Oneidensis MR-1 Research Articles

A rational designed synthetic three-species alliance system for synergetic improvement on power generation from microbial fuel cell

Microbial fuel cells with mixed bacteria always show better power output capacity than those with single bacteria due to synergetic effects between species. Here, a rational-designed synthetic three-species alliance system based on Shewanella oneidensis MR-1 (the model exoelectrogen), Pseudomonas aeruginosa, and Lactobacillus plantarum was constructed upon process optimization, the three-species alliance system in MFC delivered a maximum power density of ∼ 207 mW/m2 by using the glucose as the substrate, which was 2 ∼ 58 times higher than that of MFC inoculated with single species. In addition, the synthetic alliance system could generate electricity from broad substrate spectrum (lactose, saccharose, maltose, arabinose, cellobiose) with enhanced performance. Electrochemical and metabolism analysis indicated inter-species synergetic enhancement on charge transfer, substrate utilization, and biofilm formation was the underlying mechanism for performance improvement in MFC by this synthetic alliance system. In this system, L. plantarum uses glucose to produce lactic acid as the electrogenic substrate and electron donor of S. oneidensis MR-1, and P. aeruginosa uses glucose to produce another electron shuttle phenazine, which can also promote the growth of S. oneidensis MR-1 biofilm and help the alliance system to transfer electrons better. This work demonstrated a new strategy to enhance the MFC performance with a rational designed synthetic bacterial community, which would further renew the toolbox for MFC optimization.

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.

DIET-like and MIET-like mutualism of S. oneidensis MR-1 and metal-reducing function microflora boosts Cr(VI) reduction

Microbial treatment of Cr(VI) is an environmentally friendly and low-cost approach. However, the mechanism of mutualism and the role of interspecies electron transfer in Cr(VI) reducing microflora are unclear. Herein, we constructed an intersymbiotic microbial association flora to augment interspecies electron transfer via functionalizing electroactive Shewanella oneidensis MR-1 with metal-reducing microflora, and thus the efficiency of Cr(VI) reduction. The findings suggest that the metal-reducing active microflora could converts glucose into lactic acid and riboflavin for S. oneidensis MR-1 to act as a carbon source and electron mediator. Thus, when adding initial 25 mg/L Cr (VI), this microflora exhibited an outstanding Cr (VI) removal efficiency (100%) at 12 h and elevated Cr (III) immobilization efficiency (80%) at 60 h with the assistance of 25 mg/L Cu(II). A series of electrochemical experiments proved this remarkable removal efficiency were ascribed to the improved interspecies electron transfer efficiency through direct interspecies electron transfer and riboflavin through mediated interspecies electron transfer. Furthermore, the metagenomic analysis revealed the expression level of the electron transport pathway was promoted. Intriguing high abundance of genes participating in the bio-reduction and biotransformation of Cr(VI) was also observed in functional microflora. These outcomes give a novel strategy for enhancing the reduction and fixation of harmful heavy metals by coculturing function microflora with electrogenic microorganisms.

Co-metabolic degradation and metabolite detection of hexabromocyclododecane by Shewanella oneidensis MR-1.

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant; however, it is a persistent organic pollutant as well as affects the human thyroid hormones and causes cancer. However, the degradation of HBCD has received little attention from researchers. Due to its bioaccumulative and hazardous properties, an appropriate strategy for its remediation is required. In this study, we investigated the biodegradation of HBCD using Shewanella oneidensis MR-1 under optimized conditions. The Box-Behnken design (BBD) was implemented for the optimization of the physical degradation parameters of HBCD. S. oneidensis MR-1 showed the best degradation performance at a temperature of 30 °C, pH 7, and agitation speed of 115 rpm, with an HBCD concentration of 1125 μg/L in mineral salt medium (MSM). The strain tolerated up to 2000 μg/L HBCD. Gas chromatography-mass spectrometry analysis identified three intermediates, including 2-bromo dodecane, 2,7,10-trimethyldodecane, and 4-methyl-1-decene. The results provide an insightful understanding of the biodegradation of HBCD by S. oneidensis MR-1 under optimized conditions and could pave the way for further eco-friendly applications. KEY POINTS: • HBCD biodegradation by Shewanella oneidensis • Optimization of HBCD biodegradation by the Box-Behnken analysis • Identification of useful metabolites from HBCD degradation.

Acetylation of xenogeneic silencer H-NS regulates biofilm development through the nitrogen homeostasis regulator in Shewanella.

Adjusting intracellular metabolic pathways and adopting suitable live state such as biofilms, are crucial for bacteria to survive environmental changes. Although substantial progress has been made in understanding how the histone-like nucleoid-structuring (H-NS) protein modulates the expression of the genes involved in biofilm formation, the precise modification that the H-NS protein undergoes to alter its DNA binding activity is still largely uncharacterized. This study revealed that acetylation of H-NS at Lys19 inhibits biofilm development in Shewanella oneidensis MR-1 by downregulating the expression of glutamine synthetase, a critical enzyme in glutamine synthesis. We further found that nitrogen starvation, a likely condition in biofilm development, induces deacetylation of H-NS and the trimerization of nitrogen assimilation regulator GlnB. The acetylated H-NS strain exhibits significantly lower cellular glutamine concentration, emphasizing the requirement of H-NS deacetylation in Shewanella biofilm development. Moreover, we discovered in vivo that the activation of glutamine biosynthesis pathway and the concurrent suppression of the arginine synthesis pathway during both pellicle and attached biofilms development, further suggesting the importance of fine tune nitrogen assimilation by H-NS acetylation in Shewanella. In summary, posttranslational modification of H-NS endows Shewanella with the ability to respond to environmental needs by adjusting the intracellular metabolism pathways.

3D Printed Carbon Framework with the Graphene Aerogel for Microbial Fuel Cell Application

There is a high interest in living organism-compatible materials associated with electrically active interfaces. Bacteria/electrode interfaces implement smart, functional systems with responses, based on which it is possible to elaborate self-regulating energy generation systems. Carbon materials have a number of advantages, such as biocompatibility, low electrical resistance, and the possibility of increasing the electrode surface on an industrial scale. The most promising approach for the industrial production of electrodes is 3D printing. We propose a 3D-printed carbon electrode – a novel lightweight material for electrodes in bioelectrochemical systems for efficient bioelectricity utilization.The pyrolytic process for manufacturing carbon electrodes is promising for upscaling and industrial applications. However, there is a problem of volume loss when 3D-printed polymers are pyrolyzed in an inert environment. We propose a new strategy for the thermal treatment of 3D-printed polymers that allow for reduced volume loss under pyrolytic carbonization. In addition, to achieve a higher electrode surface area, the graphene aerogel could be impregnated into the 3D-printed scaffolds. Chemical modification of graphene surface can enhance biocompatibility. Specifically, the oxidation of graphene leads to forming a hydrophilic and biocompatible material. We tune graphene hydrophilic properties and electrical conductivity via control over the thermal reduction of the oxidized form of graphene–graphene oxide1.Such sponge morphology affords 3D-printed carbon scaffolds an excellent lightweight host scaffold for microorganisms, in which the graphene nanowalls are homogeneously occupied by S. oneidensis MR-1. We demonstrate a novel sustainable method to produce graphene-based lightweight 3D printed electrode materials for green energy production from biomass. The proposed technology creates the opportunity for novel, innovative, disruptive graphene applications that can lead to the establishment of new energy-related industries and facilitate many startups in the ecosystem. Acknowledgments This work was supported by the Ministry of Education (Singapore) through the Research Centre of Excellence program (grant EDUN C-33-18-279-V12, I-FIM). References Xuanye Leng, Ricardo J. Vazquez, Samantha R. McCuskey, Glenn Quek, Yude Su, Konstantin G. Nikolaev, Mariana C.F. Costa, Siyu Chen, Musen Chen, Kou Yang, Jinpei Zhao, Mo Lin, Zhaolong Chen, Guillermo C. Bazan, Kostya S. Novoselov, Daria V. Andreeva, Carbon, 205, 2023, 33-39.

The electron transport chain of Shewanella oneidensis MR-1 can operate bidirectionally to enable microbial electrosynthesis.

Extracellular electron transfer is a process by which bacterial cells can exchange electrons with a redox-active material located outside of the cell. In Shewanella oneidensis, this process is natively used to facilitate respiration using extracellular electron acceptors such as Fe(III) or an anode. Previously, it was demonstrated that this process can be used to drive the microbial electrosynthesis (MES) of 2,3-butanediol (2,3-BDO) in S. oneidensis exogenously expressing butanediol dehydrogenase (BDH). Electrons taken into the cell from a cathode are used to generate NADH, which in turn is used to reduce acetoin to 2,3-BDO via BDH. However, generating NADH via electron uptake from a cathode is energetically unfavorable, so NADH dehydrogenases couple the reaction to proton motive force. We therefore need to maintain the proton gradient across the membrane to sustain NADH production. This work explores accomplishing this task by bidirectional electron transfer, where electrons provided by the cathode go to both NADH formation and oxygen (O2) reduction by oxidases. We show that oxidases use trace dissolved oxygen in a microaerobic bioelectrical chemical system (BES), and the translocation of protons across the membrane during O2 reduction supports 2,3-BDO generation. Interestingly, this process is inhibited by high levels of dissolved oxygen in this system. In an aerated BES, O2 molecules react with the strong reductant (cathode) to form reactive oxygen species, resulting in cell death.IMPORTANCEMicrobial electrosynthesis (MES) is increasingly employed for the generation of specialty chemicals, such as biofuels, bioplastics, and cancer therapeutics. For these systems to be viable for industrial scale-up, it is important to understand the energetic requirements of the bacteria to mitigate unnecessary costs. This work demonstrates sustained production of an industrially relevant chemical driven by a cathode. Additionally, it optimizes a previously published system by removing any requirement for phototrophic energy, thereby removing the additional cost of providing a light source. We also demonstrate the severe impact of oxygen intrusion into bioelectrochemical systems, offering insight to future researchers aiming to work in an anaerobic environment. These studies provide insight into both the thermodynamics of electrosynthesis and the importance of the bioelectrochemical systems' design.

Investigation on the effect of Cu2+, Mn2+ and Fe3+ on biotreatment of Cr(VI) by Shewanella oneidensis and Bacillus subtilis in bimetallic system

Coexistence of chromium and iron, manganese and copper in industries is common, which may affect the microbial treating efficiency and toxicity to microorganisms, thus restricting the application of microbial treatment technology. In this research, Cu2+ promoted the reduction of Cr(VI) and the fixation of total chromium in bimetallic systems for both Shewanella oneidensis MR-1 and Bacillus subtilis, while Mn2+ and Fe3+ exhibited inhibition effects. Generally, groups with coexisting heavy metal of 0.1 mM were most affected, no matter promotive or inhibitive. Toxicity analysis revealed that high concentration of heavy metal ions led to damage to the cell membranes and reduction of their survival rate. To clarify the optimal condition for microbial treatment, response surface methodology was used to investigate the influencing factors of Cr(VI) reduction by S. oneidensis. The total chromium concentration in the supernatant was correlated with three factors, and the significant order of influence was: culture time > culture temperature > pH.

An oral bacterial pyroptosis amplifier against malignant colon cancer

The oncolytic microbe can trigger pyroptotic cancer cell death, but insufficient pyroptotic response of current microbe-based biotherapeutics restricts the antitumor efficiency. Herein, we report an oral bacterial pyroptosis amplifier composed of two bacterial strains, reductive Shewanella oneidensis MR-1 (abbreviated as MR-1) and engineered Escherichia coli (E. coli) with the overexpression of pyranose oxidase, augmenting the pyroptosis effect against colon and metastatic tumors. Each bacterium is camouflaged with hyaluronic acid to survive against the harsh gastrointestinal environment and to enrich in colon tumor sites. Upon the bacteria colonizing at the tumor site, iron sucrose is orally administrated. The following oral administration of Fe(Ⅲ)-contained iron sucrose leads to the intratumoral accumulation of Fe(Ⅱ) by the reduction characteristic of MR-1. Hydrogen peroxide (H2O2), synthesized by pyranose oxidase from E. coli, serves as the substrate for Fenton reaction to generate toxic hydroxyl radicals through Fe(Ⅱ)-H2O2-Fe(Ⅲ) recycling between both strains, thereby promoting immunogenic pyroptosis inside the tumor. This can potentiate lymphocyte activation in the gastrointestinal tissues, exerting significant therapeutic efficacy in multiple colon metastatic tumor models. This study offers promising insight into developing future microbe biotherapeutics with enhanced pyroptosis activity in cancer immunotherapy.

Engineering artificial photosynthesis based on rhodopsin for CO2 fixation

Microbial rhodopsin, a significant contributor to sustaining life through light harvesting, holds untapped potential for carbon fixation. Here, we construct an artificial photosynthesis system which combines the proton-pumping ability of rhodopsin with an extracellular electron uptake mechanism, establishing a pathway to drive photoelectrosynthetic CO2 fixation by Ralstonia eutropha (also known as Cupriavidus necator) H16, a facultatively chemolithoautotrophic soil bacterium. R. eutropha is engineered to heterologously express an extracellular electron transfer pathway of Shewanella oneidensis MR-1 and Gloeobacter rhodopsin (GR). Employing GR and the outer-membrane conduit MtrCAB from S. oneidensis, extracellular electrons and GR-driven proton motive force are integrated into R. eutropha’s native electron transport chain (ETC). Inspired by natural photosynthesis, the photoelectrochemical system splits water to supply electrons to R. eutropha via the Mtr outer-membrane route. The light-activated proton pump - GR, supported by canthaxanthin as an antenna, powers ATP synthesis and reverses the ETC to regenerate NADH/NADPH, facilitating R. eutropha’s biomass synthesis from CO2. Overexpression of a carbonic anhydrase further enhances CO2 fixation. This artificial photosynthesis system has the potential to advance the development of efficient photosynthesis, redefining our understanding of the ecological role of microbial rhodopsins in nature.

Effects of Reduction Methods on the Performance of Shewanella oneidensis MR-1 Palladium/Carbon Catalyst for Oxygen Reduction Reaction.

The influence of the reduction method on the morphology and performance of the catalyst still controversial. In this study, hydrogen, Shewanella oneidensis MR-1 (MR-1), MR-1 and hydrogen coreduction are used to reduce the palladium ions adsorbed by MR-1 to obtain Pd/CH2, Pd/CM, and Pd/CH2+M catalyst, respectively. It is found that the palladium nanoparticles (Pd NPs) in Pd/CH2+M are the largest, while the Pd NPs in Pd/CM are the smallest. This is due to the reduction of Pd NPs in Pd/CH2+M under anaerobic conditions to form smaller Pd NPs that will further aggregate and grow in H2. In addition, Pd/CM exhibited the best catalytic performance with a mass activity of 0.31 A mg-1, better than that of Pd/CH2 (0.06 A mg-1) and Pd/CH2+M (0.13 A mg-1). This study provides a meaningful reference for the selection of reduction methods in metal catalysts.

Long-term continuous degradation of carbon nanotubes by a bacteria-driven Fenton reaction

Very few bacteria are known that can degrade carbon nanotubes (CNTs), and the only known degradation mechanism is a Fenton reaction driven by Labrys sp. WJW with siderophores, which only occurs under iron-deficient conditions. No useful information is available on the degradation rates or long-term stability and continuity of the degradation reaction although several months or more are needed for CNT degradation. In this study, we investigated long-term continuous degradation of oxidized (carboxylated) single-walled CNTs (O-SWCNTs) using bacteria of the genus Shewanella. These bacteria are widely present in the environment and can drive the Fenton reaction by alternating anaerobic-aerobic growth conditions under more general environmental conditions. We first examined the effect of O-SWCNTs on the growth of S. oneidensis MR-1, and it was revealed that O-SWCNTs promote growth up to 30 μg/mL but inhibit growth at 40 μg/mL and above. Then, S. oneidensis MR-1 was subjected to incubation cycles consisting of 21-h anaerobic and 3-h aerobic periods in the presence of 30 μg/mL O-SWCNTs and 10 mM Fe(III) citrate. We determined key factors that help prolong the bacteria-driven Fenton reaction and finally achieved long-term continuous degradation of O-SWCNTs over 90 d. By maintaining a near neutral pH and replenishing Fe(III) citrate at 60 d, a degraded fraction of 56.3% was reached. S. oneidensis MR-1 produces Fe(II) from Fe(III) citrate, a final electron acceptor for anaerobic respiration during the anaerobic period. Then, ·OH is generated through the Fenton reaction by Fe(II) and H2O2 produced by MR-1 during the aerobic period. ·OH was responsible for O-SWCNT degradation, which was inhibited by scavengers of H2O2 and ·OH. Raman spectroscopy and X-ray photoelectron spectroscopy showed that the graphitic structure in O-SWCNTs was oxidized, and electron microscopy showed that long CNT fibers initially aggregated and became short and isolated during degradation. Since Shewanella spp. and iron are ubiquitous in the environment, this study suggests that a Fenton reaction driven by this genus is applicable to the degradation of CNTs under a wide range of conditions and will help researchers develop novel methods for waste treatment and environmental bioremediation against CNTs.

Characterising ATP binding activity of PilB ATPase of Shewanella oneidensis MR-1 using a molecular modeling and simulations approach

Characterising ATP binding activity of PilB ATPase of Shewanella oneidensis MR-1 using a molecular modeling and simulations approach

Abiotic and Biotic Reduction of Iodate Driven by Shewanella oneidensis MR-1.

Iodate (IO3-) can be abiotically reduced by Fe(II) or biotically reduced by the dissimilatory Fe(III)-reducing bacterium Shewanella oneidensis (MR-1) via its DmsEFAB and MtrCAB. However, the intermediates and stoichiometry between the Fe(II) and IO3- reaction and the relative contribution of abiotic and biotic IO3- reduction by biogenic Fe(II) and MR-1 in the presence of Fe(III) remain unclear. In this study, we found that abiotic reduction of IO3- by Fe(II) produced intermediates HIO and I- at a ratio of 1:2, followed by HIO disproportionation to I- and IO3-. Comparative analyses of IO3- reduction by MR-1 wild type (WT), MR-1 mutants deficient in DmsEFAB or MtrCAB, and Shewanella sp. ANA-3 in the presence of Fe(III)-citrate, Fe(III) oxides, or clay minerals showed that abiotic IO3- reduction by biogenic Fe(II) predominated under iron-rich conditions, while biotic IO3- reduction by DmsEFAB played a more dominant role under iron-poor conditions. Compared to that in the presence of Fe(III)-citrate, MR-1 WT reduced more IO3- in the presence of Fe(III) oxides and clay minerals. The observed abiotic and biotic IO3- reduction by MR-1 under Fe-rich and Fe-limited conditions suggests that Fe(III)-reducing bacteria could contribute to the transformation of iodine species and I- enrichment in natural iodine-rich environments.

Enhanced azo dye reduction at semiconductor-microbe interface: The key role of semiconductor band structure

Low-energy environmental remediation could be achieved by biocatalysis with assistance of light-excited semiconductor, in which the energy band structure of semiconductor has a significant influence on the metabolic process and electron transfer of microbes. In this study, direct Z-scheme and type II heterojunction semiconductor with different energy band structure were successfully synthesized for constructing semiconductor-microbe interface with Shewanella oneidensis MR-1 to achieve acid orange7 (AO7) biodegradation. UV–vis diffuse reflection spectroscopy, photoluminescence spectra and photoelectrochemical analysis revealed that the direct Z-scheme heterojunction semiconductor had stronger reduction power and faster separation of photoelectron-hole, which was beneficial for the AO7 biodegradation at semiconductor-microbe interface. Riboflavin was also involved in electron transfer between the semiconductor and microbes during AO7 reduction. Transcriptome results illustrated that functional gene expression of Shewanella oneidensis MR-1 was upregulated significantly with photo-stimulation of direct Z-scheme semiconductor, and Mtr pathway and conductive pili played the important roles in the photoelectron utilization by Shewanella oneidensis MR-1. This work is expected to provide alternative ideas for designing semiconductor-microbial interface with efficient electron transfer and broadening their applications in bioremediation.

Improved microbial reduction of biogenic and abiogenic goethite by diesel soot

The biogeochemical cycling of iron is crucial to plenty of environmental processes, and is often influenced by black carbon with high electrical conductivity and abundant functional groups. This study for the first time revealed that diesel particulate matter (DPM), a typical black carbon material which often caused serious environmental effects, could significantly promote dissimilatory reduction of both abiogenic and biogenic goethite (CGt and BGt) by Shewanella oneidensis MR-1. In 7 days, Fe(II) production in CGt systems containing 0.5, 5, 10, 25, and 50 mg/L of DPM were 1.2, 1.3, 1.8, 1.9, and 2.7 folds higher than that in the system without DPM (0.12 mM), respectively. During the bioreduction of BGt, Fe(II) concentrations were 2.4–3.4 folds higher than those in the CGt systems, and were increased by 4.8%− 41.7% with the addition of 0.5–50 mg/L DPM. X-ray diffraction (XRD) analysis demonstrated that goethite was the sole mineralized product during the bioreduction of CGt, while vivianite appeared gradually during the microbial transformation of BGt. DPM enhanced electron transfer between cells and goethite via serving as electron shuttles. The results of this study would improve our understanding of interactions among microbes, natural minerals, and black carbon in the natural environments.

The Effects of Aniline-Promoted Electron Shuttle-Mediated Goethite Reduction by Shewanella oneidensis MR-1 and theDegradation of Aniline

The biological reduction of Fe (III) is common in underground environments. This process not only affects the biogeochemical cycle of iron but also influences the migration and transformation of pollutants. Humic substances are considered effective strategies for improving the migration and transformation of toxic substances and enhancing the bioavailability of Fe (III). In this study, the electron shuttle anthraquinone-2-sulfonate (AQS) significantly promoted the bio-reduction of Fe (III). On this basis, different concentrations of aniline were added. The research results indicate that at an aniline concentration of 3 μM, the production of Fe (II) in the reaction system was 2.51 times higher compared to the microbial reaction group alone. Furthermore, the degradation of aniline was most effective in this group. The increased consumption of sodium lactate suggests that aniline, under the mediation of AQS, promoted the metabolism of Shewanella oneidensis MR-1 cells and facilitated the involvement of more electrons in the reduction process. After the reaction, the solid mineral Fe (II)-O content increased to 41.32%. This study provides insights into the reduction mechanism of Fe (III) in the complex environment of microorganisms, iron minerals, electron shuttles, and pollutants. It aims to offer a theoretical basis for the biodegradation of aromatic hydrocarbon pollutants.

Bacterial extracellular electron transfer components are spin selective.

Metal-reducing bacteria have adapted the ability to respire extracellular solid surfaces instead of soluble oxidants. This process requires an electron transport pathway that spans from the inner membrane, across the periplasm, through the outer membrane, and to an external surface. Multiheme cytochromes are the primary machinery for moving electrons through this pathway. Recent studies show that the chiral-induced spin selectivity (CISS) effect is observable in some of these proteins extracted from the model metal-reducing bacteria, Shewanella oneidensis MR-1. It was hypothesized that the CISS effect facilitates efficient electron transport in these proteins by coupling electron velocity to spin, thus reducing the probability of backscattering. However, these studies focused exclusively on the cell surface electron conduits, and thus, CISS has not been investigated in upstream electron transfer components such as the membrane-associated MtrA, or periplasmic proteins such as small tetraheme cytochrome (STC). By using conductive probe atomic force microscopy measurements of protein monolayers adsorbed onto ferromagnetic substrates, we show that electron transport is spin selective in both MtrA and STC. Moreover, we have determined the spin polarization of MtrA to be ∼77% and STC to be ∼35%. This disparity in spin polarizations could indicate that spin selectivity is length dependent in heme proteins, given that MtrA is approximately two times longer than STC. Most significantly, our study indicates that spin-dependent interactions affect the entire extracellular electron transport pathway.

Enhancement of microbial current production by riboflavin requires the reduced heme centers in outer membrane cytochromes in Shewanella oneidensis MR-1

Enhancement of microbial current production by riboflavin requires the reduced heme centers in outer membrane cytochromes in Shewanella oneidensis MR-1

An in-field assembled hierarchical mesoporous electroenzymatic sensor for sensitive and real-time monitoring of nitrite

Electroenzymatic sensors are promising for nitrite detection but their application in real environmental scenarios is restricted due to the challenges in fabrication complexity and storage stability. Herein, we proposed a “drop & go” strategy to allow non-professionals to fabricate the electroenzymatic sensors in-field for monitoring the nitrite in real-time. To achieve this, hierarchical mesoporous ITO (mesoITO) electrode was prepared via a sol-gel process and a nitrite reductase NrfA originated from Shewanella oneidensis MR-1 was immobilized via a simple dropping process. Cyclic voltammetric (CV) analyses confirmed the direct electron transfer between NrfA and mesoITO electrode. After optimizing the enzyme dosage and electrochemical parameters, both CV and amperometric assays for nitrite detection were developed and a linear detection range of 10–130 μM and 1–140 μM nitrite were determined, respectively. Besides, these electroenzymatic sensors exhibited excellent resistance to the common anions in the water and good performance stability under working conditions. With this basis, the fabricated biosensors were applied for continuously monitoring the nitrite in a denitrifying process and the results were well-matched with the colorimetric method reference. More importantly, the presence of bacterial cells created favorable microenvironment for electroenzymatic nitrite reduction, and promoted the detection of trace nitrite in the bioreactor. This work developed a new methodology for fast electroenzymatic biosensor assembling, facilitate sensitive nitrite quantification in the real environment scenario, and may bring new concept for environment contaminants monitoring in real-time.