Статті в журналах: "Microbial electrosynthesis systems"

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Sharma, Mohita, Yolanda Alvarez-Gallego, Wafa Achouak, Deepak Pant, Priyangshu M. Sarma, and Xochitl Dominguez-Benetton. "Electrode material properties for designing effective microbial electrosynthesis systems." Journal of Materials Chemistry A 7, no. 42 (2019): 24420–36. http://dx.doi.org/10.1039/c9ta04886c.

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(a) Pictograph and (b) schematic representation of the placement of multiple working electrodes with a single counter electrode and reference electrode using an N'Stat setup and (c) the schematic of the potentiostat interface connection with the electrochemical cell.

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Li, Xiao-Min, Long-Jun Ding, Dong Zhu, and Yong-Guan Zhu. "Long-Term Fertilization Shapes the Putative Electrotrophic Microbial Community in Paddy Soils Revealed by Microbial Electrosynthesis Systems." Environmental Science & Technology 55, no. 5 (February 18, 2021): 3430–41. http://dx.doi.org/10.1021/acs.est.0c08022.

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Kong, Fanying, Hong-Yu Ren, Spyros G. Pavlostathis, Jun Nan, Nan-Qi Ren, and Aijie Wang. "Overview of value-added products bioelectrosynthesized from waste materials in microbial electrosynthesis systems." Renewable and Sustainable Energy Reviews 125 (June 2020): 109816. http://dx.doi.org/10.1016/j.rser.2020.109816.

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Marshall, Christopher W., Daniel E. Ross, Erin B. Fichot, R. Sean Norman, and Harold D. May. "Long-term Operation of Microbial Electrosynthesis Systems Improves Acetate Production by Autotrophic Microbiomes." Environmental Science & Technology 47, no. 11 (May 16, 2013): 6023–29. http://dx.doi.org/10.1021/es400341b.

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Winder, Johanna C., Mark Hewlett, Ping Liu, and John Love. "Conversion of Biomass to Chemicals via Electrofermentation of Lactic Acid Bacteria." Energies 15, no. 22 (November 17, 2022): 8638. http://dx.doi.org/10.3390/en15228638.

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Microbial electrosynthesis is the process of supplying electrons to microorganisms to reduce CO2 and yield industrially relevant products. Such systems are limited by their requirement for high currents, resulting in challenges to cell survival. Electrofermentation is an electron-efficient form of microbial electrosynthesis in which a small cathodic or anodic current is provided to a culture to alter the oxidation–reduction potential of the medium and, in turn, alter microbial metabolism. This approach has been successfully utilised to increase yields of diverse products including biogas, butanediol and lactate. Biomass conversion to lactate is frequently facilitated by ensiling plant biomass with homofermentative lactic acid bacteria. Although most commonly used as a preservative in ensiled animal feed, lactate has diverse industrial applications as a precursor for the production of probiotics, biofuels, bioplastics and platform chemicals. Lactate yields by lactic acid bacteria (LAB) are constrained by a number of redox limitations which must be overcome while maintaining profitability and sustainability. To date, electrofermentation has not been scaled past laboratory- or pilot-stage reactions. The increasing ease of genetic modification in a wide range of LAB species may prove key to overcoming some of the pitfalls of electrofermentation at commercial scale. This review explores the history of electrofermentation as a tool for controlling redox balance within bacterial biocatalysts, and the potential for electrofermentation to increase lactate production from low-value plant biomass.

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Li, Shuwei, Young Eun Song, Jiyun Baek, Hyeon Sung Im, Mutyala Sakuntala, Minsoo Kim, Chulhwan Park, Booki Min, and Jung Rae Kim. "Bioelectrosynthetic Conversion of CO2 Using Different Redox Mediators: Electron and Carbon Balances in a Bioelectrochemical System." Energies 13, no. 10 (May 19, 2020): 2572. http://dx.doi.org/10.3390/en13102572.

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Microbial electrosynthesis (MES) systems can convert CO2 to acetate and other value-added chemicals using electricity as the reducing power. Several electrochemically active redox mediators can enhance interfacial electron transport between bacteria and the electrode in MES systems. In this study, different redox mediators, such as neutral red (NR), 2-hydroxy-1,4-naphthoquinone (HNQ), and hydroquinone (HQ), were compared to facilitate an MES-based CO2 reduction reaction on the cathode. The mediators, NR and HNQ, improved acetate production from CO2 (165 mM and 161 mM, respectively) compared to the control (without a mediator = 149 mM), whereas HQ showed lower acetate production (115 mM). On the other hand, when mediators were used, the electron and carbon recovery efficiency decreased because of the presence of bioelectrochemical reduction pathways other than acetate production. Cyclic voltammetry of an MES with such mediators revealed CO2 reduction to acetate on the cathode surface. These results suggest that the addition of mediators to MES can improve CO2 conversion to acetate with further optimization in an operating strategy of electrosynthesis processes.

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Izadi, Paniz, Jean-Marie Fontmorin, Swee Su Lim, Ian M. Head, and Eileen H. Yu. "Enhanced bio-production from CO2 by microbial electrosynthesis (MES) with continuous operational mode." Faraday Discussions 230 (2021): 344–59. http://dx.doi.org/10.1039/d0fd00132e.

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Continuous operational mode increased systems efficiency compared to fed-batch mode. Hydraulic retention time (HRT) affected the production pattern. Short and long HRT increased acetate production rate and products diversity, respectively.

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Hou, Xia, Liping Huang, Peng Zhou, Fuping Tian, Ye Tao, and Gianluca Li Puma. "Electrosynthesis of acetate from inorganic carbon (HCO3−) with simultaneous hydrogen production and Cd(II) removal in multifunctional microbial electrosynthesis systems (MES)." Journal of Hazardous Materials 371 (June 2019): 463–73. http://dx.doi.org/10.1016/j.jhazmat.2019.03.028.

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Li, Zhuo, Qian Fu, Hao Chen, Shuai Xiao, Jun Li, Qiang Liao, and Xun Zhu. "A mathematical model for CO2 conversion of CH4-producing biocathodes in microbial electrosynthesis systems." Renewable Energy 183 (January 2022): 719–28. http://dx.doi.org/10.1016/j.renene.2021.11.050.

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Li, Zhuo, Qian Fu, Hajime Kobayashi, Shuai Xiao, Jun Li, Liang Zhang, Qiang Liao, and Xun Zhu. "Polarity reversal facilitates the development of biocathodes in microbial electrosynthesis systems for biogas production." International Journal of Hydrogen Energy 44, no. 48 (October 2019): 26226–36. http://dx.doi.org/10.1016/j.ijhydene.2019.08.117.

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Anwer, Abdul, Nishat Khan, Mohammad Umar, Mohd Rafatullah, and Mohammad Khan. "Electrodeposited Hybrid Biocathode-Based CO2 Reduction via Microbial Electro-Catalysis to Biofuels." Membranes 11, no. 3 (March 22, 2021): 223. http://dx.doi.org/10.3390/membranes11030223.

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Microbial electrosynthesis is a new approach to converting C1 carbon (CO2) to more complex carbon-based products. In the present study, CO2, a potential greenhouse gas, was used as a sole carbon source and reduced to value-added chemicals (acetate, ethanol) with the help of bioelectrochemical reduction in microbial electrosynthesis systems (MES). The performance of MES was studied with varying electrode materials (carbon felt, stainless steel, and cobalt electrodeposited carbon felt). The MES performance was assessed in terms of acetic acid and ethanol production with the help of gas chromatography (GC). The electrochemical characterization of the system was analyzed with chronoamperometry and cyclic voltammetry. The study revealed that the MES operated with hybrid cobalt electrodeposited carbon felt electrode yielded the highest acetic acid (4.4 g/L) concentration followed by carbon felt/stainless steel (3.7 g/L), plain carbon felt (2.2 g/L), and stainless steel (1.87 g/L). The alcohol concentration was also observed to be highest for the hybrid electrode (carbon felt/stainless steel/cobalt oxide is 0.352 g/L) as compared to the bare electrodes (carbon felt is 0.22 g/L) tested, which was found to be in correspondence with the pH changes in the system. Electrochemical analysis revealed improved electrotrophy in the hybrid electrode, as confirmed by the increased redox current for the hybrid electrode as compared to plain electrodes. Cyclic voltammetry analysis also confirmed the role of the biocatalyst developed on the electrode in CO2 sequestration.

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Mateos, Raúl, Ana Sotres, Raúl M. Alonso, Antonio Morán, and Adrián Escapa. "Enhanced CO2 Conversion to Acetate through Microbial Electrosynthesis (MES) by Continuous Headspace Gas Recirculation." Energies 12, no. 17 (August 27, 2019): 3297. http://dx.doi.org/10.3390/en12173297.

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Bioelectrochemical systems (BESs) is a term that encompasses a group of novel technologies able to interconvert electrical energy and chemical energy by means of a bioelectroactive biofilm. Microbial electrosynthesis (MES) systems, which branch off from BESs, are able to convert CO2 into valuable organic chemicals and fuels. This study demonstrates that CO2 reduction in MES systems can be enhanced by enriching the inoculum and improving CO2 availability to the biofilm. The proposed system is proven to be a repetitive, efficient, and selective way of consuming CO2 for the production of acetic acid, showing cathodic efficiencies of over 55% and CO2 conversions of over 80%. Continuous recirculation of the gas headspace through the catholyte allowed for a 44% improvement in performance, achieving CO2 fixation rates of 171 mL CO2 L−1·d−1, a maximum daily acetate production rate of 261 mg HAc·L−1·d−1, and a maximum acetate titer of 1957 mg·L−1. High-throughput sequencing revealed that CO2 reduction was mainly driven by a mixed-culture biocathode, in which Sporomusa and Clostridium, both bioelectrochemical acetogenic bacteria, were identified together with other species such as Desulfovibrio, Pseudomonas, Arcobacter, Acinetobacter or Sulfurospirillum, which are usually found in cathodic biofilms. Moreover, results suggest that these communities are responsible of maintaining a stable reactor performance.

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13

Tahir, Khurram, Abdul Samee Ali, Bolam Kim, Youngsu Lim, and Dae Sung Lee. "Spent Tea Leaves and Coffee Grounds as Potential Biocathode for Improved Microbial Electrosynthesis Performance." International Journal of Energy Research 2023 (February 24, 2023): 1–9. http://dx.doi.org/10.1155/2023/1318365.

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Microbial electrosynthesis (MES) has emerged as a sustainable energy platform capable of simultaneous wastewater treatment and valuable chemical production. The performance of MES, like other bioelectrochemical systems, largely depends on its electrode (cathode), providing the platform for microbial growth as well as electron transfer. However, most of the electrodes are expensive, and their nonrenewable characteristics, cost, and poisoning nature are major bottlenecks in MES commercialization. Thus, several efforts have been made to explore the potential of waste carbon-based electrodes to reduce carbon footprints as well as electrode manufacturing costs. In this study, the feasibility of using spent tea leaves (STL) and spent coffee grounds (SCG) as MES biocathode was tested. Different bioelectrochemical tests suggested improved MES performance with STL and SCG biocathode along with reduced electrode resistance and improved current density. A 1.5- and 2.0-fold increase in cyclic voltammetry (CV) current output was observed for SCG and STL, respectively, with substantial mediator peaks of high intensity indicating enhanced electrocatalytic activity. Enrichment of some fermentative and exoelectrogenic microbial classes such as Clostridia, Bacteroidia, and Deltaproteobacteria led to a 1.3- and 1.4-fold increase in butyrate production for SCG and STL cathode, respectively. These results demonstrate the potential of STL and SCG as MES cathode for improved energy and chemical production.

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Leger, Dorian, Silvio Matassa, Elad Noor, Alon Shepon, Ron Milo, and Arren Bar-Even. "Photovoltaic-driven microbial protein production can use land and sunlight more efficiently than conventional crops." Proceedings of the National Academy of Sciences 118, no. 26 (June 21, 2021): e2015025118. http://dx.doi.org/10.1073/pnas.2015025118.

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Population growth and changes in dietary patterns place an ever-growing pressure on the environment. Feeding the world within sustainable boundaries therefore requires revolutionizing the way we harness natural resources. Microbial biomass can be cultivated to yield protein-rich feed and food supplements, collectively termed single-cell protein (SCP). Yet, we still lack a quantitative comparison between traditional agriculture and photovoltaic-driven SCP systems in terms of land use and energetic efficiency. Here, we analyze the energetic efficiency of harnessing solar energy to produce SCP from air and water. Our model includes photovoltaic electricity generation, direct air capture of carbon dioxide, electrosynthesis of an electron donor and/or carbon source for microbial growth (hydrogen, formate, or methanol), microbial cultivation, and the processing of biomass and proteins. We show that, per unit of land, SCP production can reach an over 10-fold higher protein yield and at least twice the caloric yield compared with any staple crop. Altogether, this quantitative analysis offers an assessment of the future potential of photovoltaic-driven microbial foods to supplement conventional agricultural production and support resource-efficient protein supply on a global scale.

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Chandrasekhar, K., A. Naresh Kumar, Tirath Raj, Gopalakrishnan Kumar, and Sang-Hyoun Kim. "Bioelectrochemical system-mediated waste valorization." Systems Microbiology and Biomanufacturing 1, no. 4 (July 9, 2021): 432–43. http://dx.doi.org/10.1007/s43393-021-00039-7.

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AbstractBioelectrochemical systems (BESs) are a new and emerging technology in the field of fermentation technology. Electrical energy was provided externally to the microbial electrolysis cells (MECs) to generate hydrogen or value-added chemicals, including caustic, formic acid, acetic acid, and peroxide. Also, BES was designed to recover nutrients, metals or remove recalcitrant compounds. The variety of naturally existing microorganisms and enzymes act as a biocatalyst to induce potential differences amid the electrodes. BESs can be performed with non-catalyzed electrodes (both anode and cathode) under favorable circumstances, unlike conventional fuel cells. In recent years, value-added chemical producing microbial electrosynthesis (MES) technology has intensely broadened the prospect for BES. An additional strategy includes the introduction of innovative technologies that help with the manufacturing of alternative materials for electrode preparation, ion-exchange membranes, and pioneering designs. Because of this, BES is emerging as a promising technology. This article deliberates recent signs of progress in BESs so far, focusing on their diverse applications beyond electricity generation and resulting performance.

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Huang, Liping, Zijing Xu, Yinghong Shi, Yu Zhang, and Gianluca Li Puma. "Cellular electron transfer in anaerobic photo-assisted biocathode microbial electrosynthesis systems for acetate production from inorganic carbon (HCO3–)." Chemical Engineering Journal 431 (March 2022): 134022. http://dx.doi.org/10.1016/j.cej.2021.134022.

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Tharak, Athmakuri, and S. Venkata Mohan. "Syngas Fermentation to Acetate and Ethanol with Adaptative Electroactive Carboxydotrophs in Single Chambered Microbial Electrochemical System." Micromachines 13, no. 7 (June 21, 2022): 980. http://dx.doi.org/10.3390/mi13070980.

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Microbial electrosynthesis system (MES; single-chambered) was fabricated and evaluated with carbon cloth/graphite as a working/counter electrode employing an enriched microbiome. Continuous syngas sparging (at working electrode; WE) enabled the growth of endo electrogenic bacteria by availing the inorganic carbon source. Applied potential (−0.5 V) on the working electrode facilitated the reduction in syngas, leading to the synthesis of fatty acids and alcohols. The higher acetic acid titer of 3.8 g/L and ethanol concentration of 0.2 g/L was observed at an active microbial metabolic state, evidencing the shift in metabolism from acetogenic to solventogenesis. Voltammograms evidenced distinct redox species with low charge transfer resistance (Rct; Nyquist impedance). Reductive catalytic current (−0.02 mA) enabled the charge transfer efficiency of the cathodes favoring syngas conversion to products. The surface morphology of carbon cloth and system-designed conditions favored the growth of electrochemically active consortia. Metagenomic analysis revealed the enrichment of phylum/class with Actinobacteria, Firmicutes/Clostridia and Bacilli, which accounts for the syngas fermentation through suitable gene loci.

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Hou, Xia, and Liping Huang. "Synergetic magnetic field and loaded Fe3O4 for simultaneous efficient acetate production and Cr(VI) removal in microbial electrosynthesis systems." Chemical Engineering Journal Advances 2 (October 2020): 100019. http://dx.doi.org/10.1016/j.ceja.2020.100019.

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Tahir, Khurram, Nagesh Maile, Ahsan Abdul Ghani, Bolam Kim, Jiseon Jang, and Dae Sung Lee. "Development of a three-dimensional macroporous sponge biocathode coated with carbon nanotube–MXene composite for high-performance microbial electrosynthesis systems." Bioelectrochemistry 146 (August 2022): 108140. http://dx.doi.org/10.1016/j.bioelechem.2022.108140.

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Kong, Weifeng, Liping Huang, Xie Quan, Zongbin Zhao, and Gianluca Li Puma. "Efficient production of acetate from inorganic carbon (HCO3–) in microbial electrosynthesis systems incorporating Ag3PO4/g-C3N4 anaerobic photo-assisted biocathodes." Applied Catalysis B: Environmental 284 (May 2021): 119696. http://dx.doi.org/10.1016/j.apcatb.2020.119696.

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Strycharz-Glaven, Sarah M., Richard H. Glaven, Zheng Wang, Jing Zhou, Gary J. Vora, and Leonard M. Tender. "Electrochemical Investigation of a Microbial Solar Cell Reveals a Nonphotosynthetic Biocathode Catalyst." Applied and Environmental Microbiology 79, no. 13 (April 19, 2013): 3933–42. http://dx.doi.org/10.1128/aem.00431-13.

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ABSTRACTMicrobial solar cells (MSCs) are microbial fuel cells (MFCs) that generate their own oxidant and/or fuel through photosynthetic reactions. Here, we present electrochemical analyses and biofilm 16S rRNA gene profiling of biocathodes of sediment/seawater-based MSCs inoculated from the biocathode of a previously described sediment/seawater-based MSC. Electrochemical analyses indicate that for these second-generation MSC biocathodes, catalytic activity diminishes over time if illumination is provided during growth, whereas it remains relatively stable if growth occurs in the dark. For both illuminated and dark MSC biocathodes, cyclic voltammetry reveals a catalytic-current–potential dependency consistent with heterogeneous electron transfer mediated by an insoluble microbial redox cofactor, which was conserved following enrichment of the dark MSC biocathode using a three-electrode configuration. 16S rRNA gene profiling showedGammaproteobacteria, most closely related toMarinobacterspp., predominated in the enriched biocathode. The enriched biocathode biofilm is easily cultured on graphite cathodes, forms a multimicrobe-thick biofilm (up to 8.2 μm), and does not lose catalytic activity after exchanges of the reactor medium. Moreover, the consortium can be grown on cathodes with only inorganic carbon provided as the carbon source, which may be exploited for proposed bioelectrochemical systems for electrosynthesis of organic carbon from carbon dioxide. These results support a scheme where two distinct communities of organisms develop within MSC biocathodes: one that is photosynthetically active and one that catalyzes reduction of O2by the cathode, where the former partially inhibits the latter. The relationship between the two communities must be further explored to fully realize the potential for MSC applications.

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Krige, Adolf, Magnus Sjöblom, Kerstin Ramser, Paul Christakopoulos, and Ulrika Rova. "On-Line Raman Spectroscopic Study of Cytochromes’ Redox State of Biofilms in Microbial Fuel Cells." Molecules 24, no. 3 (February 12, 2019): 646. http://dx.doi.org/10.3390/molecules24030646.

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Bio-electrochemical systems such as microbial fuel cells and microbial electrosynthesis cells depend on efficient electron transfer between the microorganisms and the electrodes. Understanding the mechanisms and dynamics of the electron transfer is important in order to design more efficient reactors, as well as modifying microorganisms for enhanced electricity production. Geobacter are well known for their ability to form thick biofilms and transfer electrons to the surfaces of electrodes. Currently, there are not many “on-line” systems for monitoring the activity of the biofilm and the electron transfer process without harming the biofilm. Raman microscopy was shown to be capable of providing biochemical information, i.e., the redox state of C-type cytochromes, which is integral to external electron transfer, without harming the biofilm. In the current study, a custom 3D printed flow-through cuvette was used in order to analyze the oxidation state of the C-type cytochromes of suspended cultures of three Geobacter sulfurreducens strains (PCA, KN400 and ΔpilA). It was found that the oxidation state is a good indicator of the metabolic state of the cells. Furthermore, an anaerobic fluidic system enabling in situ Raman measurements was designed and applied successfully to monitor and characterize G. sulfurreducens biofilms during electricity generation, for both a wild strain, PCA, and a mutant, ΔS. The cytochrome redox state, monitored by the Raman peak areas, could be modulated by applying different poise voltages to the electrodes. This also correlated with the modulation of current transferred from the cytochromes to the electrode. The Raman peak area changed in a predictable and reversible manner, indicating that the system could be used for analyzing the oxidation state of the proteins responsible for the electron transfer process and the kinetics thereof in-situ.

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Qian, Yitong, Liping Huang, Peng Zhou, Fuping Tian, and Gianluca Li Puma. "Reduction of Cu(II) and simultaneous production of acetate from inorganic carbon by Serratia Marcescens biofilms and plankton cells in microbial electrosynthesis systems." Science of The Total Environment 666 (May 2019): 114–25. http://dx.doi.org/10.1016/j.scitotenv.2019.02.267.

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Cai, Zhenghong, Liping Huang, Xie Quan, Zongbin Zhao, Yong Shi, and Gianluca Li Puma. "Acetate production from inorganic carbon (HCO3-) in photo-assisted biocathode microbial electrosynthesis systems using WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens species." Applied Catalysis B: Environmental 267 (June 2020): 118611. http://dx.doi.org/10.1016/j.apcatb.2020.118611.

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Morrison, Clifford S., Elena E. Paskaleva, Marvin A. Rios, Thomas R. Beusse, Elaina M. Blair, Lucy Q. Lin, James R. Hu, et al. "Improved soluble expression and use of recombinant human renalase." PLOS ONE 15, no. 11 (November 12, 2020): e0242109. http://dx.doi.org/10.1371/journal.pone.0242109.

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Electrochemical bioreactor systems have enjoyed significant attention in the past few decades, particularly because of their applications to biobatteries, artificial photosynthetic systems, and microbial electrosynthesis. A key opportunity with electrochemical bioreactors is the ability to employ cofactor regeneration strategies critical in oxidative and reductive enzymatic and cell-based biotransformations. Electrochemical cofactor regeneration presents several advantages over other current cofactor regeneration systems, such as chemoenzymatic multi-enzyme reactions, because there is no need for a sacrificial substrate and a recycling enzyme. Additionally, process monitoring is simpler and downstream processing is less costly. However, the direct electrochemical reduction of NAD(P)+ on a cathode may produce adventitious side products, including isomers of NAD(P)H that can act as potent competitive inhibitors to NAD(P)H-requiring enzymes such as dehydrogenases. To overcome this limitation, we examined how nature addresses the adventitious formation of isomers of NAD(P)H. Specifically, renalases are enzymes that catalyze the oxidation of 1,2- and 1,6-NAD(P)H to NAD(P)+, yielding an effective recycling of unproductive NAD(P)H isomers. We designed several mutants of recombinant human renalase isoform 1 (rhRen1), expressed them in E. coli BL21(DE3) to enhance protein solubility, and evaluated the activity profiles of the renalase variants against NAD(P)H isomers. The potential for rhRen1 to be employed in engineering applications was then assessed in view of the enzyme’s stability upon immobilization. Finally, comparative modeling was performed to assess the underlying reasons for the enhanced solubility and activity of the mutant enzymes.

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Lust, Rauno, Jaak Nerut, Kuno Kasak, and Ülo Mander. "Enhancing Nitrate Removal from Waters with Low Organic Carbon Concentration Using a Bioelectrochemical System—A Pilot-Scale Study." Water 12, no. 2 (February 13, 2020): 516. http://dx.doi.org/10.3390/w12020516.

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Assessments of groundwater aquifers made around the world show that in many cases, nitrate concentrations exceed the safe drinking water threshold. This study assessed how bioelectrochemical systems could be used to enhance nitrate removal from waters with low organic carbon concentrations. A two-chamber microbial electrosynthesis cell (MES) was constructed and operated for 45 days with inoculum that was taken from a municipal wastewater treatment plant. A study showed that MES can be used to enhance nitrate removal efficiency from 3.66% day−1 in a control reactor to 8.54% day−1 in the MES reactor, if a cathode is able to act as an electron donor for autotrophic denitrifying bacteria or there is reducing oxygen in a cathodic chamber to favor denitrification. In the MES, greenhouse gas emissions were also lower compared to the control. Nitrous oxide average fluxes were −639.59 and −9.15 µg N m−2 h−1 for the MES and control, respectively, and the average carbon dioxide fluxes were −5.28 and 43.80 mg C m−2 h−1, respectively. The current density correlated significantly with the dissolved oxygen concentration, indicating that it is essential to keep the dissolved oxygen concentration in the cathode chamber as low as possible, not only to suppress oxygen’s inhibiting effect on denitrification but also to achieve better power efficiency.

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Sadhukhan, Jhuma, Jon R. Lloyd, Keith Scott, Giuliano C. Premier, Eileen H. Yu, Tom Curtis, and Ian M. Head. "A critical review of integration analysis of microbial electrosynthesis (MES) systems with waste biorefineries for the production of biofuel and chemical from reuse of CO 2." Renewable and Sustainable Energy Reviews 56 (April 2016): 116–32. http://dx.doi.org/10.1016/j.rser.2015.11.015.

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Hou, Jiaxin, Liping Huang, Peng Zhou, Yitong Qian, and Ning Li. "Understanding the interdependence of strain of electrotroph, cathode potential and initial Cu(II) concentration for simultaneous Cu(II) removal and acetate production in microbial electrosynthesis systems." Chemosphere 243 (March 2020): 125317. http://dx.doi.org/10.1016/j.chemosphere.2019.125317.

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Breuer, Marian, Kevin M. Rosso, Jochen Blumberger, and Julea N. Butt. "Multi-haem cytochromes in Shewanella oneidensis MR-1: structures, functions and opportunities." Journal of The Royal Society Interface 12, no. 102 (January 2015): 20141117. http://dx.doi.org/10.1098/rsif.2014.1117.

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Multi-haem cytochromes are employed by a range of microorganisms to transport electrons over distances of up to tens of nanometres. Perhaps the most spectacular utilization of these proteins is in the reduction of extracellular solid substrates, including electrodes and insoluble mineral oxides of Fe(III) and Mn(III/IV), by species of Shewanella and Geobacter. However, multi-haem cytochromes are found in numerous and phylogenetically diverse prokaryotes where they participate in electron transfer and redox catalysis that contributes to biogeochemical cycling of N, S and Fe on the global scale. These properties of multi-haem cytochromes have attracted much interest and contributed to advances in bioenergy applications and bioremediation of contaminated soils. Looking forward, there are opportunities to engage multi-haem cytochromes for biological photovoltaic cells, microbial electrosynthesis and developing bespoke molecular devices. As a consequence, it is timely to review our present understanding of these proteins and we do this here with a focus on the multitude of functionally diverse multi-haem cytochromes in Shewanella oneidensis MR-1. We draw on findings from experimental and computational approaches which ideally complement each other in the study of these systems: computational methods can interpret experimentally determined properties in terms of molecular structure to cast light on the relation between structure and function. We show how this synergy has contributed to our understanding of multi-haem cytochromes and can be expected to continue to do so for greater insight into natural processes and their informed exploitation in biotechnologies.

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Shumyantseva, V. V., T. V. Bulko, E. V. Suprun, A. V. Kuzikov, L. E. Agafonova, and A. I. Archakov. "Electrochemical methods for biomedical investigations." Biomeditsinskaya Khimiya 61, no. 2 (2015): 188–202. http://dx.doi.org/10.18097/pbmc20156102188.

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In the review, authors discussed recently published experimental data concerning highly sensitive electrochemical methods and technologies for biomedical investigations in the postgenomic era. Developments in electrochemical biosensors systems for the analysis of various bio objects are also considered: cytochrome P450s, cardiac markers, bacterial cells, the analysis of proteins based on electro oxidized amino acids as a tool for analysis of conformational events. The electroanalysis of catalytic activity of cytochromes P450 allowed developing system for screening of potential substrates, inhibitors or modulators of catalytic functions of this class of hemoproteins. The highly sensitive quartz crystal microbalance (QCM) immunosensor has been developed for analysis of bio affinity interactions of antibodies with troponin I in plasma. The QCM technique allowed real-time monitoring of the kinetic differences in specific interactions and nonspecific sorption, without multiple labeling procedures and separation steps. The affinity binding process was characterized by the association (ka) and the dissociation (kd) kinetic constants and the equilibrium association (K) constant, calculated using experimental data. Based on the electroactivity of bacterial cells, the electrochemical system for determination of sensitivity of the microbial cells to antibiotics cefepime, ampicillin, amikacin, and erythromycin was proposed. It was shown that the minimally detectable cell number corresponds to 106 CFU per electrode. The electrochemical method allows estimating the degree of E.coli JM109 cells resistance to antibiotics within 2-5 h. Electrosynthesis of polymeric analogs of antibodies for myoglobin (molecularly imprinted polymer, MIP) on the surface of graphite screen-printed electrodes as sensor elements with o- phenylenediamine as the functional monomer was developed. Molecularly imprinted polymers demonstrate selective complementary binding of a template protein molecule (myoglobin) by the "key - lock" principle.

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Huang, Liping, Shiping Song, Zhenghong Cai, Peng Zhou, and Gianluca Li Puma. "Efficient conversion of bicarbonate (HCO3−) to acetate and simultaneous heavy metal Cr(VI) removal in photo-assisted microbial electrosynthesis systems combining WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens electrotroph." Chemical Engineering Journal 406 (February 2021): 126786. http://dx.doi.org/10.1016/j.cej.2020.126786.

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32

Savcheniuk, M., B. Yarchuk, L. Korniienko, T. Tsarenko, D. Okhrimenko, I. Yanchevskyi, O. Dovhal, S. Bilyk, P. Shulha та O. Novik. "Use of ozone for dіcrease of microbal load". Naukovij vìsnik veterinarnoï medicini, № 2(160) (24 листопада 2020): 50–55. http://dx.doi.org/10.33245/2310-4902-2020-160-2-50-55.

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Ozone enters into chemical reaction with many organic compounds. Ozone is a very strong oxidant. It oxidizes most of the elements to higher oxides. In the oxidation reaction by ozone activity second only to ﬂuorine, its oxide and free radicals. It is formed from oxygen by absorbing heat in this case, and, conversely, when the expansion goes into oxygen, giving oﬀ heat. The main method of obtaining ozone for practical purposes is electrosynthesis. In industrial conditions for using ozone and corona discharge barrier. Ozonizers corona discharge can signiﬁcantly increase the eﬃciency of ozone by reducing capital and operating costs for the process equipment and ozonation. Research shows that ozone air ozonator pulsed mode increases the resistance of animals to the action of microorganisms factor. In animals and poultry in industrial production often develop diseases caused by pathogens factor. These diseases mainly occurring symptom of lesions of the respiratory and digestive systems. In many countries today conducted research using ozone, and the results of these studies are published in the course of scientiﬁc-metric database. For normal growing animals, especially young animals, premises should be thoroughly disinfected. Disinfection is required for all technological facilities as livestock and poultry. Experimentally found that ozone has a bactericidal eﬀect (for example, test cultures E. coli) on diﬀerent surfaces (wood, Petri dish) considering its concentration and exposure. The results of inﬂuence of diﬀerent concentrations of ozone in ozonair mixture is fed into the container of the Petri dish, and time impact on survival of microorganisms provides a fairly accurate prediction of the results of impact parameters ozonation. Key words: ozon, ozone therapy, Escherichia coli, disinfection.

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33

Deutzmann, Jörg S., Merve Sahin, and Alfred M. Spormann. "Extracellular Enzymes Facilitate Electron Uptake in Biocorrosion and Bioelectrosynthesis." mBio 6, no. 2 (April 21, 2015). http://dx.doi.org/10.1128/mbio.00496-15.

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ABSTRACTDirect, mediator-free transfer of electrons between a microbial cell and a solid phase in its surrounding environment has been suggested to be a widespread and ecologically significant process. The high rates of microbial electron uptake observed during microbially influenced corrosion of iron [Fe(0)] and during microbial electrosynthesis have been considered support for a direct electron uptake in these microbial processes. However, the underlying molecular mechanisms of direct electron uptake are unknown. We investigated the electron uptake characteristics of the Fe(0)-corroding and electromethanogenic archaeonMethanococcus maripaludisand discovered that free, surface-associated redox enzymes, such as hydrogenases and presumably formate dehydrogenases, are sufficient to mediate an apparent direct electron uptake. In genetic and biochemical experiments, we showed that these enzymes, which are released from cells during routine culturing, catalyze the formation of H2or formate when sorbed to an appropriate redox-active surface. These low-molecular-weight products are rapidly consumed byM. maripaludiscells when present, thereby preventing their accumulation to any appreciable or even detectable level. Rates of H2and formate formation by cell-free spent culture medium were sufficient to explain the observed rates of methane formation from Fe(0) and cathode-derived electrons by wild-typeM. maripaludisas well as by a mutant strain carrying deletions in all catabolic hydrogenases. Our data collectively show that cell-derived free enzymes can mimic direct extracellular electron transfer during Fe(0) corrosion and microbial electrosynthesis and may represent an ecologically important but so far overlooked mechanism in biological electron transfer.IMPORTANCEThe intriguing trait of some microbial organisms to engage in direct electron transfer is thought to be widespread in nature. Consequently, direct uptake of electrons into microbial cells from solid surfaces is assumed to have a significant impact not only on fundamental microbial and biogeochemical processes but also on applied bioelectrochemical systems, such as microbial electrosynthesis and biocorrosion. This study provides a simple mechanistic explanation for frequently observed fast electron uptake kinetics in microbiological systems without a direct transfer: free, cell-derived enzymes can interact with cathodic surfaces and catalyze the formation of intermediates that are rapidly consumed by microbial cells. This electron transfer mechanism likely plays a significant role in various microbial electron transfer reactions in the environment.

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Liang, Qinjun, Yu Gao, Zhigang Li, Jiayi Cai, Na Chu, Wen Hao, Yong Jiang, and Raymond Jianxiong Zeng. "Electricity-driven ammonia oxidation and acetate production in microbial electrosynthesis systems." Frontiers of Environmental Science & Engineering 16, no. 4 (July 15, 2021). http://dx.doi.org/10.1007/s11783-021-1476-5.

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Ragab, Ala’a, Dario R. Shaw, Krishna P. Katuri, and Pascal E. Saikaly. "Draft Genome Sequence of Methanobacterium sp. Strain 34x, Reconstructed from an Enriched Electromethanogenic Biocathode." Microbiology Resource Announcements 8, no. 45 (November 7, 2019). http://dx.doi.org/10.1128/mra.01138-19.

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A draft genome sequence of Methanobacterium sp. strain 34x was reconstructed from the metagenome of an enriched electromethanogenic biocathode operated in a microbial electrosynthesis (MES) reactor. Methanobacterium sp. strain 34x has 68.98% nucleotide-level genomic similarity with the closest related methanogen available with a whole-genome assembly, Methanobacterium lacus strain AL-21. This genome will provide insight into the functional potential of methanogens at the biocathodes of MES systems.

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Cabau-Peinado, Oriol, Adrie J. J. Straathof, and Ludovic Jourdin. "A General Model for Biofilm-Driven Microbial Electrosynthesis of Carboxylates From CO2." Frontiers in Microbiology 12 (June 4, 2021). http://dx.doi.org/10.3389/fmicb.2021.669218.

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Up to now, computational modeling of microbial electrosynthesis (MES) has been underexplored, but is necessary to achieve breakthrough understanding of the process-limiting steps. Here, a general framework for modeling microbial kinetics in a MES reactor is presented. A thermodynamic approach is used to link microbial metabolism to the electrochemical reduction of an intracellular mediator, allowing to predict cellular growth and current consumption. The model accounts for CO2 reduction to acetate, and further elongation to n-butyrate and n-caproate. Simulation results were compared with experimental data obtained from different sources and proved the model is able to successfully describe microbial kinetics (growth, chain elongation, and product inhibition) and reactor performance (current density, organics titer). The capacity of the model to simulate different system configurations is also shown. Model results suggest CO2 dissolved concentration might be limiting existing MES systems, and highlight the importance of the delivery method utilized to supply it. Simulation results also indicate that for biofilm-driven reactors, continuous mode significantly enhances microbial growth and might allow denser biofilms to be formed and higher current densities to be achieved.

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Abdollahi, Maliheh, Sara Al Sbei, Miriam A. Rosenbaum, and Falk Harnisch. "The oxygen dilemma: The challenge of the anode reaction for microbial electrosynthesis from CO2." Frontiers in Microbiology 13 (August 3, 2022). http://dx.doi.org/10.3389/fmicb.2022.947550.

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Microbial electrosynthesis (MES) from CO2 provides chemicals and fuels by driving the metabolism of microorganisms with electrons from cathodes in bioelectrochemical systems. These microorganisms are usually strictly anaerobic. At the same time, the anode reaction of bioelectrochemical systems is almost exclusively water splitting through the oxygen evolution reaction (OER). This creates a dilemma for MES development and engineering. Oxygen penetration to the cathode has to be excluded to avoid toxicity and efficiency losses while assuring low resistance. We show that this dilemma derives a strong need to identify novel reactor designs when using the OER as an anode reaction or to fully replace OER with alternative oxidation reactions.

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38

Mills, Simon, Paolo Dessì, Deepak Pant, Pau Farràs, William T. Sloan, Gavin Collins, and Umer Zeeshan Ijaz. "A meta-analysis of acetogenic and methanogenic microbiomes in microbial electrosynthesis." npj Biofilms and Microbiomes 8, no. 1 (September 23, 2022). http://dx.doi.org/10.1038/s41522-022-00337-5.

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AbstractA meta-analysis approach was used, to study the microbiomes of biofilms and planktonic communities underpinning microbial electrosynthesis (MES) cells. High-throughput DNA sequencing of 16S rRNA gene amplicons has been increasingly applied to understand MES systems. In this meta-analysis of 22 studies, we find that acetogenic and methanogenic MES cells share 80% of a cathodic core microbiome, and that different inoculum pre-treatments strongly affect community composition. Oxygen scavengers were more abundant in planktonic communities, and several key organisms were associated with operating parameters and good cell performance. We suggest Desulfovibrio sp. play a role in initiating early biofilm development and shaping microbial communities by catalysing H2 production, to sustain either Acetobacterium sp. or Methanobacterium sp. Microbial community assembly became more stochastic over time, causing diversification of the biofilm (cathodic) community in acetogenic cells and leading to re-establishment of methanogens, despite inoculum pre-treatments. This suggests that repeated interventions may be required to suppress methanogenesis.

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Eddie, Brian J., Zheng Wang, W. Judson Hervey, Dagmar H. Leary, Anthony P. Malanoski, Leonard M. Tender, Baochuan Lin, and Sarah M. Strycharz-Glaven. "Metatranscriptomics Supports the Mechanism for Biocathode Electroautotrophy by “Candidatus Tenderia electrophaga”." mSystems 2, no. 2 (March 28, 2017). http://dx.doi.org/10.1128/msystems.00002-17.

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ABSTRACT Bacteria that directly use electrodes as metabolic electron donors (biocathodes) have been proposed for applications ranging from microbial electrosynthesis to advanced bioelectronics for cellular communication with machines. However, just as we understand very little about oxidation of analogous natural insoluble electron donors, such as iron oxide, the organisms and extracellular electron transfer (EET) pathways underlying the electrode-cell direct electron transfer processes are almost completely unknown. Biocathodes are a stable biofilm cultivation platform to interrogate both the rate and mechanism of EET using electrochemistry and to study the electroautotrophic organisms that catalyze these reactions. Here we provide new evidence supporting the hypothesis that the uncultured bacterium “Candidatus Tenderia electrophaga” directly couples extracellular electron transfer to CO2 fixation. Our results provide insight into developing biocathode technology, such as microbial electrosynthesis, as well as advancing our understanding of chemolithoautotrophy. Biocathodes provide a stable electron source to drive reduction reactions in electrotrophic microbial electrochemical systems. Electroautotrophic biocathode communities may be more robust than monocultures in environmentally relevant settings, but some members are not easily cultivated outside the electrode environment. We previously used metagenomics and metaproteomics to propose a pathway for coupling extracellular electron transfer (EET) to carbon fixation in “Candidatus Tenderia electrophaga,” an uncultivated but dominant member of an electroautotrophic biocathode community. Here we validate and refine this proposed pathway using metatranscriptomics of replicate aerobic biocathodes poised at the growth potential level of 310 mV and the suboptimal 470 mV (versus the standard hydrogen electrode). At both potentials, transcripts were more abundant from “Ca. Tenderia electrophaga” than from any other constituent, and its relative activity was positively correlated with current. Several genes encoding key components of the proposed “Ca. Tenderia electrophaga” EET pathway were more highly expressed at 470 mV, consistent with a need for cells to acquire more electrons to obtain the same amount of energy as at 310 mV. These included cyc2, encoding a homolog of a protein known to be involved in iron oxidation. Mean expression of all CO2 fixation-related genes is 0.27 log2-fold higher at 310 mV, indicating that reduced energy availability at 470 mV decreased CO2 fixation. Our results substantiate the claim that “Ca. Tenderia electrophaga” is the key electroautotroph, which will help guide further development of this community for microbial electrosynthesis. IMPORTANCE Bacteria that directly use electrodes as metabolic electron donors (biocathodes) have been proposed for applications ranging from microbial electrosynthesis to advanced bioelectronics for cellular communication with machines. However, just as we understand very little about oxidation of analogous natural insoluble electron donors, such as iron oxide, the organisms and extracellular electron transfer (EET) pathways underlying the electrode-cell direct electron transfer processes are almost completely unknown. Biocathodes are a stable biofilm cultivation platform to interrogate both the rate and mechanism of EET using electrochemistry and to study the electroautotrophic organisms that catalyze these reactions. Here we provide new evidence supporting the hypothesis that the uncultured bacterium “Candidatus Tenderia electrophaga” directly couples extracellular electron transfer to CO2 fixation. Our results provide insight into developing biocathode technology, such as microbial electrosynthesis, as well as advancing our understanding of chemolithoautotrophy.

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Bajracharya, Suman, Adolf Krige, Leonidas Matsakas, Ulrika Rova, and Paul Christakopoulos. "Advances in cathode designs and reactor configurations of microbial electrosynthesis systems to facilitate gas electro-fermentation." Bioresource Technology, April 2022, 127178. http://dx.doi.org/10.1016/j.biortech.2022.127178.

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Kong, Weifeng, Liping Huang, Xie Quan, and Gianluca Li Puma. "A light-management film layer induces dramatically enhanced acetate production in photo-assisted microbial electrosynthesis systems." Applied Catalysis B: Environmental, December 2022, 122247. http://dx.doi.org/10.1016/j.apcatb.2022.122247.

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Cai, Weiwei, Wenzong Liu, Bo Wang, Hong Yao, Awoke Guadie, and Aijie Wang. "Semiquantitative Detection of Hydrogen-Associated or Hydrogen-Free Electron Transfer within Methanogenic Biofilm of Microbial Electrosynthesis." Applied and Environmental Microbiology 86, no. 17 (June 19, 2020). http://dx.doi.org/10.1128/aem.01056-20.

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ABSTRACT Hydrogen-entangled electron transfer has been verified as an important extracellular pathway of sharing reducing equivalents to regulate biofilm activities within a diversely anaerobic environment, especially in microbial electrosynthesis systems. However, with a lack of useful methods for in situ hydrogen detection in cathodic biofilms, the role of hydrogen involvement in electron transfer is still debatable. Here, a cathodic biofilm was constructed in CH4-produced microbial electrosynthesis reactors, in which the hydrogen evolution dynamic was analyzed to confirm the presence of hydrogen-associated electron transfer near the cathode within a micrometer scale. Fluorescent in situ hybridization images indicated that a colocalized community of archaea and bacteria developed within a 58.10-μm-thick biofilm at the cathode, suggesting that the hydrogen gradient detected by the microsensor was consumed by the collaboration of bacteria and archaea. Coupling of a microsensor and cyclic voltammetry test further provided semiquantitative results of the hydrogen-associated contribution to methane generation (around 21.20% ± 1.57% at a potential of −0.5 V to −0.69 V). This finding provides deep insight into the mechanism of electron transfer in biofilm on conductive materials. IMPORTANCE Electron transfer from an electrode to biofilm is of great interest to the fields of microbial electrochemical technology, bioremediation, and methanogenesis. It has a promising potential application to boost more value-added products or pollutant degradation. Importantly, the ability of microbes to obtain electrons from electrodes and utilize them brings new insight into direct interspecies electron transfer during methanogenesis. Previous studies verified the direct pathway of electron transfer from the electrode to a pure-culture bacterium, but it was rarely reported how the methanogenic biofilm of mixed cultures shares electrons by a hydrogen-associated or hydrogen-free pathway. In the current study, a combination method of microsensor and cyclic voltammetry successfully semiquantified the role of hydrogen in electron transfer from an electrode to methanogenic biofilm.

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Winkelhorst, Marijn, Oriol Cabau-Peinado, Adrie J. J. Straathof, and Ludovic Jourdin. "Biomass-specific rates as key performance indicators: A nitrogen balancing method for biofilm-based electrochemical conversion." Frontiers in Bioengineering and Biotechnology 11 (January 19, 2023). http://dx.doi.org/10.3389/fbioe.2023.1096086.

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Microbial electrochemical technologies (METs) employ microorganisms utilizing solid-state electrodes as either electron sink or electron source, such as in microbial electrosynthesis (MES). METs reaction rate is traditionally normalized to the electrode dimensions or to the electrolyte volume, but should also be normalized to biomass amount present in the system at any given time. In biofilm-based systems, a major challenge is to determine the biomass amount in a non-destructive manner, especially in systems operated in continuous mode and using 3D electrodes. We developed a simple method using a nitrogen balance and optical density to determine the amount of microorganisms in biofilm and in suspension at any given time. For four MES reactors converting CO2 to carboxylates, >99% of the biomass was present as biofilm after 69 days of reactor operation. After a lag phase, the biomass-specific growth rate had increased to 0.12–0.16 days−1. After 100 days of operation, growth became insignificant. Biomass-specific production rates of carboxylates varied between 0.08–0.37 molC molX−1d−1. Using biomass-specific rates, one can more effectively assess the performance of MES, identify its limitations, and compare it to other fermentation technologies.

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Luo, Jiahao, Qianqian Yuan, Yufeng Mao, Fan Wei, Juntao Zhao, Wentong Yu, Shutian Kong, et al. "Reconstruction of a Genome-Scale Metabolic Network for Shewanella oneidensis MR-1 and Analysis of its Metabolic Potential for Bioelectrochemical Systems." Frontiers in Bioengineering and Biotechnology 10 (May 12, 2022). http://dx.doi.org/10.3389/fbioe.2022.913077.

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Bioelectrochemical systems (BESs) based on Shewanella oneidensis MR-1 offer great promise for sustainable energy/chemical production, but the low rate of electron generation remains a crucial bottleneck preventing their industrial application. Here, we reconstructed a genome-scale metabolic model of MR-1 to provide a strong theoretical basis for novel BES applications. The model iLJ1162, comprising 1,162 genes, 1,818 metabolites and 2,084 reactions, accurately predicted cellular growth using a variety of substrates with 86.9% agreement with experimental results, which is significantly higher than the previously published models iMR1_799 and iSO783. The simulation of microbial fuel cells indicated that expanding the substrate spectrum of MR-1 to highly reduced feedstocks, such as glucose and glycerol, would be beneficial for electron generation. In addition, 31 metabolic engineering targets were predicted to improve electricity production, three of which have been experimentally demonstrated, while the remainder are potential targets for modification. Two potential electron transfer pathways were identified, which could be new engineering targets for increasing the electricity production capacity of MR-1. Finally, the iLJ1162 model was used to simulate the optimal biosynthetic pathways for six platform chemicals based on the MR-1 chassis in microbial electrosynthesis systems. These results offer guidance for rational design of novel BESs.

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Lopes, Adriana Carla de Oliveira, and Fabiane Caxico de Abreu. "Utilization of carbon nanotubes in hydrogen electrosynthesis from tropical fruit fermentation." Matéria (Rio de Janeiro) 25, no. 3 (2020). http://dx.doi.org/10.1590/s1517-707620200003.1121.

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ABSTRACT The use of fossil fuels, especially oil and gas, has accelerated in recent years, resulting in the global energy crisis. The fermentative biological process is a sustainable way to produce hydrogen, as it can use as a substrate various types of carbohydrate-rich industrial and household waste such as fruit, minimizing but not completely eliminating the problems caused by improper disposal of this material. From a perspective of energy conservation and use of renewable sources for energy generation, this work aims to contribute to the identification of the use of a currently unused portion of energy, optimizing hydrogen production from a fuel cell. microbial. The main nanomaterial used in electrolysis was carbon nanotubes (CNT) incorporated into carbon felt (CF). Cyclic voltammetry studies were also performed on three electrode systems: vitreous carbon electrode as working electrode, platinum electrode as auxiliary electrode and Ag / AgCl / Cl- as reference electrode. An electrochemical cell formed by two separate compartments was constructed. Before starting the electrolysis experiment, an experimental design was performed using the complete factorial design technique to analyze the influence of the variables selected for this study. The independent variables selected were: Tropical fruit liquor concentration in %v/v, type of working electrode, electrolysis time and pH of the electrolyte medium. The observed variable was the concentration in% v / v of the hydrogen gas obtained in the electrolysis. After the results of the tests, it was concluded that carbon nanotubes can be used as working electrode, presenting success in the hydrogen production process and that the pH of the electrolytic medium has a strong influence on this process. The present work was concluded presenting an alternative way in the production of a renewable energy source.

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Xu, Ning, Tai-Lin Wang, Wen-Jie Li, Yan Wang, Jie-Jie Chen, and Jun Liu. "Tuning Redox Potential of Anthraquinone-2-Sulfonate (AQS) by Chemical Modification to Facilitate Electron Transfer From Electrodes in Shewanella oneidensis." Frontiers in Bioengineering and Biotechnology 9 (August 10, 2021). http://dx.doi.org/10.3389/fbioe.2021.705414.

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Bioelectrochemical systems (BESs) are emerging as attractive routes for sustainable energy generation, environmental remediation, bio-based chemical production and beyond. Electron shuttles (ESs) can be reversibly oxidized and reduced among multiple redox reactions, thereby assisting extracellular electron transfer (EET) process in BESs. Here, we explored the effects of 14 ESs on EET in Shewanella oneidensis MR-1, and found that anthraquinone-2-sulfonate (AQS) led to the highest cathodic current density, total charge production and reduction product formation. Subsequently, we showed that the introduction of -OH or -NH2 group into AQS at position one obviously affected redox potentials. The AQS-1-NH2 exhibited a lower redox potential and a higher Coulombic efficiency compared to AQS, revealing that the ESs with a more negative potential are conducive to minimize energy losses and improve the reduction of electron acceptor. Additionally, the cytochromes MtrA and MtrB were required for optimal AQS-mediated EET of S. oneidensis MR-1. This study will provide new clues for rational design of efficient ESs in microbial electrosynthesis.

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Izadi, Paniz, Jean-Marie Fontmorin, Alexiane Godain, Eileen H. Yu, and Ian M. Head. "Parameters influencing the development of highly conductive and efficient biofilm during microbial electrosynthesis: the importance of applied potential and inorganic carbon source." npj Biofilms and Microbiomes 6, no. 1 (October 14, 2020). http://dx.doi.org/10.1038/s41522-020-00151-x.

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Abstract Cathode-driven applications of bio-electrochemical systems (BESs) have the potential to transform CO2 into value-added chemicals using microorganisms. However, their commercialisation is limited as biocathodes in BESs are characterised by slow start-up and low efficiency. Understanding biosynthesis pathways, electron transfer mechanisms and the effect of operational variables on microbial electrosynthesis (MES) is of fundamental importance to advance these applications of a system that has the capacity to convert CO2 to organics and is potentially sustainable. In this work, we demonstrate that cathodic potential and inorganic carbon source are keys for the development of a dense and conductive biofilm that ensures high efficiency in the overall system. Applying the cathodic potential of −1.0 V vs. Ag/AgCl and providing only gaseous CO2 in our system, a dense biofilm dominated by Acetobacterium (ca. 50% of biofilm) was formed. The superior biofilm density was significantly correlated with a higher production yield of organic chemicals, particularly acetate. Together, a significant decrease in the H2 evolution overpotential (by 200 mV) and abundant nifH genes within the biofilm were observed. This can only be mechanistically explained if intracellular hydrogen production with direct electron uptake from the cathode via nitrogenase within bacterial cells is occurring in addition to the commonly observed extracellular H2 production. Indeed, the enzymatic activity within the biofilm accelerated the electron transfer. This was evidenced by an increase in the coulombic efficiency (ca. 69%) and a 10-fold decrease in the charge transfer resistance. This is the first report of such a significant decrease in the charge resistance via the development of a highly conductive biofilm during MES. The results highlight the fundamental importance of maintaining a highly active autotrophic Acetobacterium population through feeding CO2 in gaseous form, which its dominance in the biocathode leads to a higher efficiency of the system.

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Alqahtani, Manal F., Suman Bajracharya, Krishna P. Katuri, Muhammad Ali, Jiajie Xu, Mohammed S. Alarawi, and Pascal E. Saikaly. "Enrichment of salt-tolerant CO2–fixing communities in microbial electrosynthesis systems using porous ceramic hollow tube wrapped with carbon cloth as cathode and for CO2 supply." Science of The Total Environment, October 2020, 142668. http://dx.doi.org/10.1016/j.scitotenv.2020.142668.

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Morgado, Leonor, and Carlos A. Salgueiro. "Elucidation of complex respiratory chains: a straightforward strategy to monitor electron transfer between cytochromes." Metallomics 14, no. 4 (February 28, 2022). http://dx.doi.org/10.1093/mtomcs/mfac012.

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Abstract Cytochromes are electron transfer (ET) proteins essential in various biological systems, playing crucial roles in the respiratory chains of bacteria. These proteins are particularly abundant in electrogenic microorganisms and are responsible for the efficient delivery of electrons to the cells’ exterior. The capability of sending electrons outside the cells open new avenues to be explored for emerging biotechnological applications in bioremediation, microbial electrosynthesis, and bioenergy fields. To develop these applications, it is critical to identify the different redox partners and to elucidate the stepwise ET along the respiratory paths. However, investigating direct ET events between proteins with identical features in nearly all spectroscopic techniques is extremely challenging. Nuclear magnetic resonance (NMR) spectroscopy offers the possibility to overcome this difficulty by analysing the alterations of the spectral signatures of each protein caused by electron exchange events. The uncrowded NMR spectral regions containing the heme resonances of the cytochromes display unique and distinct signatures in the reduced and oxidized states, which can be explored to monitor ET within the redox complex. In this study, we present a strategy for a fast and straightforward monitorization of ET between c-type cytochromes, using as model a triheme periplasmic cytochrome and a membrane-associated monoheme cytochrome from the electrogenic bacterium Geobacter sulfurreducens. The comparison between the 1D 1H NMR spectra obtained for samples containing the two cytochromes and for samples containing the individual proteins clearly demonstrated a unidirectional ET within the redox complex. This strategy provides a simple and straightforward means to elucidate complex biologic respiratory ET chains.

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