights for practical applications.

Improvement of substrate specificity of the direct electron transfer type FAD-dependent glucose dehydrogenase catalytic subunit.

The heterotrimeric flavin adenine dinucleotide (FAD) dependent glucose dehydrogenase derived from Burkholderia cepacia (BcGDH) has many exceptional features for its use in glucose sensing-including that this enzyme is capable of direct electron transfer with an electrode in its heterotrimeric configuration. However, this enzyme's high catalytic activity towards not only glucose but also galactose presents an engineering challenge. To increase the substrate specificity of this enzyme, it must be engineered to reduce its specificity towards galactose while maintaining its activity towards glucose. To aid in these mutagenesis studies, the crystal structure composed of BcGDH's small subunit and catalytic subunit (BcGDHγα), in complex with D-glucono-1,5-lactone was elucidated and used to construct the three-dimensional model for targeted site-directed mutagenesis. BcGDHγα was then mutated at three different residues, glycine 322, asparagine 474 and asparagine 475.The single mutations that showed the greatest glucose selectivity were combined to create the resulting mutant, α-G322Q-N474S-N475S. The α-G322Q-N474S-N475S mutant and BcGDHγα wild type were then characterized with dye-mediated dehydrogenase activity assays to determine their kinetic parameters. The α-G322Q-N474S-N475S mutant showed more than a 2-fold increase in Vmax towards glucose and this mutant showed a lower activity towards galactose in the physiological range (5mM) of 4.19 U mg-1, as compared to the wild type, 86.6 U mg-1. This resulting increase in specificity lead to an 81.7gal/glc % activity for the wild type while the α-G322Q-N474S-N475S mutant had just 10.9gal/glc % activity at 5mM. While the BcGDHγα wild type has high specificity towards galactose, our engineering α-G322Q-N474S-N475S mutant showed concentration dependent response to glucose and was not affected by galactose.