Extracellular Electron Transfer Process Research Articles

Promotion of direct electron transfer between Shewanella putrefaciens CN32 and carbon fiber electrodes via in situ growth of α-Fe2O3 nanoarray

The iron transport system plays a crucial role in the extracellular electron transfer process of Shewanella sp. In this study, we fabricated a vertically oriented α-Fe2O3 nanoarray on carbon cloth to enhance interfacial electron transfer in Shewanella putrefaciens CN32 microbial fuel cells. The incorporation of the α-Fe2O3 nanoarray not only resulted in a slight increase in flavin content but also significantly enhanced biofilm loading, leading to an eight-fold higher maximum power density compared to plain carbon cloth. Through expression level analyses of electron transfer-related genes in the outer membrane and core genes in the iron transport system, we propose that the α-Fe2O3 nanoarray can serve as an electron mediator, facilitating direct electron transfer between the bacteria and electrodes. This finding provides important insights into the potential application of iron-containing oxide electrodes in the design of microbial fuel cells and other bioelectrochemical systems, highlighting the role of α-Fe2O3 in promoting direct electron transfer.

Boosting power output in microbial fuel cell with sulfur-doped MXene/polypyrrole hydrogel anode for enhanced extracellular electron transfer process

Boosting power output in microbial fuel cell with sulfur-doped MXene/polypyrrole hydrogel anode for enhanced extracellular electron transfer process

Significance of a minor pilin PilV in biofilm cohesion of Geobacter sulfurreducens

Bacterial adhesion plays a vital role in forming and shaping the structure of electroactive biofilms that are essential for the performance of bioelectrochemical systems (BESs). Type IV pili are known to mediate cell adhesion in many Gram-negative bacteria, but the mechanism of pili-mediated cell adhesion of Geobacter species on anode surface remains unclear. Herein, a minor pilin PilV2 was found to be essential for cell adhesion ability of Geobacter sulfurreducens since the lack of pilV2 gene depressed the cell adhesion capability by 81.2% in microplate and the anodic biofilm density by 23.1 % at −0.1 V and 37.7 % at −0.3 V in BESs. The less cohesiveness of mutant biofilms increased the charge transfer resistance and biofilm resistance, which correspondingly lowered current generation of the pilV2-deficient strain by up to 63.2 % compared with that of the wild-type strain in BESs. The deletion of pilV2 posed an insignificant effect on the production of extracellular polysaccharides, pili, extracellular cytochromes and electron shuttles that are involved in biofilm formation or extracellular electron transfer (EET) process. This study demonstrated the significance of pilV2 gene in cell adhesion and biofilm formation of G. sulfurreducens, as well as the importance of pili-mediated adhesion for EET of electroactive biofilm.

Hierarchical modulation of extracellular electron transfer processes in microbial fuel cell anodes for enhanced power output through improved Geobacter adhesion

Although microbial fuel cell (MFC) technology is nearing practical realization, the challenge of attaining higher power output continues to impede its widespread implementation. In this study, we successfully developed free-standing three-dimensional high-performance anode materials for MFCs using a straightforward "one-step" process based on garlic. The resulting anode not only promotes the accumulation of biomass and the enrichment of exoelectrogen Geobacter but also facilitates interfacial extracellular electron transfer. This led to rapid start-up within just three days, a robust power density of 12.37 W/m3, and an impressive 24.04 % coulombic efficiency in mixed-culture MFC reactors. Our investigation into the underlying mechanisms of exocellular electron transfer revealed improvements in both direct electron transfer and mediated electron transfer processes. Notably, the fabrication of carbonized garlic MFC anodes proves to be technically competitive and economically relevant. It not only paves the way for the development of high-performance MFCs but also provides valuable insights for the rational design of materials related to microbial electrochemical technologies.

An integrated constructed wetland-Microbial fuel cell system with sewage sludge-biochar to enhance treatment and energy recovery efficiencies

Constructed wetlands and microbial fuel cells (CW-MFCs) are a promising green and sustainable wastewater treatment technology. However, the power production performance of CW-MFCs has long been limited by low-performance cathodes. In this study, we designed two CW-MFC systems using cheap and readily available sewage sludge biochar (SSB) as the substrate for the experimental units. The integration of SSB significantly facilitated the removal of chemical oxygen demand, ammonium nitrogen, total nitrogen, and total phosphorus. Moreover, SSB enhanced the electrochemical performance of the air cathode, resulting in higher power density (44.64 mW/m2) and lower internal resistance (900.00 Ω) compared to gravel-integrated CW-MFC (0.88 mW/m2, 2057.14 Ω). In addition, a typical electroactive bacterium---Geobacter was enriched in the SSB-integrated CW-MFC system. The iron oxides and graphic nitrogen of the SSB favor the growth of Geobacter, and the redox-active groups on the surface of SSB accelerate the extracellular electron transfer process, contributing to the enhancement of treatment performance. Meanwhile, the metal and nitrogen doping improves the oxygen reduction reaction activity and conductivity of SSB, enhancing the cathode area of CW-MFC and improving the energy recovery. Overall, these results demonstrated that SSB-integrated CW-MFC can be a competitive technology for effective wastewater treatment and energy recovery.

Iron-doped cross-linked puffed carbon as capacitive anode for the enhancement of bioelectron storage capacity in microbial fuel cells

Microbial fuel cell (MFC) can utilize the metabolism of electroactive microorganisms to remove organic pollutants from wastewater, and the application of capacitive anodes can enhance the power generation capacity of MFC and the energy storage capacity of bioelectronics. This research aimed to create a capacitive anode with a large specific surface area and excellent electrical conductivity. To achieve this aim, iron-doped cross-linked puffed carbon (CPC–Fe) was prepared for the modification of carbon cloth (CC) substrates by a simple one-step expansion carbonization method using FeCl3·6H2O and maltose as raw materials. The surface structure characterization confirms the successful incorporation of Fe atoms, with Fe3O4 accounting for 79.61%. Fe3O4 exhibits excellent specific capacitance characteristics and can also serve as a good conductor for the transmission or reception of electrons generated by electroactive bacteria. Furthermore, the mesoporous volume of CPC-Fe significantly increases, which contributes to the enhancement of the specific capacitance of material and the improvement of charge storage capacity. Based on these advantages, the maximum power density of MFC equipped with CPC-Fe/CC anode reaches 1850.50 mW m−2. The CPC-Fe/CC bioanode has a cumulative total charge of 1076.02 C m−2, showing good capacitive behaviour and exhibiting a significant enrichment effect on Geobacter species. This study demonstrates that the regulation of extracellular electron transfer (EET) process based on bioelectronic reception steps can not only enhance the power generation performance of MFC, but also effectively improve the energy storage capacity of MFC, which offers significant knowledge for the development of electrode design in other bioelectrochemical systems.

Bioelectricity facilitates carbon dioxide fixation by Alcaligenes faecalis ZS-1 in a biocathodic microbial fuel cell (MFC)

The CO2 fixation mechanism by Alcaligenes faecalis ZS-1 in a biocathode microbial fuel cell (MFC) was investigated. The closed-circuit MFC (CM) exhibited a significantly higher CO2 fixation rate (10.7%) compared to the open-circuit MFC (OC) (2.0%), indicating that bioelectricity enhances CO2 capture efficiency. During the inward extracellular electron transfer (EET) process, riboflavin concentration increased in the supernatant while cytochrome levels decreased. Genome sequencing revealed diverse metabolic pathways for CO2 fixation in strain ZS-1, with potential dominance of rTCA and C4 pathways under electrotrophic conditions as evidenced by significant upregulation of the ppc gene. Differential metabolite analysis using LC-MS demonstrated that CM promoted upregulation of various lipid metabolites. These findings collectively highlight that ZS-1 simultaneously generated electricity and fixed CO2 and that the ppc associated with bioelectricity played a critical role in CO2 capture. In conclusion, bioelectricity resulted in a significant enhancement in the efficiency of CO2 fixation and lipid production.

Retraction for Yadav et al., "The bidirectional extracellular electron transfer process aids iron cycling by Geoalkalibacter halelectricus in a highly saline-alkaline condition".

In our paper, we reported the bidirectional extracellular electron transfer capability of Geoalkalibacter halelectricus based on biochemical (i.e., with insoluble Fe-oxide and Fe(0)) and bioelectrochemical (i.e., with electrodes) experimental approaches. We noticed some issues and limitations of the methods and techniques that were used to analyze Fe species, particularly the reduced Fe ions in insoluble and precipitated Fe(II) minerals that led to incorrect interpretation of the results, specifically the reduction of Fe(III) to Fe(0) in this study. We were made aware of thermodynamic constraints that would make the biological reduction of Fe(III) to Fe(0) implausible. Hence, the conclusion about microbial Fe(III)-oxide reduction to Fe(0) is invalid. We also noticed errors in estimating the protein-based iron reduction/oxidation rates and faradic efficiencies, besides the limitations of the methods used for Fe analysis. For these reasons, we retract this article and sincerely apologize for the inconvenience it may have caused to the readers.

Response of biocurrent conduction to soil microenvironment

The biocurrent generated by soil extracellular electron transfer (EET) partly drives biogeochemical cycles and controls soil quality. However, it is unclear how the soil abiotic and biotic conditions affect the biocurrent conduction. In this study, the response relationship of soil microenvironment and in-situ biocurrent was studied. The results showed that red soil exhibited the optimal electron transfer efficiency, as evidenced by the maximum current density and accumulated charge output, with increments of 56–93 % and 80–2800 %, respectively, compared with the other five types of soils. Soil physicochemical properties were the most important factor on the biocurrent generation, and further the quantity and bioavailability of dissolved organic matter, NH4+-N content, and lower pH were predictive indicators for the exoelectrogenic processes of soils. In addition, the high soil biocurrent was likely determined by a complex synergistic network of the transformation of carbon and nitrogen, electroactive bacteria involving the functions of cell wall/membrane and cytochrome enzyme metabolism and transport related EET process. Overall, we provide an insight into the relationship among soil biocurrent conduction, physicochemical properties, bacteria community and metabolic function, and a support for bioelectrochemical technology application.

Synthesis of palladium nanoparticles utilizing biotemplates and investigation of their synergistic catalytic performance

AbstractBACKGROUNDPalladium nanoparticles can act as a shuttle to accelerate the extracellular electron transfer (EET) by exoelectrogens. Through the EET process, microorganisms drive the redox cycle of many substances. The palladium nanoparticle has a variety of catalytic activities and activities can be significantly improved by combining with the active effects of microorganisms.RESULTSIn this study, Staphylococcus saprophyticus JJ‐1 was utilized as a biological template carrier to synthesize palladium nanoparticles that were immobilized on the bacterial surface. The morphology and composition of palladium were characterized by various techniques including transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Furthermore, the hydrogenation activity of the synthesized Pd was tested at room temperature and atmospheric pressure using methyl orange as a model pollutant. Electrochemical characterization was carried out by cyclic voltammetry and potentiostatic measurements. The research demonstrated that palladium nanoparticles acted as both electronic mediators and catalysts in the dye reduction process, while S. saprophyticus JJ‐1 contributed to stabilizing nanoparticles and electrochemical activity. The synergistic effect between these two components significantly enhances MO degradation efficiency.CONCLUSIONThis study presented an energy‐saving method to synthesize an integrated catalyst based on the synergistic interaction between biomass and nanoparticles, offering a novel approach for developing environmentally friendly, cost‐effective, and efficient integrated catalysts. © 2024 Society of Chemical Industry (SCI).

Interdisciplinary Research on Electrons and Biofilms

Interdisciplinary research on electrons and biofilms is being carried out by Assistant Professor Dr Yoshihide Tokunou, Faculty of Life and Environmental Sciences, University of Tsukuba, Japan. His work is aimed at gaining a deeper understanding of the role of electrons in bacterial society and exploring the process of bacterial extracellular electron transfer (EET) in biofilms. By combining microbiology and electrochemistry, Dr Tokunou is developing EET-based biotechnologies and improving our understanding of the physiological importance of EET in bacterial society. To achieve this, he is collaborating with various experts such as microbiologists, chemists, and engineers, including Professor Dr Nobuhiko Nomura. His current interest is in the EET process that terminates with soluble electron acceptors. By regulating the EET in biofilms respiring with oxygen, he is trying to control various biofilm-related phenomena such as host-bacteria interaction, antibiotic resistance of biofilms, biochemical production from biofilms, etc.

Microbial corrosion of CoCrMnNi high entropy alloy by Pseudomonas aeruginosa through electron transfer between Mn and microbe

The microbiologically influenced corrosion of CoCrMnNi high entropy alloy induced by P. aeruginosa was investigated in this work. The results of electrochemical tests, time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy showed that the thickness of passive film was significantly decreased in the presence of P. aeruginosa and the corrosion of HEA was accelerated. When the organic nutrients were deficient, the extracellular electron transfer process was promoted and the corrosion resistance of the HEA was further decreased according to the results of potentiodynamic polarization and Mott-Schottky. The effect of nutrients deficiency on MIC acceleration was more prominent after the degradation of the passive film. Mn metal in the HEA substrate preferentially participated in the bacterial metabolism as an alternative energy source due to the high activity.

Electrostatic self-assembled nickel cobalt sulfide/Ti3C2 Mxene as a bio-capacitive anode for specific attracting sulfur-cycling bacteria and regulating extracellular electron transfer efficiency

Microbial fuel cells have been proposed as one of the sustainable and potential technologies for treating contaminants and synchronously producing green energy. However, the poor performance of the anode is a major obstacle in the practical application of MFCs. To address this challenge, the rational design of anode materials with enhanced biocatalytic and biocompatible properties has been considered as an effective approach to improve extracellular electron transfer (EET) processes and general MFC performance. Herein, in light of the interaction between the transition metal and exoelectrogens, nickel-cobalt sulfide/Ti3C2 Mxene (NiCo2S4/Mxene) is prepared by electrostatic assembly, which combined positively charged sea-urchin-like NiCo2S4 with negatively charged Mxene. This not only prevents the stacking of NiCo2S4 and Mxene but also accelerates the EET process by harnessing their biocompatibility and biocatalyst. As expected, the MFC with NiCo2S4/Mxene harvested higher electricity energy (9.66 ± 0.28 W/m3), significantly exceeded those of plain carbon felt (CF, 1.68 ± 0.13 W/m3), Mxene (4.32 ± 0.20 W/m3) and NiCo2S4 (5.41 ± 0.22 W/m3). Moreover, the microbial community analysis further revealed that the sulfide composite attracts a higher percentage of sulfur-cycling exoelectrogens (Desulfuromonas (24.25%) and Marinobacterium (15.75%)), motivating associated metabolic pathways with more efficient electricity generation processes. Such commendable performances are mainly attributed to the synergistic effect between NiCo2S4 and Mxene, which confers the bioanode with good biocompatibility and biocatalyst for biofilm adhesion and colonization, as well as providing abundant transition metals and sulfide active sites for the EET process. Our finding provides a facile routine for developing sulfide with appropriate modification as anode material for favorable performance of MFC, providing insights for sustainable and cleaner energy production in the future.

Biosynthesis of biogenic ferrous sulfide as a potential electron shuttle for enhanced Cr(VI) removal by Shewanella oneidensis MR-1

Biological reduction of Cr(VI) is considered to be one of the most efficient approaches for bioremediation of Cr(VI) contaminated sites, but the slow electron transfer rate between microorganisms and Cr(VI) is a bottleneck for its practical application. The addition of ecofriendly electron shuttle can provide an effective solution to this bottleneck. In this study, a novel electron shuttle of biogenic ferrous sulfide (Bio-FeS) was biosynthesized by Shewanella oneidensis MR-1(MR-1) and employed to improve the extracellular electron transfer (EET) rate from MR-1 strain to Cr(VI) and accelerate reduction of Cr(VI). Results showed that the Cr(VI) removal rates by MR-1 was remarkably increased by 12.4 times with the addition of Bio-FeS as electron shuttle. The Cr(VI) reduction was highly pH dependent. Electrochemical analysis confirmed that the presence of Bio-FeS can accelerate EET process. The mechanism analysis indicated that Bio-FeS enhance Cr(VI) reduction by MR-1 through promoting the secretion of more extracellular polymeric substances (EPS) and enhancing EET rate. Most of Cr(VI) was converted to Cr(III) by MR-1, and then is removed from the solution in the form of precipitations, and EPS play a crucial role in Cr(VI) reduction, adsorption and complexation. This study demonstrates the significant influence of Bio-FeS on Cr(VI) reduction and provides a promising technology for the development of cost-effective Cr(VI) remediation technologies.

Magnetite-equipped algal-rich sediments for microbial fuel cells: Remediation of sediment organic matter pollution and mechanisms of remote electron transfer

Using the bio-electrochemical methods for the restoration of high algae sediments is full of potential and challenges. How to promote extracellular electron transfer (EET) process in microbial fuel cells (MFC) is the key bottleneck. The study had explored the potential application of magnetite on accelerating electron transfer for improving the output of MFC and sediment pollution remediation. The results indicated that the organic matter degradation rate showed a remarkable increase of 27.45 %, and the voltage output was approximately 1.68 times higher compared to the MFC configured with regular sediment. Abundant electroactive bacteria (EABs), such as Geobacter and Burkholderiaceae, and fermentative bacteria were responsible for these results, accompanied by the enhanced fluorescence of humic substances (HS), increased concentration and activity of cytochrome C (25.05 % and 21.12 %), as well as elevated extracellular polymeric substance content. Moreover, the intrinsic EET mechanisms among Fe-oxides, HS, and EABs were explored. According to the electrochemical analysis and substance transformation, the EET process involved four stages: magnetite-enhanced direct electron transfer via strong conductivity, iron respiration mediating electron transfer to the electrode, the model quinone substance acting as an electron shuttle facilitating EET and iron reduction, and iron cycling mediating electron transfer. This study provides an effective strategy for pollution remediation in algal-rich sediment, which was beneficial for the harmless treatment and resource utilization of both algae and sediment, simultaneously.

N-Doped Carbon Nanowire-Modified Macroporous Carbon Foam Microbial Fuel Cell Anode: Enrichment of Exoelectrogens and Enhancement of Extracellular Electron Transfer.

Microbial fuel cell (MFC) performance is affected by the metabolic activity of bacteria and the extracellular electron transfer (EET) process. The deficiency of nanostructures on macroporous anode obstructs the enrichment of exoelectrogens and the EET. Herein, a N-doped carbon nanowire-modified macroporous carbon foam was prepared and served as an anode in MFCs. The anode has a hierarchical porous structure, which can solve the problem of biofilm blockage, ensure mass transport, favor exoelectrogen enrichment, and enhance the metabolic activity of bacteria. The microscopic morphology, spectroscopy, and electrochemical characterization of the anode confirm that carbon nanowires can penetrate biofilm, decrease charge resistance, and enhance long-distance electron transfer efficiency. In addition, pyrrolic N can effectively reduce the binding energy and electron transfer distance of bacterial outer membrane hemin. With this hierarchical anode, a maximum power density of 5.32 W/m3 was obtained, about 2.5-fold that of bare carbon cloth. The one-dimensional nanomaterial-modified macroporous anodes in this study are a promising strategy to improve the exoelectrogen enrichment and EET for MFCs.

Unique corrosion reinforcement mechanism of pipeline oil sludge with sulfate-reducing bacteria on X60 steel and the targeted long-term inhibition of dazomet delivery

The mutual promotion behavior of pipeline oil sludge and wild SRB on pipeline steel corrosion was investigated. The resistance probe technique was used for long-term monitoring of MIC underneath SRB oil sludge. Corrosion of pipeline steel under oil sludge was the result of multifactorial coupling. SRB biofilm enhanced the conductivity of the oil sludge that serves as an electron transfer "bridge" between the SRB and carbon steel, accelerating the extracellular electron transfer process of MIC, and hence the dissolution of the carbon steel. Delivery of dazomet (DMTT) was a long-term strategy for mitigating pipeline corrosion under SRB oil sludge.

Enhancing extracellular electron transfer and power generation in microbial fuel cell using a ferrocene-based conjugated oligoelectrolyte

The anode compartment, as an electron generation station, determines the power performance and contaminant removal in microbial fuel cell (MFC). However, the extracellular electron transfer (EET) process limits bioelectricity generation. In this work, the role of conjugated oligoelectrolytes (COEs) on catalyzing bacterial activity toward bio-current production was investigated. In this regard, two COEs, namely [4-[1-(3-methylimidazolium chloride)]butyl] ferrocene (MIF+) and Bis [4-[1-(3-methylimidazolium chloride)]butyl] ferrocene (BMIF+) were synthesized and the increases in anodic current output were probed through MFC device. The electrochemical analyses revealed excellent performance in bio-current production for BMIF+ stained cells. The tolerance threshold of COEs stained cells for different concentrations of COEs was investigated using chronoamperometry (CA) test. Additionally, the power performance of MFC exhibited the highest value of 115.46 mW m−2 for the BMIF+ stained cells in comparison with MIF+ stained cells (73.12 mW m−2) and unstained cells (25.8 mW m−2). The results demonstrated that spiking cells' membranes with COEs is a meaningful strategy to facilitate the EET process and produce bioelectricity.

In-situ constructed metallic Mo decorated MoS2 nanosheets on carbon cloth as excellent anode for efficient current generation and Cr(Ⅵ) removal

The anode, as the host site of exoelectrogens, is considered to be a crucial factor in determining the current generation of microbial fuel cells (MFCs), which is constrained by sluggish extracellular electron transfer (EET) on the exoelectrogens/anode interface. To facilitate the EET efficacy, herein, MoS2 nanosheets decorated with metallic Mo are rational designed to grow vertically and uniformly on carbon cloth (CC). This not only avoids the use of bonding agents, but also compensates for the inherent defects of MoS2 semiconductors, displaying an extremely low charge-transfer impedance of 4.6 Ω and a remarkable specific area capacitance of 435.97 F/m2. As expected, MFC equipped with Mo/MoS2-CC anode was faster started up for 1.35 d, achieving a superior power density of 3.25 W/m2 (8.15 d, 1.96 W/m2, CC), which is attributed to the continuous modification of CC surface properties via Mo/MoS2 nanosheets, boosting the electroactive bacterial attachment and EET process. Most importantly, the enhanced current intensity of Mo/MoS2-CC anode provides more robust and sustained electron for the cathodic Cr(Ⅵ) reduction, acquiring about 100% removal of Cr(Ⅵ) at the initial Cr(Ⅵ) concentration of 40 mg/L (75.5%, CC). This work exhibits a new idea for high performance anode design and long-term efficient Cr(Ⅵ) removal.

Characterization of the inner membrane cytochrome ImcH from Geobacter reveals its importance for extracellular electron transfer and energy conservation.

Electroactive bacteria combine the oxidation of carbon substrates with an extracellular electron transfer (EET) process that discharges electrons to an electron acceptor outside the cell. This process involves electron transfer through consecutive redox proteins that efficiently connect the inner membrane to the cell exterior. In this study, we isolated and characterized the quinone-interacting membrane cytochrome c ImcH from Geobacter sulfurreducens, which is involved in the EET process to high redox potential acceptors. Spectroscopic and electrochemical studies show that ImcH hemes have low midpoint redox potentials, ranging from - 150 to -358 mV, and connect the oxidation of the quinol-pool to EET, transferring electrons to the highly abundant periplasmic cytochrome PpcA with higher affinity than to its homologues. Despite the larger number of hemes and transmembrane helices, the ImcH structural model has similarities with the NapC/NirT/NrfH superfamily, namely the presence of a quinone-binding site on the P-side of the membrane. In addition, the first heme, likely involved on the quinol oxidation, has apparently an unusual His/Gln coordination. Our work suggests that ImcH is electroneutral and transfers electrons and protons to the same side of the membrane, contributing to the maintenance of a proton motive force and playing a central role in recycling the menaquinone pool. This article is protected by copyright. All rights reserved.