Electron transport phenomena of electroactive bacteria in microbial fuel cells: a review of Proteus hauseri

Towards a new understanding of bioelectrochemical systems from the perspective of microecosystems: A critical review

Bioelectrochemical system (BES) holds promise for sustainable energy generation and wastewater treatment. The microbial communities, as the core of BES, play a crucial role in its performance, thus needing to be systematically studied. However, researches considering microbial communities in BES from an ecological perspective are limited. This review provided a comprehensive summary of the BES with special emphasis on microecological principles, commencing with the dynamic formation and succession of the microbial communities. It also clarified the intricate interspecies relationships and quorum-sensing mechanisms regulated by dominant species. Furthermore, this review addressed the crucial themes in BES-related researches on ecological processes, including growth patterns, ecological structures, and defense strategies against external disturbances. By offering this novel perspective, it would contribute to enhancing the understanding of BES-centered technologies and facilitating future research in this field.

Enhancement of Electricity Production in Microbial Fuel Cells Using a Biosurfactant-Producing Co-Culture

Microbial fuel cells are bio-electrochemical devices that enable the conversion of chemical energy into bioelectricity. In this manuscript, the use of biosurfactants (Tween 80 and surfactin) and the effect of coculturing E. coli and L. plantarum were used to investigate the generation of bioelectricity coming from an H-type microbial fuel cell. In this setup, E. coli acts as an electron donor while L. plantarum acts as an in situ biosurfactant producer. It was observed that the use of exogenous surfactants enhanced electricity production compared to conventional E. coli cultures. The utilization of Tween 80 and surfactin increased the power generation from 204 µW m-2 to 506 µW m-2 and 577 µW m-2, respectively. Furthermore, co-culturing E. coli and L. plantarum also resulted in a higher power output compared to pure cultures (132.8% more when compared to using E. coli alone and 68.1% more when compared to using L. plantarum alone). Due to the presence of surfactants, the internal resistance of the cell was reduced. The experimental evidence collected here clearly indicates that the production of endogenous surfactants, as well as the addition of exogenous surfactants, will enhance MFC electricity production.

Enhancement of electrode properties using carbon dots functionalized magnetite nanoparticles for azo dye decolorization in microbial fuel cell

Technology integration of nanomaterials with microbial fuel cell (MFC) have led to simultaneous degradation of recalcitrant dyes and energy extraction from textile wastewater. Limited electron transfer capacity and hydrophobicity of electrode are the bottlenecks for enhancing the performance of MFC. Nanomaterials can provide surface functionalities for electron transfers and serve as catalyst for pollutant degradation. In this paper, magnetite nanoparticles functionalized with carbon dots (Fe₃O₄@CDs) were used to enhance the electron transfer capacity of the electrodes due to numerous surface-active functional groups of CDs and the reversible redox reaction of Fe²⁺/Fe³⁺. Polydopamine (PDA) was used as binder to coat Fe₃O₄@CDs onto the surface of carbon felt (CF) electrodes in a sono-chemical reaction, favoring to form biocompatible electrodes. Charge transfer resistance of Fe₃O₄@CDs@PDA-CF was 5.02Ω as compared to 293.34Ω of unmodified CF. Fe₃O₄@CDs@PDA-CF installed MFC could achieve almost 98% dye degradation efficiency within 48 h and 18.30 mW m^-2 power output as compared to 77% dye degradation and 0.34 mW m^-2 power output by unmodified CF electrode MFC. Moreover, metagenomic analysis of microbial consortia developed in Fe₃O₄@CDs@PDA-CF MFC showed enrichment of electrogenic and dye degrading microbial communities of Achromobacter. Delftia, Geobacter and Pseudomonas.

Enhancing the Biological Oxidation of H2S in a Sewer Pipe with Highly Conductive Concrete and Electricity-Producing Bacteria

Hydrogen sulfide (H2S) generated in sewer systems is problematic to public health and the environment, owing to its corrosive consequences, odor concerns, and poison control issues. In a previous work, conductive concrete, based on amorphous carbon with a mechanism that operates as a microbial fuel cell was investigated. The objective of the present study is to develop additional materials for highly conductive concrete, to mitigate the concentration of H2S in sewer pipes. Adsorption experiments were conducted to elucidate the role of the H2S reduction. Additionally, electricity-producing bacteria (EPB), isolated from a municipal wastewater treatment plant, were inoculated to improve the H2S reduction. The experimental results showed that inoculation with EPB could decrease the concentration of H2S, indicating that H2S was biologically oxidized by EPB. Several types of new materials containing acetylene black, or magnetite were discovered for use as conductive concrete, and their abilities to enhance the biological oxidation of H2S were evaluated. These conductive concretes were more effective than the commercial conductive concrete, based on amorphous carbon, in decreasing the H2S concentration in sewer pipes.

Advancements in Bioelectricity Generation Through Nanomaterial-Modified Anode Electrodes in Microbial Fuel Cells

The use of nanotechnology in bioelectrochemical systems to recover bioelectricity and metals from waste appears to be a potentially appealing alternative to existing established procedures. This trend exactly characterizes the current renewable energy production technology. Hence, this review focuses on the improvement of the anode electrode by using different functional metal oxide-conducting polymer nanocomposites to enhance microbial fuel cell (MFC) performance. Enhancement of interfacial bioelectrocatalysis between electroactive microorganisms and hierarchical porous nanocomposite materials could enhance cost-effective bioanode materials with superior bioelectrocatalytic activity for MFCs. In this review, improvement in efficiency of MFCs by using iron oxide- and manganese oxide-based polypyrrole hybrid composites as model anode modifiers was discussed. The review also extended to discussing and covering the principles, components, power density, current density, and removal efficiencies of biofuel cell systems. In addition, this research review demonstrates the application of MFCs for renewable energy generation, wastewater treatment, and metal recovery. This is due to having their own unique working principle under mild conditions and using renewable biodegradable organic matter as a direct fuel source.

Microbial Electrochemical Systems: Principles, Construction and Biosensing Applications

Microbial electrochemical systems are a fast emerging technology that use microorganisms to harvest the chemical energy from bioorganic materials to produce electrical power. Due to their flexibility and the wide variety of materials that can be used as a source, these devices show promise for applications in many fields including energy, environment and sensing. Microbial electrochemical systems rely on the integration of microbial cells, bioelectrochemistry, material science and electrochemical technologies to achieve effective conversion of the chemical energy stored in organic materials into electrical power. Therefore, the interaction between microorganisms and electrodes and their operation at physiological important potentials are critical for their development. This article provides an overview of the principles and applications of microbial electrochemical systems, their development status and potential for implementation in the biosensing field. It also provides a discussion of the recent developments in the selection of electrode materials to improve electron transfer using nanomaterials along with challenges for achieving practical implementation, and examples of applications in the biosensing field.

Bioelectrochemically enhanced degradation of bisphenol S: mechanistic insights from stable isotope-assisted investigations

Electroactive microbes is the driving force for the bioelectrochemical degradation of organic pollutants, but the underlying microbial interactions between electrogenesis and pollutant degradation have not been clearly identified. Here, we combined stable isotope-assisted metabolomics (SIAM) and 13C-DNA stable isotope probing (DNA-SIP) to investigate bisphenol S (BPS) enhanced degradation by electroactive mixed-culture biofilms (EABs). Using SIAM, six 13C fully labeled transformation products were detected originating via hydrolysis, oxidation, alkylation, or aromatic ring-cleavage reactions from 13C-BPS, suggesting hydrolysis and oxidation as the initial and key degradation pathways for the electrochemical degradation process. The DNA-SIP results further displayed high 13C-DNA accumulation in the genera Bacteroides and Cetobacterium from the EABs and indicated their ability in the assimilation of BPS or its metabolites. Collectively, network analysis showed that the collaboration between electroactive microbes and BPS assimilators played pivotal roles the improvement in bioelectrochemically enhanced BPS degradation.

Polyphenolic compounds as electron shuttles for sustainable energy utilization

For renewable and sustainable bioenergy utilization with cost-effectiveness, electron-shuttles (ESs) (or redox mediators (RMs)) act as electrochemical "catalysts" to enhance rates of redox reactions, catalytically accelerating electron transport efficiency for abiotic and biotic electrochemical reactions. ESs are popularly used in cellular respiratory systems, metabolisms in organisms, and widely applied to support global lives. Apparently, they are applicable to increase power-generating capabilities for energy utilization and/or fuel storage (i.e., dye-sensitized solar cell, batteries, and microbial fuel cells (MFCs)). This first-attempt review specifically deciphers the chemical structure association with characteristics of ESs, and discloses redox-mediating potentials of polyphenolics-abundant ESs via MFC modules. Moreover, to effectively convert electron-shuttling capabilities from non-sustainable antioxidant activities, environmental conditions to induce electrochemical mediation apparently play critical roles of great significance for bioenergy stimulation. For example, pH levels would significantly affect electrochemical potentials to be exhibited (e.g., alkaline pHs are electrochemically favorable for expression of such electron-shuttling characteristics). Regarding chemical structure effect, chemicals with ortho- and para-dihydroxyl substituents-bearing aromatics own convertible characteristics of non-renewable antioxidants and electrochemically catalytic ESs; however, ES capabilities of meta-dihydroxyl substituents can be evidently repressed due to lack of resonance effect in the structure for intermediate radical(s) during redox reaction. Moreover, this review provides conclusive remarks to elucidate the promising feasibility to identify whether such characteristics are non-renewable antioxidants or reversible ESs from natural polyphenols via cyclic voltammetry and MFC evaluation. Evidently, considering sustainable development, such electrochemically convertible polyphenolic species in plant extracts can be reversibly expressed for bioenergy-stimulating capabilities in MFCs under electrochemically favorable conditions.

Electricity production enhancement in a constructed wetland-microbial fuel cell system for treating saline wastewater

The use of constructed wetlands in combination with microbial fuel cells (CW-MFC) to treat saline wastewater may enhance electricity production by increasing the ionic strength, reducing internal resistance and stimulating microbes to accelerate electron transfer. In this study, salinity did not significantly inhibit the removal of TP and COD, but TN and NH₄⁺-N removal efficiencies during saline wastewater treatment (ST) were significantly lower than during non-saline wastewater treatment (NT). However, salinity significantly increased the power density (16.4 mW m^-2 in ST and 3.9 mW m^-2 in NT, a 4-fold enhancement) by increasing the electron transfer rate and reducing internal resistance (140.29 Ω in ST and 415.21 Ω in NT). The peptides in extracellular polymeric substances (EPS) acted as electron shuttles to promote the migration of electrons and protons in ST. From start-up to stable operation, though the microorganisms in ST were reduced in diversity relative to NT, the proportion of electrochemically active bacteria (EAB), such as Ochrobactrum, significantly increased (p < 0.05) and gradually predominated in the microbial community.

Comparative static and shaking culture of metabolite derived from methyl red degradation by Lysinibacillus fusiformis strain W1B6

This paper reports on the comparative characteristics and properties of the metabolites derived from methyl red (MR) decolorization by Lysinibacillus fusiformis strain W1B6 under static and shaking conditions. A batch culture system was used to investigate the effect of aeration on azoreductase activity in the biodegradation process, transformation of colour removal and the metabolite products. Biodegradation analysis was monitored using Fourier transform infrared spectroscopy and high-performance liquid chromatography while metabolites were determined using gas chromatography-mass spectroscopy. Phytotoxicity and anti-microbial tests were also conducted to detect the toxicity of metabolites. The results showed that this strain grew more rapidly under shaking conditions while azoreductase activity increased more rapidly under static conditions. Despite that, no significant difference in the decolorization was observed under both static and shaking conditions with up to 96% and 93.6% decolorization achieved, respectively, within 4 h of incubation. MR was degraded into two fragmented compounds, i.e. 2-aminobenzoic acid and N,N-dimethyl-1.4-benzenediamine. The concentration of 2-amino benzoic acid was higher under static conditions resulting the biotransformation of 2-amino benzoic acid into methyl anthranilate more rapidly under static conditions. Other metabolites were also detected as intermediate biotransformation products and by-products. Less or no toxic effect was found in the metabolite degradation products under both culture conditions.

Biochemical characteristics of a nitroreductase with diverse substrate specificity from Streptomyces mirabilis DUT001

A nitroreductase-encoded gene from an efficient nitro-reducing bacterium Streptomyces mirabilis DUT001, named snr, was cloned and heterogeneously expressed in Escherichia coli. The purified Streptomyces nitroreductase SNR was a homodimer with an apparent subunit molecular weight of 24 kDa and preferred NADH to NADPH as a cofactor. By enzyme incubation and isothermal calorimetry experiments, flavin mononucleotide (FMN) was found to be the preferred flavin cofactor; the binding process was exothermic and primarily enthalpy driven. The enzyme can reduce multiple nitro compounds and flavins, including antibacterial drug nitrofurazone, priority pollutants 2,4-dinitrotoluene and 2,4,6-trinitrotoluene, as well as key chemical intermediates 3-nitrophthalimide, 4-nitrophthalimide, and 4-nitro-1,8-naphthalic anhydride. Among the substrates tested, the highest activity of k_cat(app) /K_m(app) (0.234 μM^-1  Sec^-1 ) was observed for the reduction of FMN. Multiple sequence alignment revealed that the high FMN reduction activity of SNR may be due to the absence of a helix, constituting the entrance to the substrate pocket in other nitroreductases.