Extracellular Electron Transfer Research Articles

External electricity-powered FeS/graphene/bacterial hybrid for Cr6+ removal from water lacking organic electron donors

Microbial reduction is an economical and environmentally benign route to deal with high-toxic Cr6+ widely present in aquatic environments, but faces major challenges such as cytotoxicity and insufficient organic electron donors. Herein, we propose a route for the removal of Cr6+ from water using a ternary FeS/reduced graphene oxide/Shewanella oneidensis MR-1 (FeS/rGO/MR-1) hybrid with external electricity supply at an electrode potential of −0.36 V. The biohybrid with excellent redox activity is in-situ biosynthesized by virtue of the versatile metabolic pathway and powerful extracellular electron transfer ability of MR-1 cells without the need of organic carbon sources. The biohybrid is directly used to remove Cr6+ under the condition of continuous electricity input, the removal rate is negatively correlated with the applied electrode potential. Compared with binary FeS/MR-1 and rGO/MR-1 counterpart, the FeS/rGO/MR-1 hybrid achieves an improved ability to remove Cr6+ at an initial concentration of 20 mg L−1 in three consecutive batches due to the synergistic effect. The FeS is the main active component for rapid chemical reduction of Cr6+ because of its highly reducible Fe2+ and S2-, and rGO acts as the bridge to accelerate electron transfer from the applied electrode to MR-1 cells. Then, the MR-1 cells use the obtained electrons for FeS regeneration, which in turn reduces Cr6+ again, resulting in the precipitation of less toxic Cr3+ [Cr(OH)3 and Cr2O3] in the biohybrid. This study provides a feasible route for removal of toxic Cr6+ from water lacking organic electron donor by in-situ synthesis of biohybrid with external electricity supply.

Carbon nanotubes mediate electron transfer between Shewanella oneidenis MR-1 and nano zero-valent iron to enhance the elimination of Cr(VI) from aqueous media

Nano zero-valent iron (nZVI) has been widely employed for the elimination of heavy metals from wastewater. However, the practical application of nZVI is greatly limited due to its fast aggregation and surface passivation. In this study, a carbon nanotube-supported nZVI composite (nZVI@CNTs) was synthesized and coupled with Shewanella oneidensis MR-1 to enhance the removal of Cr(VI) from aqueous media. The results demonstrated that the coupling of nZVI@CNTs and MR-1 (nZVI@CNTs/MR-1) exhibited superior performance in eliminating Cr(VI) compared to using nZVI@CNTs or MR-1 alone. Electrochemical characterization demonstrated that CNTs acting as electron shuttles improve the electron transfer from MR-1 to nZVI, thus facilitating the passivation layer dissolution. XRD analysis proved that MR-1 can effectively promote the dissolution of the Fe(III) passivation layer with the existence of CNTs. FTIR and XPS analyses confirmed that CNTs contain many functional groups (such as C − C and C = O) related to extracellular electron transfer, thus promoting the electron transfer of MR-1 to nZVI. Three-dimensional excitation-emission matrix (3D-EEM) analysis showed that the extracellular polymeric substances (EPS) generated from MR-1 participated in the Cr(VI) elimination. The mechanism analysis demonstrated the Fe(II) dissolved from the nZVI passivation layer reduces Cr(VI) to Cr(III) and then removes it by co-precipitation, and the EPS secreted by MR-1 also participates in the Cr(VI) adsorption and reduction. Generally, the coupling of nZVI@CNTs and MR-1 successfully addresses the drawbacks of nZVI and demonstrates a remarkable ability to remove Cr(VI).

Electrode potential regulates extracellular polymer secretion enhanced tetracycline removal

Bacteria colonized on solid electrode developing electroactive biofilm (EAB) has been shown to promote the contaminants biodegradation. Regulating electrode potential can improve the stability of extracellular electron transfer (EET), but how the electrode potential regulating the extracellular polymer secretion and the tetracycline (TC) removal has not been fully studied. Here, EAB cultured at 0 V was used to study the degradation mechanism of TC at different electrode potentials. Results showed that −0.1 V was the optimized electrode potential for TC biodegradation compared with 0.1 V, 0 V and −0.3 V, which was 28 % higher than that without electric field. Stimulation of electric field can retain proper extracellular polymer (EPS) to relieve the poison of TC, while excessive extracellular polysaccharide (PS) at 0 V have hindered the contact between microorganisms and TC, thus limited electron transfer and reduced the TC biodegradation efficiency. Excessively negative potential (−0.3 V) will restrict the electron transfer which was not conducive to the biodegradation of organic pollutants. Microbial community analysis revealed that TC addition have refreshed the EAB structure, Dokdonella and Norank_f_Rikenellaceae replaced Geobacter as the dominant species in EAB to promote TC biodegradation. The variation of metabolic pathway was suggested that the up-regulation of pyruvate metabolism and ubiquinone synthesis at −0.1 V have promoted the TC removal. This study has provided theoretical support for the electrode potential regulating the extracellular polymer secretion and promoting the pollution bioremediation.

Facilely Prepared Carbon Dots as Effective Anode Modifier for Enhanced Performance of Microbial Fuel Cells.

Microbial fuel cells (MFCs) are a promising technology for obtaining energy in wastewater. Effective extracellular electron transfer is one of the key factors for its practical application. In this work, carbon dots (CDs) enriched with oxygen-containing groups on the surface were synthesized as an efficient anode modifier using a simple hydrothermal method and common reactants. The experimental findings indicated that anodes modified with CDs exhibited increased electrical conductivity and greater hydrophilicity. These modifications facilitated increased microorganism loading and contributed to enhancing electrochemical processes within the anode biofilm. The CD-modified MFCs exhibited higher maximum power density (661.1 ± 42.6 mW·m-2) and open-circuit voltage (534.50 ± 6.4 mV), which were significantly better than those of the blank group MFCs (484.1 ± 14.1 mW·m-2 and 447.50 ± 12.1 mV). The use of simple carbon materials to improve the microbial loading on the MFCs anode and the electron transfer between the microbial-electrode may provide a new idea for the design of efficient MFCs.

A hybrid transistor with transcriptionally controlled computation and plasticity

Organic electrochemical transistors (OECTs) are ideal devices for translating biological signals into electrical readouts and have applications in bioelectronics, biosensing, and neuromorphic computing. Despite their potential, developing programmable and modular methods for living systems to interface with OECTs has proven challenging. Here we describe hybrid OECTs containing the model electroactive bacterium Shewanella oneidensis that enable the transduction of biological computations to electrical responses. Specifically, we fabricated planar p-type OECTs and demonstrated that channel de-doping is driven by extracellular electron transfer (EET) from S. oneidensis. Leveraging this mechanistic understanding and our ability to control EET flux via transcriptional regulation, we used plasmid-based Boolean logic gates to translate biological computation into current changes within the OECT. Finally, we demonstrated EET-driven changes to OECT synaptic plasticity. This work enables fundamental EET studies and OECT-based biosensing and biocomputing systems with genetically controllable and modular design elements.

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.

Effect of lignocellulosic biomass components on the extracellular electron transfer of biochar-based microbe-electrode in microbial electrochemical systems

Biomass-derived carbon-based electrodes with good biocompatibility, sustainability, and low cost are competitive in microbial electrochemical systems. Unfortunately, biomass composition is complex, and biochar performance is dependent on the kind of biomass, making quantitative function control difficult. Three-dimensional (3D) lignocellulosic carbon-based electrodes were generated in this study by varying the ratios of three natural biopolymers (cellulose, lignin, and hemicellulose). The biopolymer contents significantly impacted the material's physicochemical and electrochemical properties. Only the proper ratio of these natural polymers can ensure the 3D structure's integrity and mechanical strength after carbonization. The greater the cellulose content and the lower the hemicellulose (xylan) content, the lower the ohmic and charge transfer resistance. The maximum power density (Pmax) of the microbial fuel cells equipped with the biopolymer-based anode ranged between 4.5 and 4.8 W m−2, setting a new record for biocarbon electrodes. The highest Pmax was observed when the cellulose, lignin, and xylan ratios were 1:3:2 (4.80 ± 0.04 W m−2). The Pmax correlates with cellulose content more than lignin and xylan and with material capacitance more than with other parameters. High cellulose content facilitates electron transfer but reduces the capacitance of carbon-based electrodes. The material's electron transfer resistance and capacitance contribute to the opposite of the Pmax. So, the interaction with multiple properties influences the electrode performance. This research revealed the effects of natural biopolymer compositions on electrode performance, which was helpful for quantitatively modifying functional carbon-based materials.

Mechanisms of extracellular electron transfer in anaerobic methanotrophic archaea

Anaerobic methanotrophic (ANME) archaea are environmentally important, uncultivated microorganisms that oxidize the potent greenhouse gas methane. During methane oxidation, ANME archaea engage in extracellular electron transfer (EET) with other microbes, metal oxides, and electrodes through unclear mechanisms. Here, we cultivate ANME-2d archaea (‘Ca. Methanoperedens’) in bioelectrochemical systems and observe strong methane-dependent current (91–93% of total current) associated with high enrichment of ‘Ca. Methanoperedens’ on the anode (up to 82% of the community), as determined by metagenomics and transmission electron microscopy. Electrochemical and metatranscriptomic analyses suggest that the EET mechanism is similar at various electrode potentials, with the possible involvement of an uncharacterized short-range electron transport protein complex and OmcZ nanowires.

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).

Harnessing the potential of ginkgo biloba extract: Boosting denitrification performance through accelerated electron transfer

Ginkgo biloba extract (GBE) had several effects on the human body as one of the widely used phytopharmaceuticals, but it had no application in microbial enhancement in the environmental field. The study focused on the impact of GBE on denitrification specifically under neutral conditions. At the identified optimal addition ratio of 2% (v/v), the system exhibited a noteworthy increase in nitrate reduction rate (NRR) by 56.34%, elevating from 0.71 to 1.11 mg-N/(L·h). Moreover, the extraction of microbial extracellular polymeric substance (EPS) at this ratio revealed changes in the composition of EPS, the electron exchange capacity (EEC) was enhanced from 87.16 to 140.4 μmol/(g C), and the transfer impedance was reduced within the EPS. The flavin, fulvic acid (FA), and humic acid (HA) provided a π-electron conjugated structure for the denitrification system, enhancing extracellular electron transfer (EET) by stimulating carbon source metabolism. GBE also improved electron transfer system activity (ETSA) from 0.025 to 0.071 μL O2/(g·min·prot) and the content of NADH enhanced by 22.90% while significantly reducing the activation energy (Ea) by 85.6% in the denitrification process. The synergy of improving both intracellular and extracellular electron transfer, along with the reduction of Ea, notably amplified the initiation and reduction rates of the denitrification process. Additionally, GBE demonstrated suitability for denitrification across various pH levels, enhancing microbial resilience in alkaline conditions and promoting survival and proliferation. Overall, these findings open the door to potential applications of GBE as a natural additive in the environmental field to improve the efficiency of denitrification processes, which are essential for nitrogen removal in various environmental contexts.

Synergistic Control of Trimethoprim and the Antimicrobial Resistome in Electrogenic Microbial Communities.

Synergistic control of the risks posed by emerging antimicrobials and antibiotic resistance genes (ARGs) is crucial for ensuring ecological safety. Although electrogenic respiration can enhance the biodegradation of several antimicrobials and reduce ARGs accumulation, the association mechanisms of antimicrobial biodegradation (trimethoprim, TMP) with the fate of the antimicrobial resistome remain unclear. Here, the biotransformation pathway of TMP, microbial associations, and functional gene profiles (e.g., degradation, antimicrobial resistance, and electron transfer) were analyzed. The results showed that the microbial electrogenic respiration significantly enhanced the biodegradation of TMP, especially with a cosubstrate sodium acetate supply. Electroactive bacteria enriched in the electrode biofilm positively correlated with potential TMP degraders dominated in the planktonic communities. These cross-niche microbial associations may contribute to the accelerated catabolism of TMP and extracellular electron transfer. Importantly, the evolution and dissemination of overall ARGs and mobile genetic elements (MGEs) were significantly weakened due to the enhanced cometabolic biodegradation of TMP. This study provides a promising strategy for the synergistic control of the water ecological risks of antimicrobials and their resistome, while also highlighting new insights into the association of antimicrobial biodegradation with the evolution of the resistome in an electrically integrated biological process.

Rice root Fe plaque increases paddy soil CH4 emissions via the promotion of electron transfer for syntrophic methanogenesis

Iron (Fe) plaque is a concentrated form of microbially available Fe oxide that coats rice plant root surfaces, representing a high density of Fe oxide and which potentially mediates paddy soil CH4 emissions. Using a combination of methods including Fe plaque induction, isotopic labeling, pure microbial strains, and Fe oxide addition experiments, we investigated the impact of Fe plaque on methane (CH4) emissions from paddy soils and explored the associated mechanisms underlying the influence of Fe plaque on CH4 emissions. A 13C–CH4 isotopic labeling experiment showed that Fe plaque did not significantly affect CH4 oxidation and associated gene expression, whereas Fe plaque significantly enriched methanogenic archaea and their expression of genes associated with methanogenesis. Pure microbial strain and Fe oxide addition experiments showed that the enhancement of CH4 production in the presence of Fe plaque was caused by the (semi) conductive minerals within the Fe plaque, specifically, hematite, which promoted the extracellular electron transfer between the methanogenic archaea and their syntrophic bacteria, resulting in enhancement of methanogenesis. Our results imply that the presence of Fe plaque will accelerate CH4 emissions from paddy soils and suppressing Fe plaque has the potential to mitigate CH4 emissions.

Effects of extracellular electron transfer on biomineralization by Shewanella putrefaciens in damaged organic coatings

This study reports the effect of extracellular electron transfer (EET) on biomineralization mediated by Shewanella putrefaciens in damaged coatings under different carbon source conditions. S. putrefaciens was able to obtain energy from metal surfaces to support metabolism via EET when the carbon source was insufficient. Under these conditions, bacteria colonized the coating scratches, resulting in accelerated corrosion instead of mineralization. The EIS results revealed that biomineralization was most significant in the 75% carbon source medium after 7 days of incubation. Interestingly, the pH of the medium increased with an abundance of carbon sources, which promoted biomineralization.

Electrochemical Characterization of Two Gut Microbial Strains Cooperatively Promoting Multiple Sclerosis Pathogenesis.

In this study, we explored the extracellular electron transfer (EET) capabilities of two bacterial strains, OTU0001 and OTU0002, which are demonstrated in biofilm formation in mouse gut and the induction of autoimmune diseases like multiple sclerosis. OTU0002 displayed significant electrogenic behaviour, producing microbial current on an indium tin-doped oxide electrode surface, particularly in the presence of glucose, with a current density of 60 nA/cm2. The presence of cell-surface redox substrate potentially mediating EET was revealed by the redox-based staining method and electrochemical voltammetry assay. However, medium swapping analyses and the addition of flavins, a model redox mediator, suggest that the current production is dominated by soluble endogenous redox substrates in OTU0002. Given redox substrates were detected at the cell surface, the secreted redox molecule may interact with the cellular surface of OTU0002. In contrast to OTU0002, OTU0001 did not exhibit notable electrochemical activity, lacking cell-surface redox molecules. Further, the mixture of the two strains did not increase the current production from OTU0001, suggesting that OTU0001 does not support the EET mechanism of OTU0002. The present work revealed the coexistence of EET and non-EET capable pathogens in multi-species biofilm.

Soil Humic Acid Stimulates Potentially Active Dissimilatory Arsenate-Reducing Bacteria in Flooded Paddy Soil as Revealed by Metagenomic Stable Isotope Probing.

Dissimilatory arsenate reduction contributes a large proportion of arsenic flux from flooded paddy soil, which is closely linked to soil organic carbon input and efflux. Humic acid (HA) represents a natural ingredient in soil and is shown to enhance microbial arsenate respiration to promote arsenic mobility. However, the community and function profiles of metabolically active arsenate-respiring bacteria and their interactions with HA in paddy soil remain unclear. To probe this linkage, we performed a genome-centric comparison of potentially active arsenate-respiring bacteria in anaerobic microcosms amended with 13C-lactate and HA by combining stable-isotope probing with genome-resolved metagenomics. Indeed, HA greatly accelerated the microbial reduction of arsenate to arsenite. Enrichment of bacteria that harbor arsenate-respiring reductase genes (arrA) in HA-enriched 13C-DNA was confirmed by metagenomic binning, which are affiliated with Firmicutes (mainly Desulfitobacterium, Bacillus, Brevibacillus, and Clostridia) and Acidobacteria. Characterization of reference extracellular electron transfer (EET)-related genes in these arrA-harboring bacteria supports the presence of EET-like genes, with partial electron-transport chain genes identified. This suggests that Gram-positive Firmicutes- and Acidobacteria-related members may harbor unspecified EET-associated genes involved in metal reduction. Our findings highlight the link between soil HA and potentially active arsenate-respiring bacteria, which can be considered when using HA for arsenic removal.

A genetic engineering strategy to enhance outer membrane vesicle-mediated extracellular electron transfer of Geobacter sulfurreducens

Bioelectrochemical systems (BESs) are unique devices that harness the metabolic activity of electroactive microorganisms (EAMs) to convert chemical energy stored in organic substrates into electrical energy. Enhancing electron transfer efficiency between EAMs and electrodes is the key to practical implementation of BESs. Considering the role of outer membrane vesicles (OMVs) in mediating electron transfer of EAMs, a genetic engineering strategy to achieve OMVs overproduction was explored to enhance electron transfer efficiency and the underlying mechanisms were investigated. This study constructed a mutant strain of Geobacter sulfurreducens that lacked the ompA gene encoding an outer membrane protein. Experimental results showed that the mutant strain produced more OMVs and possessed higher electron transfer efficiency in Fe(III) reduction, dye degradation and current generation in BESs than the wild-type strain. More cargoes such as c-type cytochromes, functional proteins, eDNA, polysaccharides and signaling molecules that might be favorable for electron transfer and biofilm formation were found in OMVs produced by ompA-deficient anodic biofilm, which possibly contributed to the improved electron transfer efficiency of ompA-deficient biofilm. The results indicate that overproduction of OMVs in EAMs might be a potential strategy to enhance BESs performance.

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.

Intensified nitrogen and phosphorus removal and mechanism revelation in constructed wetlands amended with iron-carbon based substrate towards low C/N ratio wastewater

Constructed wetlands (CWs) show a promising capability of nutrient removal from the low C/N ratio characterized wastewater with the help of functional substrates, yet the mechanism remains unclear. In this study, sponge iron mixed with biochar was adopted as substrates to construct bench-scale CWs (CW-FeC) treating simulated urban tail water (C/N = 2). Over the experiment, it achieved a prominent performance with total nitrogen (TN) and total phosphorus (TP) removal efficiency of 89.8 and 92.1 %, respectively. Meanwhile, greenhouse gas emissions such as CO2 and N2O were extensively depressed. Mechanism analysis revealed that the deposition of ferrous ions on biochar would enlarge the micro-electrolysis interfaces and amplify the binding sites between P and Fe compared to CW systems with other substrates (gravel, biochar, and gravel mixed with sponge iron remarked as CW-G, CW-C, and CW-FeG). A significant difference regarding the mechanism of N removal was proposed based on the bacterial community analysis. The released ferrous (due to electrolysis and high abundance of iron-reduced bacteria) as electron donors could be easily captured by iron-based autotrophic denitrification bacteria as evidenced by 1.98 times higher the relative abundance of denitrifying bacteria and upregulated related genes expression. In contrast, the iron-oxidized bacteria have to be acclimatized in the CW-FeG to supply electrons for denitrification via interspecies extracellular electron transfer. The positive correlation between iron-redox bacteria and denitrification bacteria further demonstrated the integrity of the iron cycle in CWs for better nitrogen removal. These findings provide an elaborated insight into the nutrient transformation and removal processes interacting with substrates in CWs.

Engineered nanomaterials display a variable interaction with anoxygenic photoelectrogenic biofilm for pharmaceutical pollutants degradation

Engineered nanomaterials (ENMs) have been reported to facilitate extracellular electron transfer (EET) by increasing the electrical conductivity of electroactive biofilms. However, the mechanisms between different ENMs and anoxygenic photoelectrogenic bacteria for degrading organic pollutants remain unclear. In this study, we investigated the mechanism of metronidazole (MNZ) degradation by different concentrations of carbon nanotubes (CNTs), Iron (III) oxide (Fe3O4) NPs, and titanium dioxide (TiO2) NPs in Rhodopseudomonas palustris based photoelectrogenic biofilms. At low concentrations, CNTs enhanced the electrochemical activity and EET capacity of the biofilm, possibly by increasing the DNA concentration and cellular activity in the cathodic biofilm. However, the ecological toxicity of CNTs at high concentrations damaged the activity of R. palustris, resulting in a decline in the MNZ degradation rate (0.29179 h−1 at 185 μg/L and 0.27801 h−1 at 370 μg/L). A high TiO2 NPs concentration (370 μg/L) significantly boosted the MNZ degradation rate (133 % increase) via photocatalytic activity. But it affected the biofilm activity and EET. Overall, Fe3O4 NPs demonstrated superior performance. At 185 μg/L, the photosynthetic current and MNZ degradation rate increased by 138 % and 142 %, respectively. Despite a slowdown in the utilization rate of Fe (III) and EET at high concentrations, the biofilm exhibited sustained high activity, indicating that Fe3O4 NPs can significantly enhance the metabolism of R. palustris. These findings were not only important for optimizing the performance of anoxygenic photoelectrogenic biofilms but also for regulating the ecological impact of ENMs in natural environments.

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.