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Highlights: [•] A new immobilization method for electrogenic microorganism was developed. [•] The conductive granules significantly decreased the internal resistance of MFC. [•] Higher coulombic efficiency and salt tolerance were achieved with this new method. [Copyright &y& Elsevier]

Direct interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR‐1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell‐cell click chemistry strategy. By introducing alkyne‐ or azide‐modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C‐type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell‐cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications. [ABSTRACT FROM AUTHOR]

Abstract: Electrolyte pH tremendously affects the electricity output of microbial fuel cells. However, its underlying molecular mechanism remains elusive, in particular for Shewanella oneidensis MR-1, one of the most widely adopted electrogenic microorganisms. Herein, we found that MFCs were able to deliver a significant (but different) electricity output in a wide range of pH (from 6 to 10), with the maximum at pH=9 (alkaline), which delivers ∼1.5times’ higher power output than that at pH=7 (neutral). Furthermore, cyclic voltammetry analysis showed an enhanced electrochemical activity of riboflavin (responsible for extracellular electron transfer of Shewanella) at alkaline pH. Strikingly, the concentration of riboflavin synthesized by Shewanella in MFCs at different pH showed a good correlation with the electricity output of MFCs. Thus, our results substantiated that the increase of riboflavin biosynthesis by Shewanella at the alkaline condition underlies the improvement of the electricity output in MFCs. [Copyright &y& Elsevier]

Nitrogen doped carbon nanoparticles (NDCN) were applied to modify the carbon cloth anodes of microbial fuel cells (MFCs) inoculated with Shewanella oneidensis MR-1, one of the most well-studied exoelectrogens. Experimental results demonstrated that the use of NDCN increased anodic absorption of flavins ( i.e. , the soluble electron mediator secreted by S. oneidensis MR-1), facilitating shuttle-mediated extracellular electron transfer. In addition, we also found that NDCN enabled enhanced contact-based direct electron transfer via outer-membrane c-type cytochromes. Taken together, the performance of MFCs with the NDCN-modified anode was enormously enhanced, delivering a maximum power density 3.5 times’ higher than that of the MFCs without the modification of carbon cloth anodes. [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 facile strategy for fabrication of conductive polyaniline (PANI) nanoflower modified carbon cloth electrode was developed and its application for microbial energy harvesting was also demonstrated. By simply tuning the concentration of aniline monomer, uniformly distributed PANI nanoflowers assembled from PANI nanoflakes anchored on the surface of carbon cloth electrode were fabricated with in-situ polymerization. Electrochemical and spectral analyses indicated that the synthesized PANI nanoflower was in conductive emeraldine salt form. Electrochemical impedance spectroscopy (EIS) analysis revealed PANI nanoflower modification reduced the charge transfer resistance of carbon cloth electrode, indicating the PANI nanoflower had excellent electrochemical activity. Furthermore, the PANI nanoflower modified electrode was used as the anode of microbial fuel cells (MFC), which delivered 2.6 and 6.5 times higher voltage and power output than these of pristine carbon cloth electrode, respectively. This work provided a controllable synthesis strategy for PANI nanostructure and demonstrated its promise in microbial energy harvesting. [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]

[Display omitted] • Shewanella loihica PV-4 exhibited high performance in reducing CO 2 to formate. • A novel three-dimensional biological self-assembled cathode was constructed. • No involvement of electron mediators was found in whole cell catalysis. • Faraday efficiency of bioelectrosynthetic CO 2 -to-formate reached 99.95%. Bioelectrochemical CO 2 reduction (bio-CO 2 R) provides a sustainable and carbon neutral power-to-chemical route. Whole-cell electrosynthesis is one of the attractive strategies to realize CO 2 R due to its simple and low-cost superiorities. However, it is still challenging to overcome the sluggish transmembrane electron transfer of microorganisms without exogenously added mediators. Here, we described the fabrication of biohydrogel that contains bio-reduced graphene oxide (rGO) and living electroactive bacteria (EAB) for bio-CO 2 R. The EAB exhibited surprising ability to self-assemble biohydrogel that was further served as biocathode to drive CO 2 -to-formate electrosynthesis. With the close interaction between EAB and rGO nanosheets, the transmembrane electron transfer achieved at high Faradaic efficiency (∼99.5 %) and 46-fold increase of formate titer without exogenous mediator. This work provided the facile and practical approach to bridge the bacterial cell and electrode for efficient electron transfer and implied the new possibility to store the electric energy into chemicals with bio-CO 2 R. [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]

The feasibility to use tartaric acid doped PANI for MFC anode modification was determined. Uniform PANI nanowires doped with tartaric acid were synthesized and formed mesoporous networks on the carbon cloth surface. By using this tartaric acid doped PANI modified carbon cloth (PANI-TA) as the anode, the voltage output (435 ± 15 mV) and power output (490 ± 12 mW/m 2 ) of MFC were enhanced by 1.6 times and 4.1 times compared to that of MFC with plain carbon cloth anode, respectively. Strikingly, the performance of PANI-TA MFC was superior to that of the MFCs with inorganic acids doped PNAI modified anode. These results substantiated that tartaric acid is a promising PANI dopant for MFC anode modification, and provided new opportunity for MFC performance improvement. [ABSTRACT FROM AUTHOR]

• Cytocompatible bacterial ATRP (b- ATRP) was developed. • Bacterial nanohybrids with high viability were obtained with b -ATRP. • The surface electric property of bacterial cells was well-controlled by b- ATRP. • Cr(VI) removal rate was improved by 3 times with bacterial nanohybrid. Surface-initiated activator regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP) has great potential to modify living cell surface with controlled architecture and tailored phenotype. However, it is challenging to engineer the bacterial cells with current SI-ARGET ATRP due to low cellular tolerance to the toxic reagents in polymerization. In this study, a cytocompatible bacterial SI-ARGET ATRP (b -ATRP) strategy was developed for individual nanoencapsulation of living bacterial cell. With step by step optimization of reaction conditions, living nanohybrid with high cell viability (>70%) was achieved with b -ATRP. Furthermore, living Shewanella nanohybrids with controllable surface electric property were fabricated with b -ATRP and applied for aqueous Cr(VI) treatment. Impressively, nanoencapsulation of cells with poly(4-vinylpyridine) improved the Cr(VI) removal rate by 3 times. This work provided a new approach to engineer the living bacterial cell surface and expanded the ATRP applications to prokaryotic cell and bioremediation. [ABSTRACT FROM AUTHOR]

• Size-controlled biosynthesis of FeS nanoparticles was achieved. • Cr(VI) removal capacity of 565.6 mg/g was achieved by FeS NP with size of 30–40 nm. • Small nanoparticle size reduced FeS passivation in Cr(VI) treatment. In this study, biogenic iron sulfide nanoparticles (FeS NPs) were synthesized by Shewanella and used for Cr(VI) removal. To control the size of FeS NPs, the biological S(-II) releasing rate was proposed as the key parameter in Fe(III) reduction and was subtly tuned with the aid of a kinetic model. Field emission scanning electron microscope (FESEM) observation revealed that gradually increased S(-II) releasing rate lead to the formation of FeS NPs with size from 30 nm to 90 nm. Impressively, the biogenic FeS NPs with 30–40 nm showed high removal rate and large removal capacity (565.6 mg/g) for removal of aqueous Cr(VI). Further analyses revealed that the improved performance of small FeS NPs was ascribed to the reduced passivation of FeS. Therefore, this study provided a facile approach for size-controlled biosynthesis of FeS NPs, and demonstrated the promise to use biogenic FeS NPs for chromate remediation. [ABSTRACT FROM AUTHOR]