Extracellular polymeric substances are transient media for microbial extracellular electron transfer

Direct monitoring of electrochemical behavior of viable E. coli under various stress conditions without mediators

Escherichia coli (E. coli) plays a vital role in human life and various fields, yet its naturally non-electroactive nature presents challenges for electrochemical detection. In this study, we directly monitored E. coli's electrochemical behavior in an M9 medium without exogenous electron shuttles or genetic modifications, obtaining an oxidation peak at +0.35 V (vs Ag/AgCl). The electrochemical signal correlated with bacterial growth and viability. Under stress conditions (hypoxia, acid, heat, osmotic, oxidative, and metal ion stress), signal intensity correlates with the number of viable E. coli cells and their electron transport activity. Hydroquinone (HQ) was identified as the contribution to the signal via electrochemical analysis, Prep-HPLC, and GC-MS. This study directs the detection of quinone-related electrochemical behavior in E. coli, offering insights into quinone-mediated electron transfer and potential applications in food science and environmental engineering.

Enhancement of the start-up and performance of an upflow anaerobic sludge blanket (UASB) reactor using electrochemically-enriched biofilm

A novel approach was developed to accelerate the start-up of a 20-L UASB reactor under mesophilic conditions. Two runs were conducted, where the first run (Run I) was inoculated with anaerobic sludge, and the second run (Run II) was inoculated with the same sludge supplemented with enriched electro-active biofilms collected from the working and counter electrodes of anodic and cathodic bio-electrochemical systems (BESs). Reactors' performance and microbial dynamics were monitored over 41 days. Methane production in Run II exceeded 200 mL-CH4/g-COD within 10 days, compared to 29 days in Run I. Run II achieved 80 % removal of soluble COD after 13 days as compared to 23 days in Run I. Sludge washout in Run II stabilized after 3 days, achieving 70 % VSS removal, whereas Run I required 17 days. Greater extracellular polymeric substance (EPS) values and higher protein-to-polysaccharide ratios in Run II may indicate accelerated granules formation mediated by EPS. 16S rRNA gene sequencing analysis results revealed shared genera between both runs but different relative abundances. Methanothrix dominated in Run I, while other archaeal genera, mainly Methanosarcina and Methanobacterium increased in abundance in the Run II. The Enterobacteriaceae family was prevalent in both reactors, with three genera, Citrobacter, Klebsiella, and Enterobacter distinctly dominating at different time points, suggesting potential links with the initial seed sludge or enriched biofilm consortia. The addition of electrochemically grown biofilm in Run II likely enhanced the microbial diversity, contributed to the rapid development of granular syntrophic communities, and improved reactor performance.

Mechanistic insight into enhancement of undissolved rice husk biochar on Tetracycline biodegradation by strain Serratia marcescens basing on electron transfer response

Undissolved biochar (UBC) plays a key role in persistently affecting bacterial characteristics after loss of dissolved biochar. However, its potential role as electron shuttle mediating tetracycline (TC) removal by bacteria is less understood. Result demonstrated UBC (700°C) coupled strain MSM2304 resulted in 72.19 % of TC biodegradation (37.76 % in free cells). UBC improved nutrients usage of TOC and TN to enhance cells proliferation, and facilitated biofilms formation and secretion of redox-active-related extracellular polymeric substances (EPS) including protein (40 % higher) and humus (30 % higher). Moreover, UBC optimized cells oxidative stress indicators including reactive oxygen species (40 % lower), total antioxidant capacity (30 % higher), superoxide dismutase (35 % higher), and catalase (30 % higher) during TC exposure. Importantly, UBC not only accelerated electron transfer from intracellular into extracellular by stimulating cytochrome C reductase activity and cytochrome C development, also decreased extracellular electron transfer resistance between MSM2304 and TC from 231.7 to 109.5 Ω, proved by cyclic voltammetry and electrochemical impedance spectra of EPS, and helped quinone moieties formation on UBC through CO and CC or CO production determined by FTIR and XPS. These findings indicate UBC could be as electron shuttle and contribute to provide a better understanding of interactions between biochar and microorganism.

Sulfur cycle process accelerates microbial fuel cells driven denitrification system: Low sulfate yield and enrichment of functional microorganisms

The denitrification of dual-chamber microbial fuel cells cathodic chamber driven by sulfur powder has the advantages of economy, efficient and pollution-free. However, the low electron utilization of anodic chamber (ACE) and high sulfate (SO42-) production limit its application. Therefore, the cooperation of calcined pyrite (CP) and γ-FeOOH was proposed to solve the above bottleneck problems (S-CP-γ-FeOOH). The results showed that after adding CP and γ-FeOOH to S system, the nitrate removal rate (NRR) changed from 20.39 ± 0.37 % to 94.11 ± 1.40 %; ACE increased from 11.10 ± 0.76 % to 61.05 ± 7.82 %; and SO42- content decreased by 61.26 %. CP and γ-FeOOH promoted the intra/extracellular electron transfer process. SO42- was reduced to sulfur compounds after γ-FeOOH was added, which improved the electron generation efficiency of the anodic chamber. The addition of CP and γ-FeOOH not only enriched sulfur-oxidizing bacteria and enhanced their metabolic activity, but γ-FeOOH also promoted sulfate-reducing bacteria, all of which improved NRR.

Impaired denitrification of aerobic granules in response to micro/nanoplastic stress: Insights from interspecies interactions and electron transfer processes

The accumulation of micro/nanoplastics in wastewater significantly hinders denitrification in biological wastewater treatment systems, yet the intrinsic mechanisms are not fully understood. Herein, we combined signal molecule monitoring, electrochemical characterization and multi-omics analysis to investigate how quorum sensing (QS)-mediated microbial interactions influence denitrification in aerobic granular sludge systems. Results showed that after 90-day exposure to micro/nanoplastics, cross-talk between multiple signal molecules significantly declined, thereby disrupting the QS system to opportunely sense changes in the external environment. As a consequence of impaired QS, only 5 species exhibited up-regulation of the genes encoding amino acids and cofactors to sustain cross-feeding, while others, acting as "cheaters", relied on metabolites offered by cross-feeding but without reciprocating. This imbalance resulted in insufficient availability of metabolites, including redox-active metabolites such as riboflavin, and subsequently deteriorated the denitrification electron transfer process. Compared to the control group, the extracellular electron transfer capacity and denitrification electron transfer chain activity decreased to, respectively, 88.08 % and 63.33 % (microplastics-exposure) and 79.64 % and 63.75 % (nanoplastics-exposure), which directly contributed to the decline in nitrogen removal. Overall, this study provided deeper insights into the denitrification in complex microbial communities under the stress of micro/nanoplastics from the perspective of QS-mediated microbial social behavior.

Unlocking interfacial electron transfer in biophotoelectrochemical processes: Role of extracellular polymeric substances in aquatic environments

The biophotoelectrochemical process (BPECs) integrates the light-absorbing capabilities of nano-semiconductors with the catalytic efficiency of microorganisms, demonstrating significant potential for the development, utilization, transformation, and ecological restoration of water resources. In aquatic environments, extracellular polymeric substances (EPS) serve as a critical interfacial barrier between microorganisms and semiconductor materials, with the underlying electron transfer mechanisms playing a pivotal role in determining the efficiency of bio-photochemical reactions. Despite their importance, the rapidity and complexity of the electron transfer process within EPS pose significant challenges to a comprehensive understanding of BPECs. In this study, an in-situ characterization strategy was employed to rapidly and accurately analyze the components and pathways of photogenerated electron transfer involving EPS at interfaces. The findings indicate that EPS significantly accelerates the transfer of photogenerated electrons within BPECs. Specifically, proteins and redox-active substances within EPS act as efficient conduits for electron transfer, accounting for up to 84.2% of the increased speed in electron transfer rates at bio-abiotic interfaces. Conversely, polysaccharides within EPS impede the electron transfer process but serve as substrates that facilitate methane (CH4) production. The in-situ characterization approach used in this research provides valuable insights into the interfacial electron transfer mechanisms of EPS in BPECs, emphasizing their relevance in aquatic environments. This study establishes a theoretical framework for designing high-performance BPECs, with significant implications for the energy utilization of water resources and the transformation of water pollutants.

Molecular insights into dye decolorization performance and mechanisms under carbon limited conditions in a membrane aeration-based bioelectrochemical system

Bioelectrochemical systems (BES) is a promising strategy for azo dyes decolorization enhancement in carbon-limited condition, but decolorization products need further aerobic mineralization. Here, a counter-diffusion biofilm-supported BES (E-MABR) was designed to achieve the decolorization, mineralization and denitrogenation of Alizarin Yellow R (AYR) in electron-deficient wastewater. The introduction of electrodes facilitated the secretion of extracellular polymeric substances (EPS), particularly proteins (PN), whose content in the cathodic biofilm was 2.5 ± 0.2 times higher than that in the MABR. Additionally, electrical stimulation enriched electroactivity bacteria (e.g. Geobacter) and azo dyes metabolism contributor (e.g., Thauera and Dechloromonas), and significantly upregulated the expression of decolorization-related genes, particularly azoR (1.2 log2) in the cathodic biofilm. The increased β-sheet proportions of protein structures in the anode (22.2 ± 1.5 %) and cathode (20.1 ± 1.7 %) promoted the exposure of hydrophobic groups in amino acid; consequently, more hydrogen bonds formed, leading to stronger hydrophobic interactions in molecular dynamic simulations. Under the electric field stress, the total binding free energy between azoR and AYR declined to -32.6 kJ·mol⁻¹, enhancing the stability of the complex and creating a favourable environment for AYR degradation. Finally, under carbon-limiting conditions, E-MABR significantly promoted AYR decolorization efficiency, mineralization efficiency, and total nitrogen removal by 32.4 ± 2.3 %, 29.4 ± 3.6 %, and 18.4 ± 2.0 %, respectively, compared to MABR.

Sulfate reducing bacteria corrosion of a 90/10 Cu-Ni alloy coupled to an Al sacrificial anode

This study investigates the corrosion of 90/10 copper-nickel (Cu-Ni) alloy caused by sulfate-reducing bacteria (SRB) in the presence of aluminum anodes, with particular emphasis on the role of electron supply in microbial corrosion and the resulting local corrosion failures. The study reveals that the electron supply from the anode supports SRB growth on the Cu-Ni alloy through an "Electrons-siphoning" mechanism. However, the supply is insufficient to sustain the SRB population, resulting in ineffective cathodic protection (icorr = 2.34 × 10-6 A cm-2). The addition of 20 ppm riboflavin (RF) to the SRB biofilm enhances electrical activity and increases the electron donor density, thereby restoring the anode's protective effect. As a result, the icorr of the 90/10 Cu-Ni alloy decreases by an order of magnitude (to 3.5 × 10-7 A cm-2). These findings provide valuable new insights into the mechanisms of microbial corrosion.

Synthetic microbial community maintains the functional stability of aerobic denitrification under environmental disturbances: Insight into the mechanism of interspecific division of labor

Understanding how synthetic microbial community (SMC) respond to environmental disturbances is the key to realizing SMC engineering applications. Here, dibutyl phthalate (DBP) and levofloxacin (LOFX) were used as environmental disturbances to study their effects on the aerobic denitrification functional stability of SMC composed of Pseudomonas aeruginosa N2 (PA), Acinetobacter baumannii N1(AC) and Aeromonas hydrophila (AH). The results showed that aerobic denitrification efficiency could be maintained at about 93 % under DBP or LOFX disturbance, and interspecific communication was mainly carried out through N-butyryl-L-homoserine lactone (C4-HSL) and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), correspondingly. DBP and LOFX induced the acceleration of tricarboxylic acid (TCA) cycle, which facilitated the energy flux and extracellular polymeric substances (EPS) production, thereby allowing SMC to adapt to disturbances. Under DBP disturbance, DBP stimulated phenazine-1-carboxylic acid production to accelerate electron transfer from the quinone pool to complex III, resulting in an increase in electron transfer activity. Up-regulation of complex I, complex III and heme synthesis genes under LOFX disturbance led to enhanced denitrification enzymes expression and electron transfer efficiency. SMC re-regulated different metabolic pathways to build metabolic networks to maintain normal metabolic activity under different disturbances. Overall, SMC maintained functional stability through the labor division in modulation of interspecific communication, formation of defensive barriers, promotion of energy flux, directional transfer of electron flux, and reconstruction of metabolic networks. DBP stimulated AH and PA to occupy functional dominance, while LOFX induced AC and PA to play a major role. The understanding of the stability mechanism under different environmental disturbances provides valuable guidance for stability maintenance and engineering applications of SMC.

Decoy EPS layers for trapping and killing bacteria

Here we report a novel strategy using bacterial extracellular polymeric substances (EPS) as decoys to enhance bacterial adhesion and contact-based antimicrobial activity. EPS extracted from Staphylococcus aureus and Bacillus subtilis was used to coat wafers as a conditioning layer to alter surface properties and facilitate bacterial aggregation. Results show that EPS downregulates quorum sensing-related genes (agr and atl in Staphylococcus aureus by 80.5 % and 86.6 %, respectively; fliC in Escherichia coli by ~58.3 %), suggesting that EPS facilitates energy-efficient adhesion independent of quorum sensing signals. Loading antibiotics (erythromycin, linezolid, levofloxacin) into the EPS layer further enhances adhesion and contact killing. Especially, the surfaces loaded with a levofloxacin concentration of 2 μg/mL exhibit a significant antimicrobial effect. For Staphylococcus aureus, the antimicrobial rate reaches 83.66 % after 4 h incubation but drops to 39.9 % after 8 h incubation. In contract, Escherichia coli exhibits greater sensitivity, with antibacterial activity increasing to 92.97 % after 8 h incubation. Laser confocal microscopy characterization further reveals that the antibiotic-loaded EPS surfaces possess remarkable contact bacteria-killing activity. Our results show the promising recruiting-killing efficacy of the antibiotics-loaded EPS against bacteria, which would give insight into exploring new antibacterial strategies for enhanced contact-antibacterial performances.

The impact of microplastics and nanoplastics on biological nitrogen removal processes: Exacerbating the greenhouse effect

The widespread presence of microplastics/nanoplastics (MPs/NPs) in various environments poses a significant threat to the ecological environment. Wastewater treatment plants (WWTPs) serve as significant reservoirs of MPs/NPs, wherein a substantial quantity of these are adsorbed by activated sludge in the biological treatment system and continuously accumulated, thereby jeopardizing the stable operation of biological nitrogen removal (BNR) processes. Consequently, it is imperative to comprehensively summarize the impacts of MPs/NPs on BNR process performance and elucidate their underlying mechanisms of action. This review paper provides an overview of the sources and types of MPs/NPs found in WWTPs, examines their effects on different BNR processes, and summarizes several inhibition mechanisms associated with MPs/NPs exposure. The findings indicate that the inhibitory effect exerted by MPs/NPs on BNR processes is closely correlated with their polymer type, size, concentration, and duration of exposure. Anaerobic ammonium oxidation processes exhibit higher sensitivity towards MP/NP exposure. Furthermore, analysis reveals that MPs/NPs influence microbial activity through protein secretion inhibition, competition for substrate adsorption sites, obstruction of substrate transport channels, attenuation of extracellular electron transfer processes, and induction of reactive oxygen species production. Additionally, MPs/NPs will expedite the migration of toxic and deleterious substances, such as heavy metals and antibiotics, towards microbes. Finally, molecular docking simulation experiments demonstrate that PS-MPs exhibit superior binding energy with key enzymes involved in nitrogen removal functionality. Nor functional enzymes display high binding energy levels when interacting with diverse types of MPs. The presence of MPs/NPs leads to accumulation of NO and N2O, greatly exacerbating the greenhouse effect. The article offers new insights into the impact of MPs/NPs on BNR process and lays the groundwork for developing strategies to mitigate this impact.

Construction of immobilized functional microflora system and research on mechanism of enhanced degradation of aromatic compounds in coal chemical wastewater

Aiming to address the practical challenges of aromatic compound degradation in the biochemical treatment system of coal chemical wastewater (CCW), this study constructed an immobilized functional microflora system using modified zeolite as a bacterial carrier. The study evaluated the system's continuous efficacy in degrading aromatic compounds and explored the underlying mechanisms of the immobilized microflora system in enhancing degradation. The findings demonstrated that zeolite material modified by calcination at 300 °C exhibited the highest immobilization capacity for the microflora, achieving a microorganism immobilization amount of 0.81 mg/g. Additionally, when the chemical oxygen demand (COD) concentration stabilized at 1250 ± 20 mg/L, COD removal was maintained steadily above 65 %. The removal efficiencies for phenols and polycyclic aromatic hydrocarbons were 76.85 % and 52.52 %, respectively, representing enhancements of 19.17 % and 23.15 % compared to the control group (activated sludge alone). The secretion characteristics of microbial extracellular polymeric substances and the variation in protein secondary structure and hydrogen bonding structure were further analyzed. The results indicated enhanced secretion of the protein and the polysaccharide, an increased α-helix to (β-sheet + random coil) ratio, and stronger intermolecular hydrogen bonding. These findings suggest that the immobilized microflora system improved microbial adaptability to environmental stress. Additionally, increased expression of key enzymes such as Dehydrogenase, Catechol 1,2-dioxygenase, and Catechol 2,3-dioxygenase, alongside enhanced levels of dominant bacteria like Candidatus_Competibacter, Luteococcus and Flavobacterium underscored the critical role of immobilized functional genera in the degradation of aromatic compounds. The results of the study are of great practical significance for the regulation of the operation stability of the biochemical treatment system of CCW and the realization of the completely harmless treatment of CCW.

Utilization of the liquid one carbon feedstocks methanol and formate for acetogenic bioproduction of chemicals and fuels

The fight against climate change requires consideration of carbon as a critical parameter in production systems, with the ultimate aim of creating a truly sustainable circular carbon economy. In this context, microbial bioproduction systems are a promising route to renewably generate value-added chemicals and fuels. Methanol and formate have recently gained interest as microbial one-carbon feedstocks, which can be produced sustainably from carbon dioxide and renewable energy, are easy to store and transport and readily dissolve in aqueous solutions. Acetogenic bacteria are strictly anaerobic microorganisms that can grow autotrophically on molecular hydrogen or use methanol, formate, and carbon monoxide as their sole carbon and energy sources via the Wood-Ljungdahl pathway, the most energetically efficient carbon fixation pathway known to date. Here, known variants of the Wood-Ljungdahl pathway, the physiology of a selection of methylotrophic and formatotrophic acetogens, and emphasize recent advancements in bioprocessing with respect to quantification of acetogen metabolism of methanol and formate as well as research aiming at establishing novel bioprocesses are reviewed. Additionally, the tools available for physiological and metabolic studies as well as for metabolic and genetic engineering are discussed. Finally, the features and constraints that govern the bioenergetics and stoichiometry of acetogen metabolism during growth on methanol and formate are reviewed, and future perspectives of the field discussed. The high energetic efficiency with which acetogens can convert methanol and formate into products renders them highly attractive platform hosts in the circular carbon economy.

Non-Respiratory Extracellular Electron Transfer Competes with Nitrogenase for Electrons in Rhodopseudomonas Palustris

Biological nitrogen fixation (BNF) is a pivotal process that reduces nitrogen to ammonium within the nitrogen cycle. Extracellular electron transfer (EET) between diazotrophs and the extracellular environment influences the occurrence and efficiency of BNF. Although extracellular electron acceptors can function as a component of the electron transport chain, providing energy for chemotrophic nitrogen fixation via extracellular respiration, the function and mechanism of outward EET in photosynthetic diazotrophs remain unclear. Here, using Rhodopseudomonas palustris TIE-1, a photosynthetic bioelectrochemical nitrogen fixation system is established for simultaneous nitrogen fixation and current generation, to dissect the complex interaction between these two processes. Outward EET functions are found to maintain redox balance, rather than serving as an extracellular respiration pathway. It significantly suppresses BNF by competing with nitrogenase for electrons. Lumichrome serves as the primary electron shuttle for indirect electron transfer, while cytochromes play an important role in direct electron transfer. Notably, the pio operon participates in outward EET. This study reveals the interaction mechanism between photosynthetic BNF and outward EET, providing new insight into the regulatory mechanisms of nitrogen fixation in anoxygenic phototrophs across diverse environmental conditions.

Metagenomic insights into the response of microbial metabolic function and extracellular polymeric substances from microalgae-bacteria consortia to fluoroquinolone antibiotics

Microalgae-bacteria consortia (MBC) are considered a promising bioremediation technology for removing pollutants from swine wastewater. However, the overuse of antibiotics poses challenges to the effective functioning of MBC. In this study, the removal efficiency of nutrients in wastewater by MBC under different antibiotic concentrations (0, 1, 5, 10 and 50 mg/L) was evaluated. The changes of functional microbial abundance were elucidated and the response mechanism of MBC against antibiotics was investigated. Antibiotics inhibited the accumulation of MBC biomass and reduced the removal efficiency of ammonia nitrogen and total phosphorus in wastewater by 8.39 % and 8.74 % respectively. In addition, antibiotics affected the relative abundance of microorganisms (Raineyella, from 30.72 % to 15.96 %) and functional genes (glnA, gudB, NirK, NirBD, NarB, NapAB, NorBC and NosZEPS) involved in N metabolism. MBC could defend against the adverse effects of antibiotics by regulating the content of proteins in the extracellular polymeric substances.

Enhanced activity of mixed-culture electroactive biofilms and sulfamethoxazole removal efficiency by adding N-acyl-homoserine lactones in bio-electrochemical system

The addition of exogenous quorum sensing signaling molecules significantly enhanced the degradation efficiency of antibiotics, such as chloramphenicol in bio-electrochemical systems (BESs). However, the effects and mechanisms by which AHLs addition in BES facilitated the removal of sulfamethoxazole (SMX) remained inadequately explored. This study systematically compared the electrochemical performance and SMX removal efficiency in BES under two conditions: with and without the addition of N-acyl-homoserine lactones (AHLs) signaling molecules. In comparison to the control group, the AHL-treated group exhibited an increase in maximum output voltage from 340 to 489.67 mV, alongside a notable enhancement in SMX removal efficiency over 120 h ranging from 14.65% to 15.76%. Analyses of the live and dead cells and extracellular polymeric substances (EPS) composition revealed that following AHLs addition, both the ratio of live to dead cells and protein content within EPS increased by 12.66% and 74.37%, respectively. Furthermore, microbial community structure analysis indicated that after AHLs supplementation, there was a marked increase in the abundance of electroactive microorganisms as well as antibiotic-degrading and nitrogen-removing bacteria. Notably, Klebsiella - characterised by its electroactivity along with antibiotic degradation and nitrogen removal capabilities - exhibited a relative abundance reaching 56.84% in AHL, reflecting an increase of 28.31% compared to Blank; additionally, electroactive bacteria Dysgonomonas showed a relative abundance rise of 2.49%. Collectively, these findings suggested that enhancements in SMX removal efficiency upon AHLs addition were primarily driven by improvements in electrochemical performance coupled with alterations in microbial community structure.Highlights The electrochemical performance in AHL was improved compared with Blank.The protein content in extracellular polymeric substances increased by 74.37% in AHL.The removal efficiency of sulfamethoxazole in 120 h increased by up to 15.76% in AHL.The abundance of functional bacteria such as Klebsiella increased in AHL.

Tracing the electron transfer behavior driven by hydrophyte-derived carbon materials empowered autotrophic denitrification in iron-based constructed wetlands: Efficacy and enhancement mechanism

Iron-based constructed wetlands (ICWs) displayed great potential in deep nitrogen elimination for low-polluted wastewater. However, the unsatisfactory denitrification performance caused by the limited solubility and sluggish activity of iron substrates needs to be improved in an eco-effective manner. To fill this gap, the bioavailability of iron substrates (iron scraps) affected by wetland biomass-derived carbon materials with potential conductivity were explored. Results indicated that the cumulative removal of TN in biochar-added ICW (BC-ICW) and activated carbon-added ICW (AC-ICW) increased by 29.04 % and 22.96 %, respectively. The carbon matrix of AC played the geo-conductor role to facilitate the rapid release of iron ions, as indicated by the higher TN removal efficiency of AC-ICW (45.36 ± 1.45 %) at the early stage, while the reduced conductivity of AC negatively impacted the nitrogen removal. BC-ICW exhibited intensified denitrification potential, with higher TN removal capacity (52.08 ± 3.04 %) and effluent Fe2+ concentration. Electroactive bacteria (EB) (Geobacter, Desulfovibrio, Shewanella, etc.) associated with extracellular electron transfer were enriched in BC-ICW, as well as the expanded niches breadth and improved microbial community diversity. The electron-shuttling effect of BC was mainly attributed to its oxygenated functional groups (quinone/phenolic moieties), which supported the electron transfer from EB to extracellular iron oxides, as evidenced by the increased Fe(III)(hydro)oxides bioavailability. Besides, biochar concurrently up-regulated the gene expression of electron transport chains/mediators and denitrification reductases, suggesting that BC boosted the active iron cycle and iron-mediated autotrophic denitrification in ICWs by accelerating intracellular and extracellular electron transfer. This work explored the electron transfer behavior of biomass-derived carbon materials coupled with ICWs to enhance denitrification, providing insights into the sustainable application of biomass derived carbon-assisted ICWs in tertiary treatment.

Deciphering the synergistic effects and mechanisms of biochar and magnetite contained in magnetic biochar for enhancing methane production in anaerobic digestion of waste activated sludge

Adding conductive materials is one of the most extensive enhancement strategies while treating waste activated sludge via anaerobic digestion. Magnetic biochar (MBC), as one composite conductive material, is capable of enhancing methane yield and production rate because of its favorable characteristics. However, whether the synergistic effects formed or not between biochar and magnetite contained in MBC on anaerobic digestion is still unclear. This study investigated the synergistic effects and corresponded mechanisms of biochar and magnetite contained in MBC with semi-continuous anaerobic digestion mode. Results showed that the co-addition of biochar and magnetite performed non-synergistic effects on methane production potential, with decrease ratios of 2.2 % and 7.4 % respectively compared to that in biochar and magnetite groups. Interestingly, the biochar and magnetite contained in MBC formed synergistic effects, with an extra improvement of 5.5 % compared to the sum of those obtained in biochar and magnetite groups. The synergistic effects came from efficient hydrolysis and acidogenesis stages, including the thorough degradation of soluble organic matters and the rapid conversion of acetic acids. MBC also produced synergistic effects on the hydrophilia and redox properties of extracellular polymeric substances, the activities of enzymes involved in interspecies electron transfer, and the contents of adenosine triphosphate (ATP). Specifically, the enhancement potential contributed by MBC exceeded the total enhancement potential contributed by biochar and magnetite, with the extra enhancement ratios of 13.1 % and 19.4 % for cytochrome c and ATP, thus, the biochar and magnetite contained in MBC formed synergistic effects for promoting electron transmembrane and transfer from kinetic aspects. The correlation coefficient between methane production performance and the microbial electron transfer activity reached 0.96, correspondingly, the highest electron transfer activity of microorganisms was presented in MBC. As for microbial communities, the functional and electro-active microorganisms were enriched with the addition of MBC, such as Peptoclostridium, Anaerolineaceae, Methanosarcina, and Methanosaeta, which facilitated the conversion of organic matters and established direct interspecies electron transfer methanogenesis. The findings of this study revealed the synergistic effects and mechanisms of biochar and magnetite contained in magnetic biochar in enhancing sludge anaerobic digestion, and provided an effective strategy to recover bioenergy from waste activated sludge, potentially boosting carbon neutrality in wastewater treatment.

Polythiophene-Based Nonmetal Electrocatalyst with Biocompatibility to Boost Efficient CO2 Conversion

In a hybrid microbial-inorganic catalysis system, H2 evolution reaction (HER) electrocatalysts are coupled with microorganisms to achieve the highly efficient conversion of CO2 to value-added chemicals using H2 as an electron mediator. However, currently developed HER electrocatalysts suffer from poor biocompatibility, hindering the performance of the system. This study presents a N- and Si-doped polythiophene nanocomposite (PTh-NSi) as a nonmetal HER electrocatalyst with biocompatibility for use in a hybrid microbial-inorganic catalysis system. By coupling PTh-NSi with Ralstonia eutropha H16, conversion of CO2 to poly-β-hydroxybutyrate with a maximum yield of 662.99 ± 27.46 mg/L was achieved. The PTh-NSi electrocatalyst demonstrated HER performance in bacterial media, minimal reactive oxygen species production, and no heavy metal ion leaching, ensuring biocompatibility with R. eutropha H16. The interactions between PTh-NSi and R. eutropha H16 were revealed. This work highlights an approach to designing biocompatible catalysts for hybrid microbial-inorganic catalysis systems, offering the potential for sustainable CO2 conversion.

Recyclable cation exchange resin-driven fermentation of waste activated sludge in sequential batch-parallel pattern: long-term resin/regenerant recycle stability and triple driving mechanisms

Anaerobic acidogenic fermentation has been posited as a preferable technology for waste activated sludge management, whereas the inefficient hydrolysis, inadequate metabolism and disordered microbiota still existed as three fermentability limitations. The existing solutions addressed single limitation while consuming substantial chemicals/energy, thereby restraining technological dissemination. Innovatively, the recyclable cation exchange resin (CER) is a promising approach for synchronously overcoming these fermentability limitations and reducing chemicals/energy costs from sludge-native metal removal perspective; however, it has been rarely reported. This study pioneered a recyclable CER-driven sludge fermentation in continuous CER and regenerant reuse scene, taking comprehensive insights into long-term performance and multiple mechanisms. The CER induced speciation conversion and stepwise removal of structural metals from sludge, especially organic-binding and residual Ca&Mg, which played triple driving contributions: (1) breaking metal-bridging sites and hydrogen bonds disentangled protein molecules for raising electronegative repulsion and flocculation energy barrier, causing synergic extracellular and intracellular hydrolysis (up to 30.05 %); (2) liberating endogenous redox mediators from metal-complexations for assisting electron shuttle and extracellular respiration, which metabolic electron transfer activity by 1.58 times; (3) triggering "bacteria screening" through sensitive methanogen inhibition and tolerant acidogens growth towards maximum acidogenic eco-functions. Such fermentability breakthroughs greatly promoted short-chain fatty acids (superior carbon sources) accumulation by average 2.52 folds while declining sludge solid by 55.87 %. The NaCl regeneration thoroughly restored CER active sites and eluted pollutant blockages, with negligible capability loss ≤ 3.53 % in 18-cycle operations, which stabilized acidogenic performances during 72-day fermentation (RSD ≤ 7.88 %). The fermentative products presented as high-quality carbon sources with abundant carbon and absent nitrogen, owing to CER-mediated NH4+ exchange. Innovative batch-parallel operation was established in engineering strategy, offering 409.49 CNY/ton SS income. The findings provided mechanism framework linking sludge fermentability with native metal functions.

Enhancing sulfide mitigation via the synergistic dosing of calcium peroxide and ferrous ions in gravity sewers: Efficiency and mechanism

Chemical dosing constitutes an effective strategy for sulfide control in sewers; however, its efficacy requires further optimization and enhancement. In this study, a novel dosing strategy using the synergistic dosing of calcium peroxide (CaO2) and ferrous ions (Fe2+) for sulfide control was proposed, and its efficacy in controlling sulfides was evaluated using a long-term laboratory-scale reactor. The results showed that adding CaO2-Fe2+ improves the effect of sulfide control. When the ratio of the agent to the sewage (w/v) was 0.30 %, the RT50 of sulfide production rate was 8.34 days. The analysis of microbial communities in sewage biofilm revealed that the relative abundances of sulfate-reducing bacteria (SRB) and sulfide-oxidizing bacteria (SOB) demonstrated an overall downward tendency, suggesting that the potent oxidizing •OH generated by the synergism of CaO2 and Fe2+ could indiscriminately restrain the growth of microorganisms. Additionally, intracellular metabolic pathways, along with enzyme activities and the relative abundances of genes associated with sulfide metabolism, were significantly impaired. The cost of CaO2-Fe2+ synergistic dosing is 31.3 % of CaO2 and 63.4 % of Fe2+ alone addition. It can be reasonably proposed that the addition of CaO2-Fe2+ may provide an efficacious and cost-effective method for the mitigation of sulfide in sewer systems.

In-situ synthesis of FeS nanoparticles enhances Sulfamethoxazole degradation via accelerated electron transfer in anaerobic bacterial communities

The impact of nanominerals on microbial electron transfer and energy metabolism strategies during pollutant degradation remains uncertain. This study used in situ synthesized FeS nanoparticles (FeS NPs) to increase the degradation efficiency of SMX by anaerobic bacterial communities from 25.80 % to 47.60 %. The proportion of intracellular degradation by bacteria in the community significantly increased by 23.25 times, which mainly facilitated by NADH-dependent reductases and iron-sulfur proteins. Microbial network analysis and electrochemical analysis indicated that the in-situ synthesis of FeS NPs altered the interactions among different microbial species, enabling Petrimonas to transfer electrons directly to Lysinibacillus more effectively. This adjustment led to an increase in the activity of the electron transport system by 1.2 times, an increase in the electron supply capacity by 2.8 times, and a decrease in the electrochemical impedance (EIS) to 3.21 Ω. Moreover, the coupling of electron transfer pathways and protease transport channels significantly increased Na+/K+-ATPase by 14.72 times. Inhibitor experiments and molecular dynamics (MD) results showed that FeS NPs interact with Nqo1 in the cell membrane via electrostatic force at -28.573 kcal/mol, forming a unique electron conduit with ubiquinone (CoQ). This study provides new insights into the role of in situ nanominerals in electron transfer between different microorganisms, aim to enhance the antibiotic wastewater treatment efficiency in actual anaerobic processes.

Insights into the enhanced uranium reduction efficiency through extracellular polymeric substances from Desulfovibrio vulgaris UR1 induced by mediating materials

Understanding the role of extracellular polymeric substances (EPS) in the microbial reduction of uranium accelerated by mediating materials is crucial for enhancing the bioremediation of uranium-contaminated wastewater. In this study, biochar- and magnetite-loaded Desulfovibrio vulgaris UR1 exhibited significantly higher uranium reduction efficiency, with increases of 1.52 and 1.44 times respectively within one day. After loading with mediating materials, the charge transfer resistance of EPS was reduced, facilitating the extracellular electron transfer process. The increase of redox components, such as aromatic compounds and flavins, in EPS explained the enhanced extracellular electron transfer capacity. Moreover, the higher α-helix content in extracellular proteins could promote electron hopping. Proteomics analysis showed that extracellular proteins involved in iron-sulfur cluster binding, oxidoreductase activity, and electron transfer were significantly up-regulated, which facilitated the rapid microbial reduction of uranium. These findings provide valuable insights into the in-depth development of bioremediation technology for uranium-contaminated wastewater.

Extracellular electron transfer-dependent bioremediation of uranium-contaminated groundwater: Advancements and challenges

Efficient and sustainable remediation of uranium-contaminated groundwater is critical for groundwater safety and the sustainable development of nuclear energy, particularly in the context of global carbon neutrality goals. This review explores the potential of microbial reduction processes that utilize extracellular electron transfer (EET) to convert soluble uranium (U(VI)) into its insoluble form (U(IV)), presenting a promising approach to groundwater remediation. The review first outlines the key processes and factors influencing the effectiveness of dissimilatory metal-reducing bacteria (DMRB), such as Geobacter and Shewanella, during uranium bioremediation and recovery. The cutting-edge progress on the molecular mechanism of EET-driven U(VI) reduction mediated by c-type cytochromes, conductive pili, and electron mediators, is critically reviewed. Additionally, advanced strategies such as optimizing electron transfer, leveraging synthetic biology approach, and integration with machine learning are discussed to enhance the efficiency of EET-driven processes. The review also considers the integration of EET processes into practical engineering applications, highlighting the need for optimization and innovation in bioremediation technologies. By providing a comprehensive overview of current progress and challenges, this review aims to inspire novel research and practical advancements in the field of uranium-contaminated groundwater remediation.

The Role of Anode Potential in Electromicrobiology

Electroactive microorganisms are capable of exchanging electrons with electrodes and thus have potential applications in many fields, including bioenergy production, microbial electrochemical synthesis of chemicals, environmental protection, and microbial electrochemical sensors. Due to the limitations of low electron transfer efficiency and poor stability, the application of electroactive microorganisms in industry is still confronted with significant challenges. In recent years, many studies have demonstrated that modulating anode potential is one of the effective strategies to enhance electron transfer efficiency. In this review, we have summarized approximately 100 relevant studies sourced from PubMed and Web of Science over the past two decades. We present the classification of electroactive microorganisms and their electron transfer mechanisms and elucidate the impact of anode potential on the bioelectricity behavior and physiology of electroactive microorganisms. Our review provides a scientific basis for researchers, especially those who are new to this field, to choose suitable anode potential conditions for practical applications to optimize the electron transfer efficiency of electroactive microorganisms, thus contributing to the application of electroactive microorganisms in industry.

The removal of high Se(IV) and Cd(II) concentrations in sulfur autotrophic reactor based on the "hibernation-like microbial survival strategy"

The removal of selenite (Se(IV)) and cadmium (Cd(II)) from low-carbon wastewater presents significant challenges. However, the addition of external organic carbon sources is limited in application due to the high cost and potential for secondary pollution. This study introduced a "hibernation-like microbial survival strategy", enabling efficient removal of Se(IV) and Cd(II) in sulfur autotrophic reactor, with S0 acting as the electron donor. The removal efficiencies of 5-120 mg/L Se(IV) and 50 mg/L Cd(II) were higher than 99 % in phase I-IV, and the nanoparticles formed in sulfur autotrophic reactor were available for recycling. The analysis of X-ray photoelectron spectroscopy confirmed that the removal pathways of Se(IV) and Cd(II) were biological reduction, adsorption, and biosynthesis. The decreased ratio of actual to theoretical sulfate concentrations indicated the weakened sulfur disproportionation trend in sulfur autotrophic reactor. The formation of autotrophic-heterotrophic symbiont was beneficial for promoting electron transfer, material exchange, and information flow. Microorganisms strategically decreased metabolic activity to reduce extra energy consumption under Se(IV) and Cd(II) stress, which was manifested in the decreased extracellular DNA, extracellular polymeric substances, and electron transfer system activity. Furthermore, microorganisms reduced the secretion of nicotinamide adenine dinucleotide, cytochrome c, and cyt-c oxidase on the premise of ensuring the required electron flux. The "hibernation-like microbial survival strategy" was proposed to explain the removal of Se(IV) and Cd(II) in sulfur autotrophic reactor, expanding the potential application of sulfur autotrophy in environmental engineering.

Evaluating advancements and opportunities in electro-assisted biodehalogenation of emerging halogenated contaminants

Electro-assisted biodehalogenation (EASB) as a biostimulation strategy can accelerate the slow attenuation of emerging halogenated contaminants (EHCs) in anaerobic aqueous environments. A timely review is urgent to evaluate the knowledge gaps and potential opportunities, further facilitating its design and application. Till now, EASB achieves promising progress in accelerating biohalogenation rates, promoting the detoxification of EHCs to cope with unfavourable environments and mitigating greenhouse gas emissions. However, EASB of EHCs still faces several knowledge gaps. Exploring crucial microbes and deciphering insights into dehalogenase characteristics and extracellular electron transfer (EET) pathways remain the prominent task for EASB of EHCs. Moreover, microbial ecological relationships and intricate environmental factors affecting performances and applications are largely underexplored. The emergence of emerging tools holds promises for sorting the intricate changes and addressing these knowledge gaps. Judicious use of emerging tools will rejuvenate EASB strategy, from EET to scale-up, to purposefully and effectively address cascading EHCs.

Piezoelectric Biomaterial with Advanced Design for Tissue Infection Repair

Bacterial infection has become the most dangerous factor in tissue repair, which strongly affects the tissue regeneration efficiency and wellness of patients. Piezoelectric materials exhibit the outstanding advantage of producing electrons without external power supply. The ability of electron enrichment and reactive oxygen species generation through noninvasive stimulations enables piezoelectric materials the potential applications of antibacterial. Many studies have proved the feasibility of piezoelectric materials as a functional addition in antibacterial biomaterial. In fact, numerous piezoelectric materials with ingenious designs are reported to be effective in antibacterial processes. This review summarizes the antibacterial mechanisms of piezoelectric, illuminating their potential in combating bacteria. Recent advancement in the design and construction of piezoelectric biomaterial including defect engineering, heterojunction, synergy with metal and the composite scaffold configuration are thoroughly reviewed. Moreover, the applications and therapeutic effects of piezoelectric materials in common tissues with antibacterial requirements are introduced, such as orthopedics, dental, and wound healing. Finally, the development prospects and points deserving further exploration are listed. This review is expected to provide valuable insight into the relationship between antibacterial processes and piezoelectric materials, further inspiring constructive development in this emerging scientific discipline.

Engineering Exopolysaccharide Biosynthesis of Shewanella oneidensis to Promote Electroactive Biofilm Formation for Liquor Wastewater Treatment

Microbial electrochemical systems (MESs), as a green and sustainable technology, can decompose organics in wastewater to recover bioelectricity. Electroactive biofilms, a microbial community structure encased in a self-produced matrix, play a decisive role in determining the efficiency of MESs. However, as an essential component of the biofilm matrix, the role of exopolysaccharides in electroactive biofilm formation and their influence on extracellular electron transfer (EET) have been rarely studied. Herein, to explore the effects of exopolysaccharides on biofilm formation and EET rate, we first inhibited the key genes responsible for exopolysaccharide biosynthesis (namely, so_3171, so_3172, so_3177, and so_3178) by using antisense RNA in Shewanella oneidensis MR-1. Then, to explore the underlying mechanisms why inhibition of exopolysaccharide synthesis could enhance biofilm formation and promote the EET rate, we characterized cell physiology and electrophysiology. The results showed inhibition of exopolysaccharide biosynthesis not only altered cell surface hydrophobicity and promoted intercellular adhesion and aggregation, but also increased biosynthesis of c-type cytochromes and decreased interfacial resistance, thus promoting electroactive biofilm formation and improving the EET rate of S. oneidensis. Lastly, to evaluate and intensify the capability of exopolysaccharide-reduced strains in harvesting electrical energy from actual liquor wastewater, engineered strain Δ3171-as3177 was further constructed to treat an actual thin stillage. The results showed that the output power density reached 380.98 mW m-2, 11.1-fold higher than that of WT strain, which exhibited excellent capability of harvesting electricity from actual liquor wastewater. This study sheds light on the underlying mechanism of how inhibition of exopolysaccharides impacts electroactive biofilm formation and EET rate, which suggested that regulating exopolysaccharide biosynthesis is a promising avenue for increasing the EET rate.

Metagenomic insight into the diffusion signal factor mediated social traits of anammox consortia after starvation

Biomass starvation is common in biological wastewater treatment. As a social trait of microbial community, how quorum sensing (QS) regulated bacterial trade-off through interactions after starvation remains unclear. This study deciphered the mechanism of anaerobic ammonium oxidation (anammox) consortia in response to starvation, including reducing extracellular electron transfer (EET), adenosine 5'-triphosphate (ATP) content and amino acid metabolism. Metagenomic analysis has shown that the addition of the diffusion signal factor (DSF) resulted in a high abundance of antioxidant genes, which contributed to achieving redox balance in anammox bacteria. There was an enrichment of Geobacter and Methanosarcina, which were QS-responsive direct interspecific electron transfer participants. Furthermore, DSF stimulated the nitrogen and carbon metabolism of Ca. Kuenenia_stuttgartiensis, promoting syntrophy of metabolic intermediates within microbial community. This study highlighted the effect of DSF on the microbial interaction patterns and deciphered the QS-based social traits of anammox consortia after starvation, facilitating the stable operation of the anammox process.

Microbial extracellular polymeric substances in the environment, technology and medicine

Microbial biofilms exhibit a self-produced matrix of extracellular polymeric substances (EPS), including polysaccharides, proteins, extracellular DNA and lipids. EPS promote interactions of the biofilm with other cells and sorption of organics, metals and chemical pollutants, and they facilitate cell adhesion at interfaces and ensure matrix cohesion. EPS have roles in various natural environments, such as soils, sediments and marine habitats. In addition, EPS are relevant in technical environments, such as wastewater and drinking water treatment facilities, and water distribution systems, and they contribute to biofouling and microbially influenced corrosion. In medicine, EPS protect pathogens within the biofilm against the host immune system and antimicrobials, and emerging evidence suggests that EPS can represent potential virulence factors. By contrast, EPS yield a wide range of valuable products that include their role in self-repairing concrete. In this Review, we aim to explore EPS as a functional unit of biofilms in the environment, in technology and in medicine.

Integration of manganese ores with activated carbon into constructed wetland for greenhouse gas emissions reduction

Manganese oxide and activated carbon (AC) are widely employed in constructed wetlands (CWs) to remove nutrients and reduce greenhouse gas (GHG) emissions, however, the effect and mechanism of AC combined with manganese ores (MO) on GHG emissions remain unclear. In this study, the mechanisms of nutrient removal and GHG emissions reduction were investigated by three vertical subsurface-flow CWs: gravel (CW-B), manganese ores (MO) uniformly mixing with gravel (CW-M), or activated carbon (CW-MC). The average removal efficiencies of chemical oxygen demand, total nitrogen and total phosphorus in CW-MC were markedly improved compared to CW-B and CW-M, reaching 82.72%, 95.72% and 93.43%, respectively. Moreover, the global warming potential (CO2 equivalent) of CW-MC was reduced by 52.80% and 36.88% relative to CW-B and CW-M, respectively. Mixing of MO with AC reduced the loss of manganese and further enhanced the manganese cycling process by X-ray photoelectron spectroscope and concentration of Mn(Ⅱ) in CWs analysis. The introduction of MO and AC enhanced the PN/PS ratio of extracellular polymeric substances and facilitated extracellular electron transfer (EET). Furthermore, metagenomic analysis showed that the abundances of denitrifying, manganese oxidizing and electroactive bacteria genera were enhanced in the CW-MC, which promoted the transformation of nitrogen and manganese. Meanwhile, high abundances of denitrification and EET related genes were observed in CW-MC, improving denitrification efficiency and reducing N2O emission. This study elucidated the impacts and mechanisms of MO and AC on GHG emissions, providing a new insight to improve manganese-based CW performance.

Microbial-induced reassembly of phosphate sol: New insight into the removal and fixation of divalent manganese in natural aquatic environment

The commonly used precipitation method struggles to effectively remove low-concentration heavy metals from water. Herein, we demonstrate that the formation of non-settleable phosphate sols at a low low-concentration is the main reason by using phosphate precipitation as an example and report a new method called microbial-induced reassembly (MIR) of the phosphate sols for the removal and fixation of divalent manganese (Mn(II)) from low-concentration wastewater under neutral conditions. Under the induction of microorganisms, the Mn3(PO4)2 sols formed in low Mn(II) concentration could be reassembled into larger and flower-like precipitates with good settleability, allowing for the removal and fixation of low-concentration Mn(II) through natural settlement. Moreover, MIR is able to reduce Mn(II) levels from 10 mg/L to as low as 0.1 mg/L, achieving nearly 100% removal. The interaction between bacterial protein functional groups and Mn2+ ions drives the reassembly of Mn3(PO4)2 sols. MIR of phosphate sol is applicable to both Gram-negative bacteria, such as Escherichia coli, and Gram-positive bacteria, such as Staphylococcus aureus, as well as mixed aerobes. It is also suitable for the removal and fixation of other heavy metals like copper and zinc. This study offers a novel approach for the removal of low-concentration heavy metals from water, more importantly provides a new insight into the migration and fixation of heavy metals in the form of phosphate precipitates induced by microbes in natural aquatic environments.

Mineralizing Biofilm towards Sustainable Conversion of Plastic Wastes to Hydrogen

The integration of inorganic materials with biological machinery to convert plastics into fuels offers a promising strategy to alleviate environmental pollution and energy crisis. Herein, we develop a type of hybrid living material via biomineralization of CdS onto Shewanella oneidensis-based biofilm, which is capable of sustainable hydrogen production from poly(lactic acid) (PLA) wastes under daylight. We reveal that the formed biofilm microstructure provides an independent anaerobic microenvironment that simultaneously supports cellular viability, maintains hydrogenase activity, and preserves the functional stability of CdS, giving rise to the efficient plastic-to-hydrogen conversion efficiency as high as 3751 μmol H2 g-1 PLA. Besides, by genetically engineering transmembrane pili conduit and incorporating conductive nanomaterials to strengthen the electron transfer across cellular interface and biofilm matrices, we show that the conversion efficiency is further enhanced to 5862 μmol H2 g-1 PLA. Significantly, we exhibit that a long-term sustainable plastic-to-hydrogen conversion of 63 d could be achieved by periodically replenishing PLA wastes. Overall, by the synergistic integration of biotic-abiotic characteristics the developed biofilm-based biomineralized hybrid living material is anticipated to provide a new platform toward the efficient conversion of plastic wastes into valuable fuels, and bridge the gap between environmental contamination and green energy production.

Co-occurrence of direct and indirect extracellular electron transfer mechanisms during electroactive respiration in a dissimilatory sulfate reducing bacterium

Understanding the extracellular electron transfer mechanisms of electroactive bacteria could help determine their potential in microbial fuel cells (MFCs) and their microbial syntrophy with redox-active minerals in natural environments. However, the mechanisms of extracellular electron transfer to electrodes by sulfate-reducing bacteria (SRB) remain underexplored. Here, we utilized double-chamber MFCs with carbon cloth electrodes to investigate the extracellular electron transfer mechanisms of Desulfovibrio vulgaris Hildenborough (DvH), a model SRB, under varying lactate and sulfate concentrations using different DvH mutants. Our MFC setup indicated that DvH can harvest electrons from lactate at the anode and transfer them to cathode, where DvH could further utilize these electrons. Patterns in current production compared with variations of electron donor/acceptor ratios in the anode and cathode suggested that attachment of DvH to the electrode and biofilm density were critical for effective electricity generation. Electron microscopy analysis of DvH biofilms indicated DvH utilized filaments that resemble pili to attach to electrodes and facilitate extracellular electron transfer from cell to cell and to the electrode. Proteomics profiling indicated that DvH adapted to electroactive respiration by presenting more pili- and flagellar-related proteins. The mutant with a deletion of the major pilus-producing gene yielded less voltage and far less attachment to both anodic and catholic electrodes, suggesting the importance of pili in extracellular electron transfer. The mutant with a deficiency in biofilm formation, however, did not eliminate current production indicating the existence of indirect extracellular electron transfer. Untargeted metabolomics profiling showed flavin-based metabolites, potential electron shuttles.IMPORTANCEWe explored the application of Desulfovibrio vulgaris Hildenborough in microbial fuel cells (MFCs) and investigated its potential extracellular electron transfer (EET) mechanism. We also conducted untargeted proteomics and metabolomics profiling, offering insights into how DvH adapts metabolically to different electron donors and acceptors. An understanding of the EET mechanism and metabolic flexibility of DvH holds promise for future uses including bioremediation or enhancing efficacy in MFCs for wastewater treatment applications.

Enhanced chloramphenicol biodegradation and sustainable electricity generation via co-cultured electroactive biofilms modified with in-situ self-assembled gold nanoparticles and reduced graphene oxide

Bioelectrochemical technology emerges as a promising approach for addressing the challenge of antibiotic residue contamination. This research innovated by incorporating in-situ self-assembled gold nanoparticles (Au-NPs) and reduced graphene oxide (rGO) into a co-cultured electroactive biofilm (EAB) of Raoultella sp. DB-1 and Shewanella oneidensis MR-1 (Au-rGO@R/S-C). Supported by the rGO scaffold, the embedding of Au-NPs at key intercellular sites, and the adhesion of extracellular polymeric substance (EPS), the Au-rGO@R/S-C EAB enhanced the bioelectrochemical performance of the inoculated microbial fuel cell (MFC), with a 34.4% increase in the maximum voltage output and a 1.95-fold rise in the maximum power density, enabling the complete degradation of 100 mg/L chloramphenicol within 24 h. Notably, the Au-rGO@R/S-C EAB adapted to increased chloramphenicol stress by amplifying EPS secretion, especially with an elevated protein/polysaccharide ratio. Further analysis indicated a positive correlation between excessive production of EPS, particularly the increase in tightly bound EPS, and the stability in balancing the self-protection and extracellular electron transfer efficiency of the Au-rGO@R/S-C EAB under environmental stress. Our findings present a crucial strategy for the rational engineering of EABs, leveraging their dual potential in both environmental remediation and clean energy production.

Long-term performance and mechanism of in-situ biogenetic sulfidated zero-valent iron for enhanced nitrate reduction

The biogenetic sulfidation of zero-valent iron (BS-ZVI) by sulfate-reducing bacteria (SRB) has been demonstrated to enhance the reactivity of ZVI. However, long-term performance of BS-ZVI and related mechanism were still unknown. Therefore, columns containing sponge iron and SRB are built to prepare BS-ZVI in-situ and study its long-term performance. Over 80 % of NO3‾ was reduced to NH4+ by in-situ BS-ZVI within 140 days, which was higher than the sole ZVI treatment (40 %-60 %). The bonding of ZVI and FeSx was in-situ firstly and finally loaded on ZVI. The reduction of Fe(III) by S(-II) and SRB contributed to the formation of FeSx, which improved the electrons transfer. Moreover, BS-ZVI enhanced the enzymes activity of SRB, thus accelerating the metabolic transformation of lactic acid to acetic acid. The accumulation of acetic acid enhanced the removal efficiency of NO3‾ through the dissolution of passivation layer. Overall, this study demonstrated a reactivity enhancement of ZVI through biogenetic sulfidation, which provided a new alternative method for the remediation of groundwater.

Boosting the Microbial Electrosynthesis of Formate by Shewanella oneidensis MR-1 with an Ionic Liquid Cosolvent

Microbial electrosynthesis (MES) is a rapidly growing technology at the forefront of sustainable chemistry, leveraging the ability of microorganisms to catalyze electrochemical reactions to synthesize valuable compounds from renewable energy sources. The reduction of CO2 is a major target application for MES, but research in this area has been stifled, especially with the use of direct electron transfer (DET)-based microbial systems. The major fundamental hurdle that needs to be overcome is the low efficiency of CO2 reduction largely attributed to minimal microbial access to CO2 owing to its low solubility in the electrolyte. With their tunable physical properties, ionic liquids present a potential solution to this challenge and have previously shown promise in facilitating efficient CO2 electroreduction by increasing the CO2 solubility. However, the use of ionic liquids in MES remains unexplored. In this study, we investigated the role of 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) using Shewanella oneidensis MR-1 as a model DET strain. Electrochemical investigations demonstrated the ability of S. oneidensis MR-1 biocathodes to directly convert CO2 to formate with a faradaic efficiency of 34.5 ± 26.1%. The addition of [EMIM][Ac] to the system significantly increased cathodic current density and enhanced the faradaic efficiency to 94.5 ± 4.3% while concurrently amplifying the product yield from 34 ± 23 μM to 366 ± 34 μM. These findings demonstrate that ionic liquids can serve as efficient, biocompatible cosolvents for microbial electrochemical reduction of CO2 to value-added products, holding promise for more robust applications of MES.

Electro-stimulated biodegradation of dimethyl disulfide: Insights from biofilm spatial structure and key functional genes

As a typical sulfur-containing volatile organic compound, dimethyl disulfide (DMDS) is known for its high toxicity and resistance to degradation, necessitating efficient control in environmental media. To address the limitations of biological treatment in degradation capacity, this study employs electro-stimulation to promote DMDS elimination by a porous polyaniline@carbon nanotube bioanode developed on graphite sheet (PANI@CNT/GS). Compared with the unmodified GS bioanode, the PANI@CNT/GS bioanode demonstrates significant advantages in biofilm activity, redox property, and DMDS degradation efficiency. Kinetics analysis shows that the maximum degradation rate of the PANI@CNT/GS bioanode was 0.60 mM h-1, which is 1.36 times higher than that of the control. Characterization results reveal that the highly active biofilms in PANI@CNT/GS bioanode possess 1.40 times the amount of living cells and a 12.5% increase in thickness, contributing to the notable enhancement in DMDS degradation capacity. Additionally, functional gene annotation indicates that the PANI@CNT/GS electrode facilitates the motility and activity of microbial cells and enriches the genes encoding key enzymes involved in DMDS metabolism. This work validates the feasibility of electro-stimulation for enhancing DMDS degradation and further provides in-depth insights into the process intensification mechanism from the perspectives of biofilm spatial structure and key functional genes.

Insight into the responses of the anammox granular sludge system to tetramethylammonium hydroxide (TMAH) during chip wastewater treatment

Tetramethylammonium hydroxide (TMAH), an extensively utilized photoresist developer, is frequently present in ammonium-rich wastewater from semiconductor manufacturing, and its substantial ecotoxicity should not be underestimated. This study systematically investigated the effects of TMAH on the anammox granular sludge (AnGS) system and elucidated its inhibitory mechanisms. The results demonstrated that the median inhibitory concentration of TMAH for anammox was 84.85 mg/L. The nitrogen removal performance of the system was significantly decreased after long-term exposure to TMAH (0-200 mg/L) for 30 days (p < 0.05), but it showed adaptability to certain concentrations (≤50 mg/L). Concurrently, the stability of the granules decreased dramatically, resulting in the breakdown of AnGS. Further investigations indicated that TMAH exposure increased the secretion of extracellular polymeric substances but weakened their defense function. The increase in reactive oxygen species resulted in damage to the cell membrane. Reduced activity of anammox bacteria, impeded electron transfer, and changes in enzyme activity suggested that TMAH affected the metabolic activity. Microbiological analysis revealed that TMAH caused a decrease in the abundance of anammox bacteria and a weakening of symbiotic interactions within the microbial community. These results provide valuable guidance for the AnGS system application in chip wastewater treatment.

Intra/extracellular electron transfer and metagenomic analysis elucidated the roles of magnetic iron powder (Fe3O4) on mixotrophic denitrification system

Elemental iron provides a viable strategy to improve the denitrification efficiency by expediting electron transport. However, the roles of magnetic iron powder (Fe3O4) on mixotrophic denitrification remains unknown. In this study, the intra/extracellular electron transfer (IET/EET) and microbial metabolism mechanisms were explored in a Fe3O4-mediated sulfide-autotrophic and heterotrophic denitrification system. The results showed that Fe3O4 promoted the formation of dense clump structure with filamentous cross-linking in activated sludge. Fe3O4 could increase the coenzyme Q activity in IET and the content of free riboflavin and cytochrome c in EET. Metagenomic analysis indicated that denitrification, sulfide oxidation and sulfate reduction were the main pathways of nitrogen and sulfur metabolism, and the enriched denitrifying bacteria (Halomonas and Hypobacterium) and sulfur-oxidizing bacteria (Marinicella) could stably support nitrate removal. This study expands our understanding of the IET/EET during Fe3O4-mediated mixotrophic denitrification process, providing a novel insight for nitrogen removal from marine recirculating aquaculture wastewater.

Deciphering the biodegradation of thiamethoxam by Phanerochaete chrysosporium with natural siderite: Synergistic mechanisms, transcriptomics characterization, and molecular simulation

Fungi play vital roles in the fate of organic pollutants, particularly when interacting with minerals in aquatic and soil environments. Mechanisms by which fungi may mitigate pollutions in fungus-mineral interactions are still unclear. Inspired by biogeochemical cycling, we constructed a range of co-culture systems to investigate synergistic effects of the white-rot fungus Phanerochaete chrysosporium and the iron-bearing mineral siderite on thiamethoxam (THX) transformation, a common neonicotinoid pesticide. Co-culturing with siderite significantly enhanced THX transformation during the initial 10 days with a dose effect, achieving 86 % removal within 25 days. Fungi could affect siderite's dissolution, transformation, and precipitation through their biological activities. These interactions triggered physiological adaptation and resilience in fungi. Siderite could enhance the activity of fungal ligninolytic enzymes and cytochrome P450, facilitating biotransformation. Genes expression related to growth, energy metabolism, and oxidative stress response upregulated, enhancing fungal resilience to THX. The primary THX degradation pathways included nitro-reduction, C-N cleavage, and de-chlorination. Molecular dynamics simulations provided insights into catalytic mechanisms of enzyme-THX interactions. Together, siderite could act as natural enhancers that endowed fungi to resist physical and chemical stresses in environments, providing insights into contaminants attenuation, fungal biomineralization, and the coevolution of the Earth's lithosphere and biosphere.

3D-printed controllable bio-accelerators with sustained release property to boost chromium (VI) inhibited denitrification recovery

Although soluble bio-accelerators have proven effective in mitigating Cr(VI) inhibition within denitrification system, issues persist in immobilizing bio-accelerators and making them slow-release for sustained regulation. In this study, a novel strategy was proposed to fabricate immobilized bio-accelerators with controlled structure, sustained release property by 3D printing technology. Notably, the sustained release of bio-accelerators from 3D-printed bio-accelerators (3DP-B) lasted for at least 144 h. Compared to control group, 3DP-B with basic components (3DP-BB) shortened the recovery time by 1.4 folds, and the COD and NO3--N removal efficiency was 36.5 % and 38.0 % higher than that of natural recovery. Correspondingly, the activity of key enzymes (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), electron transfer system activity and extracellular polymer substances of denitrification biofilm maintained at relatively high levels. Furthermore, introducing 60 mg·L-1 anthraquinone-2,6-disulfonate (AQDS) into the ink showed noticeable superiority on the bio-inhibition release over 1000 mg·L-1 AQDS. The released AQDS facilitated the electron transport capacity by 1.25 times compared with control group. The groundbreaking findings of this study could advance the development of 3D printing technology and utilization of bio-accelerators in the field of wastewater treatment.

Regulatory roles of extracellular polymeric substances in uranium reduction via extracellular electron transfer by Desulfovibrio vulgaris UR1

The pathway of reducing U(VI) to insoluble U(IV) using electroactive bacteria has become an effective and promising approach to address uranium-contaminated water caused by human activities. However, knowledge regarding the roles of extracellular polymeric substances (EPS) in the uranium reduction process involving in extracellular electron transfer (EET) mechanisms is limited. Here, this study isolated a novel U(VI)-reducing strain, Desulfovibrio vulgaris UR1, with a high uranium removal capacity of 2.75 mM/(g dry cell). Based on a reliable EPS extraction method (45 °C heating), manipulation of EPS in D. vulgaris UR1 suspensions (removal or addition of EPS) highlighted its critical role in facilitating uranium reduction efficiency. On the second day, U(VI) removal rates varied significantly across systems with different EPS contents: 60.8% in the EPS-added system, 48.5% in the pristine system, and 22.2% in the EPS-removed system. Characterization of biogenic solids confirmed the reduction of U(VI) by D. vulgaris UR1, and the main products were uraninite and UO2 (2.88-4.32 nm in diameter). As EPS formed a permeable barrier, these nanoparticles were primarily immobilized within the EPS in EPS-retained/EPS-added cells, and within the periplasm in EPS-removed cells. Multiple electroactive substances, such as tyrosine/tryptophan aromatic compounds, flavins, and quinone-like substances, were identified in EPS, which might be the reason for enhancement of uranium reduction via providing more electron shuttles. Furthermore, proteomics revealed that a large number of proteins in EPS were enriched in the subcategories of catalytic activity and electron transfer activity. Among these, iron-sulfur proteins, such as hydroxylamine reductase (P31101), pyruvate: ferredoxin oxidoreductase (A0A0H3A501), and sulfite reductase (P45574), played the most critical role in regulating EET in D. vulgaris UR1. This work highlighted the importance of EPS in the uranium reduction by D. vulgaris UR1, indicating that EPS functioned as both a reducing agent and a permeation barrier for access to heavy metal uranium.

Reduction of methane and nitrous oxide emissions from stormwater bioretention cells through microbial electrolytic cells

This study investigated the reduction of methane (CH4) and nitrous oxide (N2O) emissions from stormwater bioretention cells through microbial electrolytic cell (MEC), showing the largest reduction of 32.21 % (CH4) at 9.2 μA/m2 of current density and 56.16 % (N2O) at 3.5 μA/m2 of current density, compared with the corresponding in the control (0 μA/m2 of current density). Kinetic of CH4 and N2O emissions could be well fitted by Logistic model with high correlation coefficient (R2 > 0.9500) and model efficiency (ME > 0.95) but low relative root mean square error (RRMSE < 7.88). The increase of pmoA and polysaccharide (PS) were responsible for CH4 reduction, while N2O reduction was attributed to the decrease of nirS and the increase for nosZ and protein (PN), which could explain the lowest GWPd (10.67 mgCO2-eq/m2/h) at 3.5 μA/m2 of current density, suggesting that MEC could be promising for the reduction of CH4 and N2O emissions from bioretention cells.

An in-depth analysis of microbial response to exposure to high concentrations of microplastics in anaerobic wastewater fermentation

The impact of microplastics (MPs) in anaerobic wastewater treatment on microbial metabolism is significant. Anaerobic granular sludge (AS) and biofilm (BF) are two common ways, and their responses to microplastics will have a direct impact on their application potential. This study investigated the microbial reactions of AS and BF to three types of MPs: polyethylene (PE), polyvinyl chloride (PVC), and a mixture of both (MIX). Results exhibited that MPs reduced methane output by 44.65 %, 55.89 %, and 53.18 %, elevated short-chain fatty acid (SCFA) levels by 95.93 %, 124.49 %, and 110.78 %, and lowered chemical oxygen demand (COD) removal by 28.77 %, 36.78 %, and 33.99 % for PE-MP, PVC-MP, and MIX-MP, respectively, with PVC-MP showing the greatest inhibition. Meanwhile, microplastics also facilitated the relative production of reactive oxygen species (ROS, 40.29 %-96.99 %), lactate dehydrogenase (LDH, 20.01 %-75.02 %), and adenosine triphosphate (ATP, 26.64 %-43.80 %), while reducing cytochrome c (cyt c, 23.60 %-49.02 %) and extracellular polymeric substances (EPS, 17.44 %-26.58 %). AS and BF displayed distinct enzymatic activities under MPs exposure. Correspondingly, 16S-rRNA sequencing indicated that AS was mainly involved in acetate generation by Firmicutes, while BF performed polysaccharide degradation by Bacteroidota. Metatranscriptomic analysis showed AS to be rich in acetogens (Bacillus, Syntrophobacter) and methanogens (Methanothrix, Methanobacterium), while BF contained more fermentation bacteria (Mesotoga, Lentimicrobium) and electroactive microorganisms (Clostridium, Desulfuromonas) under MIX-MP. Moreover, BF exhibited higher glycolysis gene expression, whereas AS was more active in methane metabolism, primarily through the acetoclastic methanogenic pathway's direct acetate conversion. This study provides new insights into understanding the microbial response produced by microplastics during anaerobic wastewater digestion.

Potential Application of Room Temperature Synthesized MIL-100(Fe) in Enhancing Methane Production in Microbial Electrolysis Cells-Anaerobic Digestion Treating Protein-Rich Wastewater

Microbial electrolysis cell-anaerobic digestion (MEC-AD) is an emerging technology for methane production. However, low substrate degradation efficiency remains a challenge when processing protein substrates. This study developed a MIL-100(Fe) carbon cloth anode to enhance methane production and substrate degradation in MEC-AD. The effects of MIL-100(Fe) prepared under hydrothermal (H-MIL-100(Fe)) and room temperature conditions (R-MIL-100(Fe)) were compared. Results indicated that H-MIL-100(Fe) and R-MIL-100(Fe) increased cumulative methane production by 16.01% and 14.99%, respectively compared to normal cloth, each influencing methane production through distinct mechanisms. Electrochemical characterization showed that H-MIL-100(Fe) enhanced the electrochemical performance more significantly due to the enrichment of Geotalea, with the oxidation current improved by 7.39-fold (R-MIL-100(Fe) increased it by only 2.95-fold) to promote growth of Methanobacterium. Metagenomic analysis revealed that R-MIL-100(Fe) tended to metabolize amino acids into methane rather than support cellular life activities, indicating its practicality under limited substrate concentration. In summary, R-MIL-100(Fe) shows greater potential for application due to its mild synthesis conditions and advantages in treating complex substrates.

Insights into the role of electrochemical stimulation on sulfur-driven biodegradation of antibiotics in wastewater treatment

The presence of antibiotics in wastewater poses significant threat to our ecosystems and health. Traditional biological wastewater treatment technologies have several limitations in treating antibiotic-contaminated wastewaters, such as low removal efficiency and poor process resilience. Here, a novel electrochemical-coupled sulfur-mediated biological system was developed for treating wastewater co-contaminated with several antibiotics (e.g., ciprofloxacin (CIP), sulfamethoxazole (SMX), chloramphenicol (CAP)). Superior removal of CIP, SMX, and CAP with efficiencies ranging from 40.6 ± 2.6 % to 98.4 ± 1.6 % was achieved at high concentrations of 1000 μg/L in the electrochemical-coupled sulfur-mediated biological system, whereas the efficiencies ranged from 30.4 ± 2.3 % to 98.2 ± 1.4 % in the control system (without electrochemical stimulation). The biodegradation rates of CIP, SMX, and CAP increased by 1.5∼1.9-folds under electrochemical stimulation compared to the control. The insights into the role of electrochemical stimulation for multiple antibiotics biodegradation enhancement was elucidated through a combination of metagenomic and electrochemical analyses. Results showed that sustained electrochemical stimulation significantly enriched the sulfate-reducing and electroactive bacteria (e.g., Desulfobulbus, Longilinea, and Lentimicrobiumin on biocathode and Geobactor on bioanode), and boosted the secretion of electron transport mediators (e.g., cytochrome c and extracellular polymeric substances), which facilitated the microbial extracellular electron transfer processes and subsequent antibiotics removal in the sulfur-mediated biological system. Furthermore, under electrochemical stimulation, functional genes associated with sulfur and carbon metabolism and electron transfer were more abundant, and the microbial metabolic processes were enhanced, contributing to antibiotics biodegradation. Our study for the first time demonstrated that the synergistic effects of electrochemical-coupled sulfur-mediated biological system was capable of overcoming the limitations of conventional biological treatment processes. This study shed light on the mechanism of enhanced antibiotics biodegradation via electrochemical stimulation, which could be employed in sulfur-mediated bioprocess for treating antibiotic-contaminated wastewaters.

The effects of graphene on low-temperature anammox process: The insights from short-term tests and long-term operation

Effluent quality deterioration caused by seasonal low temperature is a great challenge to the application of anammox technology. Here, the effects of different graphene materials on anammox process were investigated under both optimal temperature and low-temperature. The batch tests showed that at 30 °C, 300 mg/L of reduced graphene oxide‑sodium alginate gel (RGOSA) had the most significant promoting effect, reaching nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 95 % and 8.88 mgN/L/d, respectively. The changes of EPS secretion patterns and increasing of key enzymes activity might contribute to the enhanced anammox activity. During the long-term operation of anammox reactor, the NRE and NRR of the reactor decreased when the temperature dropped to 15 °C, showing an NRE of 50 %-57 % with the addition of 200 mg/L of reduced graphene oxide (RGO) and 40 %-45 % with the addition of 20 mg/L of RGO. Furthermore, specific anammox activity (SAA) of the RGO200 reactor at 15 °C increased by 57.1 % compared to the UASB reactor without graphene addition. Additionally, 16S rRNA and metagenomic analysis results revealed anammox bacteria Ca. Kuenenia was the dominant bacteria. Moreover, the RGO can significantly increase the relative abundance of N-converting functional genes. This study demonstrates the graphene materials can help anammox process adapting to low temperatures, providing a possible solution for the application of anammox technology.

Vanadium (V) reduction and the performance of electroactive biofilms in microbial fuel cells with Shewanella putrefaciens

The electron transfer ability of biofilms significantly influences the electrochemical activity of microbial fuel cells (MFCs). However, there is limited understanding of pentavalent vanadium (V(V)) bioreduction and microbial response characteristics in MFCs. In this study, the effect of gradient concentrations of V(V) on the performance of EABs with Shewanella putrefaciens in MFCs was investigated. The results showed that as V(V) concentration increased (0-100 mg/L), the voltage output, power densities, polarization, and electrode potential decreased. V(V) was found to act as an electron acceptor and was reduced during MFCs operation, with a yield of 83.16% being observed at 25 mg/L V(V). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicated declining electrochemical performance of the MFCs with escalating V(V) concentration. The content of protein and polysaccharide from extracellular polymeric substances (EPS) in anodic biofilms increased to 66.75 and 49.15 mg/L at 75 mg/L V(V), respectively. Three-dimensional fluorescence spectroscopy confirmed increased humic substances in EPS extraction with V(V) exposure. The functional genes narG, nirK, and gor involved in V(V) reduction were upregulated with rising V(V) concentration through quantitative polymerase chain reaction (qPCR) analysis. Additionally, riboflavin, cytochrome c, nicotinamide adenine dinucleotide (NADH), and electron transport system activity (ETSA), key indicators for assessing electron transfer behavior, exhibited a negative correlation with various V(V) concentrations, decreasing by 31.81%, 57.14%, 67.39%, and 51.41%, respectively, at a concentration of 100 mg/L V(V) compared to the blank control. These findings contribute valuable insights into the response of EABs to V(V) exposure, presenting potential strategies for enhancing their effectiveness in the treatment of vanadium-contaminated wastewater.