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• The combination of natural microbe species enhanced both direct and indirect electron transport mechanisms. • The alliance system expands the utilization spectra of the carbon source. • Riboflavin and Phenazine two electron shuttles work in coordination. 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. [ABSTRACT FROM AUTHOR]

Biological synthesis of green nanomaterials holds great promise for sustainable catalysis with versatile applications. Herein, Shewanella oneidensis MR‐1 is used to develop a green method to synthesize Pd/reductive graphene oxide (rGO) nanocomposites without the addition of toxic reducing agents. It was found that S. oneidensis MR‐1 cells could efficiently reduce graphene oxide to rGO and synthesize Pd nanoparticles that uniformly dispersed on the rGO nanosheets. More strikingly, the addition of GO greatly increases the recovery rate of Pd from 37.8 % to 90.4 %. After carbonization, the biosynthesized Pd/rGO nanocomposites exhibits promising catalytic activities toward oxygen reduction reaction with an onset potential of 0.92 V, a half‐wave potential of 0.81 V, and a limiting current density of 5.2 mA cm−2 in 0.1 M KOH electrolyte. This work provides a simple, "green", and cost‐effective method for the preparation of graphene supported nanocomposites with extended applications. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) macroporous reduced graphene oxide/polypyrrole (rGO/Ppy) hydrogel assembled by bacterial cells was fabricated and applied for microbial fuel cells. By taking the advantage of electroactive cell-induced bioreduction of graphene oxide and in-situ polymerization of Ppy, a facile self-assembly by Shewanella oneidensis MR-1and in-situ polymerization approach for 3D rGO/Ppy hydrogel preparation was developed. This facile one-step self-assembly process enabled the embedding of living electroactive cells inside the hydrogel electrode, which showed an interconnected 3D macroporous structures with high conductivity and biocompatibility. Electrochemical analysis indicated that the self-assembly of cell-embedding rGO/Ppy hydrogel enhanced the electrochemical activity of the bioelectrode and reduced the electron charge transfer resistance between the cells and the electrode. Impressively, extremely high power output of 3366 ± 42 mW m−2 was achieved from the MFC with cell-embedding rGO/Ppy hydrogel rGO/Ppy, which was 8.6 times of that delivered from the MFC with bare electrode. Further analysis indicated that the increased cell loading by the hydrogel and improved electrochemical activity by the rGO/Ppy composite would be the underlying mechanism for this performance improvement. This study provided a facile approach to fabricate the biocompatible and electrochemical active 3D nanocomposites for MFC, which would also be promising for performance optimization of various bioelectrochemical systems. [Display omitted] • Cell-embedding rGO/Ppy hydrogel was assembled by bacterial cells. • The biohydrogel showed high cell viability and excellent electrochemical activity. • Efficient extracellular electron transfer between cell and electrode was achieved. • Extremely high power output of 3366 ± 42 mW m−2 was achieved from the MFC. [ABSTRACT FROM AUTHOR]

Whole-cell biosensors are an important class of analytical tools that offer the advantages of low cost, facile operation, and unique reproduction/regeneration ability. However, it has always been quite challenging to expand the sensing spectrum of the host. Here, a new approach to extend the cell sensing spectrum with biomineralized nanoparticles is developed. The nano-biohybrid design comprise biomineralized FeS nanoparticles firmly anchored onto the bacterium, Shewanella oneidensis MR-1, wherein the nanoparticles are wired to the cellular electron transfer machinery (MtrCAB/OmcA) of the bacterium, forming an artificial cyborgian redox machinery consisting of FeS-MtrCAB/OmcA-FccA. Strikingly, with this cyborgian redox machinery, the sensing spectrum of FeS hybridized S. oneidensis MR-1 cell is successfully expanded to enable whole-cell electrochemical detection of Vitamin B12, while an unhybridized native cell is incapable of sensing. This proof-of-concept nano-biohybrid design offers a new perspective on manipulating the microbial toolkit for an expanded sensing spectrum in whole-cell biosensors. [Display omitted] • A nano-hybridized electroactive bacteria based system was assembled. • Artificial cyborgian redox machinery was identified in this biohybrid cell. • This cyborgian redox machinery expanded the sensing spectrum of Shewanella cell. • A sensitive whole-cell biosensing system for VB12 was developed. [ABSTRACT FROM AUTHOR]

Toxicity assessment of water is of great important to the safety of human health and to social security because of more and more toxic compounds that are spilled into the aquatic environment. Therefore, the development of fast and reliable toxicity assessment methods is of great interest and attracts much attention. In this study, by using the electrochemical activity of Shewanella oneidensis MR-1 cells as the toxicity indicator, 3,5-dichlorophenol (DCP) as the model toxic compound, a new biosensor for water toxicity assessment was developed. Strikingly, the presence of DCP in the water significantly inhibited the maximum current output of the S. oneidensis MR-1 in a three-electrode system and also retarded the current evolution by the cells. Under the optimized conditions, the maximum current output of the biosensor was proportional to the concentration of DCP up to 30 mg/L. The half maximal inhibitory concentration of DCP determined by this biosensor is about 14.5 mg/L. Furthermore, simultaneous monitoring of the retarded time (Δ t) for current generation allowed the identification of another biosensor signal in response to DCP which could be employed to verify the electrochemical result by dual confirmation. Thus, the present study has provided a reliable and promising approach for water quality assessment and risk warning of water toxicity. [ABSTRACT FROM AUTHOR]

Toxicity assessment of water is of great important to the safety of human health and to social security because of more and more toxic compounds that are spilled into the aquatic environment. Therefore, the development of fast and reliable toxicity assessment methods is of great interest and attracts much attention. In this study, by using the electrochemical activity of Shewanella oneidensis MR-1 cells as the toxicity indicator, 3,5-dichlorophenol (DCP) as the model toxic compound, a new biosensor for water toxicity assessment was developed. Strikingly, the presence of DCP in the water significantly inhibited the maximum current output of the S. oneidensis MR-1 in a three-electrode system and also retarded the current evolution by the cells. Under the optimized conditions, the maximum current output of the biosensor was proportional to the concentration of DCP up to 30 mg/L. The half maximal inhibitory concentration of DCP determined by this biosensor is about 14.5 mg/L. Furthermore, simultaneous monitoring of the retarded time (Δ t) for current generation allowed the identification of another biosensor signal in response to DCP which could be employed to verify the electrochemical result by dual confirmation. Thus, the present study has provided a reliable and promising approach for water quality assessment and risk warning of water toxicity. [ABSTRACT FROM AUTHOR]

A novel whole-cell electrochemical sensor was developed and applied for sensitive amperometric detection of riboflavin. In this work, a whole-cell based riboflavin redox cycling system was characterized, in which electroactive bacteria Shewanella oneidensis MR-1 was employed as the biocatalyst to regenerate the reduced riboflavin after the electrode oxidation. This redox cycling system efficiently enhanced the electrochemical response of riboflavin and enabled a stable current output at poised electrode potential. Thus, a sensitive amperometric biosensing system for riboflavin detection was developed by integrating this whole-cell redox cycling system with the conventional riboflavin electrochemical sensor. Remarkably, this riboflavin biosensor exhibited high sensitivity (LOD = 0.85 ± 0.09 nM, S/N = 3), excellent selectivity and stability. Additionally, reliable analysis of real samples (food and pharmaceutical samples) by this biosensor was achieved. This work provided sensitive and practical tool for riboflavin detection, and demonstrated that the integration of electroactive bacteria and using its outwards electron transfer for redox cycling would be a powerful and promising strategy to improve the performance of electrochemical sensing system. [ABSTRACT FROM AUTHOR]

Although microbial fuel cells (MFCs) is considered as one of the most promising technology for renewable energy harvesting, low power output still accounts one of the bottlenecks and limits its further development. In this work, it is found that Cu 2+ (0.1 μg L −1 –0.1 mg L −1 ) or Cd 2+ (0.1 μg L −1 –1 mg L −1 ) significantly improve the electricity generation in MFCs. The maximum power output achieved with trace level of Cu 2+ (∼6 nM) or Cd 2+ (∼5 nM) is 1.3 times and 1.6 times higher than that of the control, respectively. Further analysis verifies that addition of Cu 2+ or Cd 2+ effectively improves riboflavin production and bacteria attachment on the electrode, which enhances bacterial extracellular electron transfer (EET) in MFCs. These results unveil the mechanism for power output enhancement by Cu 2+ or Cd 2+ addition, and suggest that metal ion addition should be a promising strategy to enhance EET as well as power generation of MFCs. [ABSTRACT FROM AUTHOR]

Biologically synthesized palladium nanoparticles (bio-Pd) have attracted considerable interest as promising green catalysts for environmental remediation. However, the mechanisms by which microorganisms produce bio-Pd remain unclear. In the present study, we investigated the roles of Shewanella oneidensis MR-1 and its NADH dehydrogenases and hydrogenases (HydA and HyaB) in bio-Pd production using formate as the electron donor. The roles of NADH dehydrogenases and hydrogenases were studied by inhibiting NADH dehydrogenases and using hydrogenase mutants (Δ hydA , Δ hyaB , and Δ hydA Δ hyaB), respectively. The results showed ~97% reduction of palladium by S. oneidensis MR-1 after 24 h using 250 μM palladium and 500 μM formate. Electron microscopy images showed the presence of bio-Pd on both the outer and cytoplasmic membranes of S. oneidensis MR-1. However, the inhibition of NADH dehydrogenases in S. oneidensis MR-1 resulted in only ~61% reduction of palladium after 24 h, and bio-Pd were not found on the outer membrane. The mutants lacking one or two hydrogenases removed 91–96% of palladium ions after 24 h and showed more cytoplasmic bio-Pd but less periplasmic bio-Pd. To the best of our knowledge, this is the first study to demonstrate the role of NADH dehydrogenases of S. oneidensis MR-1 in the formation of bio-Pd on the outer membrane. It also demonstrates that the hydrogenases (especially HyaB) of S. oneidensis MR-1 contribute to the formation of bio-Pd in the periplasmic space. This study provides mechanistic insights into the production of biogenic metal nanoparticles towards their possible use in industrial and environmental applications. • S. oneidensis MR-1 deposited bio-Pd on both the outer and cytoplasmic membranes. • The inhibition of NADH dehydrogenases in S. oneidensis MR-1 significantly slowed down the Pd(II) reduction. • The NADH dehydrogenases in S. oneidensis MR-1 participated in the formation of bio-Pd on the outer membrane. • The hydrogenase mutants of S. oneidensis MR-1 produced less periplasmic bio-Pd and more cytoplasmic bio-Pd. • The hydrogenases in S. oneidensis MR-1 promoted the formation of bio-Pd in the periplasmic space. [ABSTRACT FROM AUTHOR]