Isolation and Characterization of a Novel Electrogenic Bacterium, Dietzia sp. RNV-4

Single-Cell Phenotyping of Extracellular Electron Transfer via Microdroplet Encapsulation

Electroactive organisms contribute to metal cycling, pollutant removal, and other redox-driven environmental processes. Studying this phenomenon in high-throughput is challenging since extracellular reduction cannot easily be traced back to its cell of origin within a mixed population. Here, we describe the development of a microdroplet emulsion system to enrich EET-capable organisms. We validated our system using the model electroactive organism S. oneidensis and describe the tooling of a benchtop microfluidic system for oxygen-limited processes. We demonstrated enrichment of EET-capable phenotypes from a mixed wild-type and EET-knockout population. As a proof-of-concept application, bacteria were collected from iron sedimentation from Town Lake (Austin, TX) and subjected to microdroplet enrichment. We observed an increase in EET-capable organisms in the sorted population that was distinct when compared to a population enriched in a bulk culture more closely akin to traditional techniques for discovering EET-capable bacteria. Finally, two bacterial species, C. sakazakii and V. fessus not previously shown to be electroactive, were further cultured and characterized for their ability to reduce channel conductance in an organic electrochemical transistor (OECT) and to reduce soluble Fe(III). We characterized two bacterial species not previously shown to exhibit electrogenic behavior. Our results demonstrate the utility of a microdroplet emulsions for identifying putative EET-capable bacteria and how this technology can be leveraged in tandem with existing methods.

Utilizing a Fe3O4 Magnetite Nanoparticle for Anode Modification in a Microbial Desalination Cell to Treat Saltwater

The microbial desalination cell (MDC) is a bio-electrochemical system that exhibits the ability to oxidize organic compounds, produce energy, and decrease the saline concentrations within the desalination chamber. The selective removal of ions from the desalination chamber is significantly influenced by the anion and cation exchange membranes. In this study, a three-chamber microbial desalination cell was developed to treat seawater using a synthesize Fe3O4 magnetite nanoparticle (MNP)-modified anode. The impact of different performance parameters, such as temperature, pH, and concentrations of NPs, has been investigated in order to assess the performance of three-chamber MDCs in terms of energy recovery and salt removal. The evaluation criteria of the system included multiple factors such as chemical oxygen demand (COD), Coulombic efficiency (CE), desalination efficiency, as well as system aspects including voltage generation and power density. The highest COD% removal efficiency was 74% at 37 °C, pH = 7, and 30 g/L salt concentration with an optimized NPs concentration of 2.0 mg/cm2 impregnated on anode. The maximum Coulombic efficiency was 10.3% with the maximum power density of 4.3 W/m3. The effect of the nanoparticle concentration impregnated on the anode was clarified by the primary factor of analysis. This research has revealed consistent patterns in the enhancement of voltage generation, COD, and Coulombic efficiencies when incorporating higher concentrations of nanoparticles on the anode at a certain point.

Electrogenic Staphylococcus epidermidis colonizes nasal cavities and alleviates IL-6 progression induced by the SARS2-CoV nucleocapsid protein

AIM

Certain probiotic bacteria have been shown to possess an immunomodulatory effect and a protective effect on influenza infections. Using the Staphylococcus epidermidis K1 colonized mice model, we assessed the effect of nasal administration of glycerol or flavin mononucleotide (FMN) on the production of interleukin (IL)-6 mediated by the severe acute respiratory syndrome coronavirus 2 (SARS2-CoV) nucleocapsid protein (NPP).

METHODS AND RESULTS

FMN, one of the key electron donors for the generation of electricity facilitated by S. epidermidis ATCC 12228, was detected in the glycerol fermentation medium. Compared to the S. epidermidis ATCC 12228, the S. epidermidis K1 isolate showed significant expression of the electron transfer genes, including pyruvate dehydrogenase (pdh), riboflavin kinase (rk), 1,4-dihydroxy-2-naphthoate octaprenyltransferase (menA), and type II NADH quinone oxidoreductase (ndh2). Institute of cancer research (ICR) mice were intranasally administered with S. epidermidis K1 with or without pretreatment with riboflavin kinase inhibitors, then nasally treated with glycerol or FMN before inoculating the NPP. Furthermore, J774A.1 macrophages were exposed to NPP serum and then treated with NPP of SARS2-CoV. The IL-6 levels in the bronchoalveolar lavage fluid (BALF) of mice and macrophages were quantified using a mouse IL-6 enzyme-linked immunosorbent assay kit.

CONCLUSIONS

Here, we report that nasal administration of NPP strongly elevates IL-6 levels in both BALF and J774A.1 macrophages. It is worth noting that NPP-neutralizing antibodies can decrease IL-6 levels in macrophages. The nasal administration of glycerol or FMN to S. epidermidis K1-colonized mice results in a reduction of NPP-induced IL-6 production.

Electroactive Bacteria in Natural Ecosystems and Their Applications in Microbial Fuel Cells for Bioremediation: A Review

Electroactive bacteria (EAB) are natural microorganisms (mainly Bacteria and Archaea) living in various habitats (e.g., water, soil, sediment), including extreme ones, which can interact electrically each other and/or with their extracellular environments. There has been an increased interest in recent years in EAB because they can generate an electrical current in microbial fuel cells (MFCs). MFCs rely on microorganisms able to oxidize organic matter and transfer electrons to an anode. The latter electrons flow, through an external circuit, to a cathode where they react with protons and oxygen. Any source of biodegradable organic matter can be used by EAB for power generation. The plasticity of electroactive bacteria in exploiting different carbon sources makes MFCs a green technology for renewable bioelectricity generation from wastewater rich in organic carbon. This paper reports the most recent applications of this promising technology for water, wastewater, soil, and sediment recovery. The performance of MFCs in terms of electrical measurements (e.g., electric power), the extracellular electron transfer mechanisms by EAB, and MFC studies aimed at heavy metal and organic contaminant bioremediationF are all described and discussed.

Isolation and Characterisation of Electrogenic Bacteria from Mud Samples

To develop efficient microbial fuel cell systems for green energy production using different waste products, establishing characterised bacterial consortia is necessary. In this study, bacteria with electrogenic potentials were isolated from mud samples and examined to determine biofilm-formation capacities and macromolecule degradation. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identifications have revealed that isolates represented 18 known and 4 unknown genuses. They all had the capacities to reduce the Reactive Black 5 stain in the agar medium, and 48 of them were positive in the wolfram nanorod reduction assay. The isolates formed biofilm to different extents on the surfaces of both adhesive and non-adhesive 96-well polystyrene plates and glass. Scanning electron microscopy images revealed the different adhesion potentials of isolates to the surface of carbon tissue fibres. Eight of them (15%) were able to form massive amounts of biofilm in three days at 23 °C. A total of 70% of the isolates produced proteases, while lipase and amylase production was lower, at 38% and 27% respectively. All of the macromolecule-degrading enzymes were produced by 11 isolates, and two isolates of them had the capacity to form a strong biofilm on the carbon tissue one of the most used anodic materials in MFC systems. This study discusses the potential of the isolates for future MFC development applications.

Geoalkalibacter halelectricus SAP-1 sp. nov. possessing extracellular electron transfer and mineral-reducing capabilities from a haloalkaline environment

The extracellular electron transfer (EET)-capable electroactive microorganisms (EAMs) play crucial roles in mineral cycling and interspecies electron transfer in different environments and are used as biocatalysts in microbial electrochemical technologies. Studying EAMs from extreme environments is desired to advance the electromicrobiology discipline, understanding their unique metabolic traits with implications to extreme microbiology, and develop specific bioelectrochemical applications. Here, we present a novel haloalkaliphilic bacterium named Geoalkalibacter halelectricus SAP-1, isolated from a microbial electroactive biofilm enriched from the haloalkaline lake sediments. It is a rod-shaped Gram-negative heterotrophic anaerobe that uses various carbon and energy sources and respires on soluble and insoluble terminal electron acceptors. Besides 16S-rRNA and whole-genome-based phylogeny, the GGDC values of 21.7 %, ANI of 78.5, and 2.77 % genomic DNA GC content difference with the closest validly named species Geoalkalibacter ferrihydriticus (DSM 17813^T ) confirmed its novelty. When grown with the solid-state electrode as the only electron acceptor, it produced 460±23 μA/cm² bioelectrocatalytic current, thereby confirming its electroactivity. Further electrochemical analysis revealed the presence of membrane redox components with high formal potentials, putatively involved in the direct mode of EET. These are distinct from EET components reported for any known electroactive microorganisms, including well-studied Geobacter spp., Shewanella spp. and Desulfuromonas acetexigens. Further the capabilities of G. halelectricus SAP-1 to respire soluble as well insoluble electron acceptors including fumarate, SO₄ ^2- , Fe³⁺ , and Mn⁴⁺ suggests its role in cycling these elements in haloalkaline environments. This article is protected by copyright. All rights reserved.

Use of Banana Waste as a Source for Bioelectricity Generation

The large amounts of organic waste thrown into the garbage without any productivity, and the increase in the demand for electrical energy worldwide, has led to the search for new eco-friendly ways of generating electricity. Because of this, microbial fuel cells have begun to be used as a technology to generate bioelectricity. The main objective of this research was to generate bioelectricity through banana waste using a low-cost laboratory-scale method, achieving the generation of maximum currents and voltages of 3.71667 ± 0.05304 mA and 1.01 ± 0.017 V, with an optimal pH of 4.023 ± 0.064 and a maximum electrical conductivity of the substrate of 182.333 ± 3.51 µS/cm. The FTIR spectra of the initial and final substrate show a decrease in the peaks belonging to phenolic compounds, alkanes, and alkenes, mainly. The maximum power density was 5736.112 ± 12.62 mW/cm2 at a current density of 6.501 A/cm2 with a peak voltage of 1006.95 mV. The molecular analysis of the biofilm formed on the anode electrode identified the species Pseudomonas aeruginosa (100%), and Paenalcaligenes suwonensis (99.09%), Klebsiella oxytoca (99.39%) and Raoultella terrigena (99.8%), as the main electricity generators for this type of substrate. This research gives a second use to the fruit with benefits for farmers and companies dedicated to exporting and importing because they can reduce their expenses by using their own waste.

Colonization of nasal cavities by Staphylococcus epidermidis mitigates SARS‐CoV‐2 nucleocapsid phosphoprotein‐induced interleukin (IL)‐6 in the lung

Infection by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) can trigger excessive interleukin (IL)‐6 signalling, leading to a myriad of biological effects including a cytokine storm that contributes to multiple organ failure in severe coronavirus disease 2019 (COVID‐19). Using a mouse model, we demonstrated that nasal inoculation of nucleocapsid phosphoprotein (NPP) of SARS‐CoV‐2 increased IL‐6 content in bronchoalveolar lavage fluid (BALF). Nasal administration of liquid coco‐caprylate/caprate (LCC) onto Staphylococcus epidermidis (S. epidermidis)‐colonized mice significantly attenuated NPP‐induced IL‐6. Furthermore, S. epidermidis‐mediated LCC fermentation to generate electricity and butyric acid that promoted bacterial colonization and activated free fatty acid receptor 2 (Ffar2) respectively. Inhibition of Ffar2 impeded the effect of S. epidermidis plus LCC on the reduction of NPP‐induced IL‐6. Collectively, these results suggest that nasal S. epidermidis is part of the first line of defence in ameliorating a cytokine storm induced by airway infection of SARS‐CoV‐2.

Engineering S. oneidensis for Performance Improvement of Microbial Fuel Cell-a Mini Review

Microbial fuel cell (MFC) is a promising technology that utilizes exoelectrogens cultivated in the form of biofilm to generate power from various types of sources supplied. A metal-reducing pathway is utilized by these organisms to transfer electrons obtained from the metabolism of substrate from anaerobic respiration extracellularly. A widely established model organism that is capable of extracellular electron transfer (EET) is Shewanella oneidensis. This review highlights the strategies used in the transformation of S. oneidensis and the recent development of MFC in terms of intervention through genetic modifications. S. oneidensis was genetically engineered for several aims including the study on the underlying mechanisms of EET, and the enhancement of power generation and wastewater treating potential when used in an MFC. Through engineering S. oneidensis, genes responsible for EET are identified and strategies on enhancing the EET efficiency are studied. Overexpressing genes related to EET to enhance biofilm formation, mediator biosynthesis, and respiration appears as one of the common approaches.

Diverse Microorganisms in Sediment and Groundwater Are Implicated in Extracellular Redox Processes Based on Genomic Analysis of Bioanode Communities

Extracellular electron transfer (EET) between microbes and iron minerals, and syntrophically between species, is a widespread process affecting biogeochemical cycles and microbial ecology. The distribution of this capacity among microbial taxa, and the thermodynamic controls on EET in complex microbial communities, are not fully known. Microbial electrochemical cells (MXCs), in which electrodes serve as the electron acceptor or donor, provide a powerful approach to enrich for organisms capable of EET and to study their metabolism. We used MXCs coupled with genome-resolved metagenomics to investigate the capacity for EET in microorganisms present in a well-studied aquifer near Rifle, CO. Electroactive biofilms were established and maintained for almost 4 years on anodes poised mostly at −0.2 to −0.25 V vs. SHE, a range that mimics the redox potential of iron-oxide minerals, using acetate as the sole carbon source. Here we report the metagenomic characterization of anode-biofilm and planktonic microbial communities from samples collected at timepoints across the study period. From two biofilm and 26 planktonic samples we reconstructed draft-quality and near-complete genomes for 84 bacteria and 2 archaea that represent the majority of organisms present. A novel Geobacter sp. with at least 72 putative multiheme c-type cytochromes (MHCs) was the dominant electrode-attached organism. However, a diverse range of other electrode-associated organisms also harbored putative MHCs with at least 10 heme-binding motifs, as well as porin-cytochrome complexes and e-pili, including Actinobacteria, Ignavibacteria, Chloroflexi, Acidobacteria, Firmicutes, Beta- and Gammaproteobacteria. Our results identify a small subset of the thousands of organisms previously detected in the Rifle aquifer that may have the potential to mediate mineral redox transformations.

Cultivating electroactive microbes-from field to bench

Electromicrobiology is an emerging field investigating and exploiting the interaction of microorganisms with insoluble electron donors or acceptors. Some of the most recently categorized electroactive microorganisms became of interest to sustainable bioengineering practices. However, laboratories worldwide typically maintain electroactive microorganisms on soluble substrates, which often leads to a decrease or loss of the ability to effectively exchange electrons with solid electrode surfaces. In order to develop future sustainable technologies, we cannot rely solely on existing lab-isolates. Therefore, we must develop isolation strategies for environmental strains with electroactive properties superior to strains in culture collections. In this article, we provide an overview of the studies that isolated or enriched electroactive microorganisms from the environment using an anode as the sole electron acceptor (electricity-generating microorganisms) or a cathode as the sole electron donor (electricity-consuming microorganisms). Next, we recommend a selective strategy for the isolation of electroactive microorganisms. Furthermore, we provide a practical guide for setting up electrochemical reactors and highlight crucial electrochemical techniques to determine electroactivity and the mode of electron transfer in novel organisms.

Hydrogen and electrical energy co-generation by a cooperative fermentation system comprising Clostridium and microbial fuel cell inoculated with port drainage sediment

This research work has succeeded in recovering energy from glucose by generating H₂ with the aid of a Clostridium beijerinckii strain and obtaining electrical energy from compounds present in the H₂ fermentation effluent in a microbial fuel cell (MFC) seeded with native port drainage sediment. In the fermentation step, 49.5% of the initial glucose concentration (56 mmol/L) was used to produce 104 mmol/L H₂; 5, 33, 3, and 1 mmol/L acetate, butyrate, lactate, and ethanol also emerged, respectively. MFC tests by feeding the anodic compartment with acetate, butyrate, lactate (individually or as a mixture), or the H₂ fermentation effluent provided power density values ranging between 0.6 and 1.2 W/m². Acetate furnished the highest power density with a nanowire-rich biofilm despite the lowest anode bacterial concentration (10¹² 16S gene copies/g of sediment). Non-conventional exoelectrogenic microbial communities were observed in the acetate-fed MFC; e.g., Pseudomonadaceae (Pseudomonas) and Clostridia (Acidaminobacter, Fusibacter).

Natural Extracellular Electron Transfer Between Semiconducting Minerals and Electroactive Bacterial Communities Occurred on the Rock Varnish

Rock varnish is a thin coating enriched with manganese (Mn) and iron (Fe) oxides. The mineral composition and formation of rock varnish elicit considerable attention from geologists and microbiologists. However, limited research has been devoted to the semiconducting properties of these Fe/Mn oxides in varnish and relatively little attention is paid to the mineral-microbe interaction under sunlight. In this study, the mineral composition and the bacterial communities on varnish from the Gobi Desert in Xinjiang, China were analyzed. Results of principal components analysis and t-test indicated that more electroactive genera such as Acinetobacter, Staphylococcus, Dietzia, and Pseudomonas gathered on varnish bacterial communities than on substrate rock and surrounding soils. We then explored the culture of varnish, substrate and soil samples in media and the extracellular electron transfer (EET) between bacterial communities and mineral electrodes under light/dark conditions for the first time. Orthogonal electrochemical experiments demonstrated that the most remarkable photocurrent density of 6.1 ± 0.4 μA/cm2 was observed between varnish electrode and varnish microflora. Finally, based on Raman and 16S rRNA gene-sequencing results, coculture system of birnessite and Pseudomonas (the major Mn oxide and a common electroactive bacterium in varnish) was established to study underlying mechanism. A steadily growing photocurrent (205 μA at 100 h) under light was observed with a stable birnessite after 110 h. However, only 47 μA was generated in the dark control and birnessite was reduced to Mn2+ in 13 h, suggesting that birnessite helped deliver electrons instead of serving as an electron acceptor under light. Our study demonstrated that electroactive bacterial communities were positively correlated with Fe/Mn semiconducting minerals in varnish, and diversified EET process occurred on varnish under sunlight. Overall, these phenomena may influence bacterial-community structure in natural environments over time.

Electrode Colonization by the Feammox Bacterium Acidimicrobiaceae sp. Strain A6

Most studies on electrogenic microorganisms have focused on the most abundant heterotrophs, while other microorganisms also commonly present in electrode microbial communities, such as Actinobacteria strains, have been overlooked. The novel Acidimicrobiaceae sp. strain A6 (Actinobacteria) is an iron-reducing bacterium that can colonize the surface of anodes in sediments and is linked to electrical current production, making it an electrode-reducing bacterium. Furthermore, A6 can carry out anaerobic ammonium oxidation coupled to iron reduction. Therefore, findings from this study open the possibility of using electrodes instead of iron as electron acceptors, as a means to promote A6 to treat NH₄⁺-containing wastewater more efficiently. Altogether, this study expands our knowledge of electrogenic bacteria and opens the possibility of developing Feammox-based technologies coupled to bioelectric systems for the treatment of NH₄⁺ and other contaminants in anoxic systems.

Acidimicrobiaceae sp. strain A6 (A6), from the Actinobacteria phylum, was recently identified as a microorganism that can carry out anaerobic ammonium (NH₄⁺) oxidation coupled to iron reduction, a process also known as Feammox. Being an iron-reducing bacterium, A6 was studied as a potential electrode-reducing bacterium that may transfer electrons extracellularly onto electrodes while gaining energy from NH₄⁺ oxidation. Actinobacteria species have been overlooked as electrogenic bacteria, and the importance of lithoautotrophic iron reducers as electrode-reducing bacteria at anodes has not been addressed. By installing electrodes in the soil of a forested riparian wetland where A6 thrives, in soil columns in the laboratory, and in A6-bioaugmented constructed wetland (CW) mesocosms and by operating microbial electrolysis cells (MECs) with pure A6 culture, the characteristics and performances of this organism as an electrode-reducing bacterium candidate were investigated. In this study, we show that Acidimicrobiaceae sp. strain A6, a lithoautotrophic bacterium, is capable of colonizing electrodes under controlled conditions. In addition, A6 appears to be an electrode-reducing bacterium, since current production was boosted shortly after the CWs were seeded with enrichment A6 culture and current production was detected in MECs operated with pure A6, with the anode as the sole electron acceptor and NH₄⁺ as the sole electron donor.

IMPORTANCE Most studies on electrogenic microorganisms have focused on the most abundant heterotrophs, while other microorganisms also commonly present in electrode microbial communities, such as Actinobacteria strains, have been overlooked. The novel Acidimicrobiaceae sp. strain A6 (Actinobacteria) is an iron-reducing bacterium that can colonize the surface of anodes in sediments and is linked to electrical current production, making it an electrode-reducing bacterium. Furthermore, A6 can carry out anaerobic ammonium oxidation coupled to iron reduction. Therefore, findings from this study open the possibility of using electrodes instead of iron as electron acceptors, as a means to promote A6 to treat NH₄⁺-containing wastewater more efficiently. Altogether, this study expands our knowledge of electrogenic bacteria and opens the possibility of developing Feammox-based technologies coupled to bioelectric systems for the treatment of NH₄⁺ and other contaminants in anoxic systems.

Enhancing the Electricity Generation and Nitrate Removal of Microbial Fuel Cells With a Novel Denitrifying Exoelectrogenic Strain EB-1

Microbial fuel cells (MFCs) have been tentatively applied for wastewater treatment, but the presence of nitrogen, especially nitrate, induces performance instability by changing the composition of functional biofilms. A novel denitrifying exoelectrogenic strain EB-1, capable of simultaneous denitrification and electricity generation and affiliated with Mycobacterium sp., was isolated from the anodic biofilm of MFCs fed with nitrate containing medium. Polarization curves and cyclic voltammetry showed that strain EB-1 could generate electricity through a direct electron transfer mechanism with a maximum power density of 0.84 ± 0.05 W m⁻². Additionally, anodic denitrification, as a concurrent metabolism, was demonstrated with an efficient removal rate of 0.66 ± 0.01 kg N m⁻³ d⁻¹ at a COD/N ratio of 3.5 ± 0.3. Importantly, voltage output was not negatively influenced by nitrate, indicating that the concurrent process of nitrate removal and electricity generation was a limitation of the electron donor rather than an inhibition of the system. Furthermore, various organic materials were successfully utilized as anode donors for strain EB-1, and demonstrated the exciting performances in terms of simultaneous denitrification and electricity generation. Mycobacterium sp. EB-1 thus expands the diversity of exoelectrogens and contributes to the potential applications of MFC for simultaneous energy recovery and wastewater treatment.

Biological Potential and Mechanism of Prodigiosin from Serratia marcescens Subsp. lawsoniana in Human Choriocarcinoma and Prostate Cancer Cell Lines

Tripyrrole molecules have received renewed attention due to reports of numerous biological activities, including antifungal, antibacterial, antiprotozoal, antimalarial, immunosuppressive, and anticancer activities. In a screen of bacterial strains with known toxicities to termites, a red pigment-producing strain, HDZK-BYSB107, was isolated from Chamaecyparis lawsoniana, which grows in Oregon, USA. Strain HDZK-BYSB107 was identified as Serratia marcescens subsp. lawsoniana. The red pigment was identified as prodigiosin using ultraviolet absorption, LC-MS, and 1H-NMR spectroscopy. The bacterial prodigiosin had an inhibitory effect on both Gram-negative and Gram-positive bacteria. The main objective of this study was to explore the anticancer activities and mechanism of strain HDZK-BYSB107 prodigiosin by using human choriocarcinoma (JEG3) and prostate cancer cell lines (PC3) in vitro and JEG3 and PC3 tumor-bearing nude mice in vivo. In vitro anticancer activities showed that the bacterial prodigiosin induced apoptosis in JEG3 cells. In vivo anticancer activities indicated that the prodigiosin significantly inhibited the growth of JEG3 and PC3 cells, and the inhibitory activity was dose and time dependent. The anticancer efficacy of the bacterial prodigiosin on JEG3 and PC3 cells, JEG3 and PC3 tumor exhibited a correlation with the down regulation of the inhibitor of IAP family, including XIAP, cIAP-1 and cIAP-2, and the activation of caspase-9 and caspase-3 accompanied by proteolytic degradation of poly (ADP-ribose)-polymerase. The expressions of P53 and Bax/Bcl-2 in JEG3 and PC3 cells were significantly higher than in untreated groups. Our results indicated that the bacterial prodigiosin extracted from C. lawsoniana is a promising molecule due to its potential for therapeutic applications.

Electro-Microbiology as a Promising Approach Towards Renewable Energy and Environmental Sustainability

Microbial electrochemical technologies provide sustainable wastewater treatment and energy production. Despite significant improvements in the power output of microbial fuel cells (MFCs), this technology is still far from practical applications. Extracting electrical energy and harvesting valuable products by electroactive bacteria (EAB) in bioelectrochemical systems (BESs) has emerged as an innovative approach to address energy and environmental challenges. Thus, maximizing power output and resource recovery is highly desirable for sustainable systems. Insights into the electrode-microbe interactions may help to optimize the performance of BESs for envisioned applications, and further validation by bioelectrochemical techniques is a prerequisite to completely understand the electro-microbiology. This review summarizes various extracellular electron transfer mechanisms involved in BESs. The significant role of characterization techniques in the advancement of the electro-microbiology field is discussed. Finally, diverse applications of BESs, such as resource recovery, and contributions to the pursuit of a more sustainable society are also highlighted.

Magnetotactic bacteria used to generate electricity based on Faraday's law of electromagnetic induction

Magnetotactic bacteria (MTB) have the unique ability to produce magnetic particles surrounded by a biomembrane to form the magnetosome organelle. Therefore, MTB have novel physical and magnetic properties and have consequently been used in several biotechnological applications. The magnetic properties of these micro-organisms and their magnetosomes have, however, never been used for the generation of electricity as described in this letter. Comparisons were made between, firstly, the electricity generated from purified magnetosomes, MTB culture (bacterial cells with magnetosomes) and sterile, liquid growth medium (control). Secondly, the electricity generated by a dilution series of purified magnetosomes were compared. A statistically significant difference was found between the voltage measured from the purified magnetosomes (highest voltage), MTB culture (lower voltage) and liquid growth medium (lowest voltage). In the dilution series, the voltage measured increased as the magnetosome concentration increased, but only up to an optimum concentration (0·0376 mg ml^-1 ). In this study, we have demonstrated that a significantly higher voltage than that of the control could be measured when MTB or purified magnetosomes were pumped through a solenoid by applying Faraday's law of electromagnetic induction.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides proof-of-concept of electromagnetic induction using magnetosomes or magnetotactic bacteria in an experimental setup based on the law of Faraday. The concept of using these bacteria or their biomineralized magnetic nanoparticles as a biological alternative in low voltage electricity generation has the potential to be further explored and developed.