Reactors for microbial electrobiotechnology

From the first electromicrobial experiment to a sophisticated microbial electrochemical process - it all takes place in a reactor. Whereas the reactor design and materials used strongly influence the obtained results, there are no common platforms for MES reactors. This is a critical convention gap, as cross-comparison and benchmarking among MES as well as MES vs. conventional biotechnological processes is needed. Only knowledge driven engineering of MES reactors will pave the way to application and commercialization. In this chapter we first assess the requirements on reactors to be used for bioelectrochemical systems as well as potential losses caused by the reactor design. Subsequently, we compile the main types and designs of reactors used for MES so far, starting from simple H-cells to stirred tank reactors. We conclude with a discussion on the weaknesses and strengths of the existing types of reactors for bioelectrochemical systems that are scored on design criteria and draw conclusions for the future engineering of MES reactors. [GRAPHICS]

Trophic networks improve the performance of microbial anodes treating wastewater

Microbial anodes represent a distinct ecological niche that is characterized mainly by the terminal electron acceptor, i.e., the anode potential, and the substrate, i.e., the electron source. Here, we determine the performance and the biofilm community of anode microbiomes while using substrates of increasing complexity (organic acids or organic acids and sugar or real domestic wastewater) to mimic different, practically relevant, trophic levels. α-Diversity values increased with substrate complexity. In addition, the higher abundance value of Deltaproteobacteria in the biofilms corresponds to higher reactor performance (i.e., COD removal, current density, and Coulombic efficiency). In reactors exploiting real wastewater, the diversity of the planktonic microorganisms was only little affected. Microbiome network analysis revealed two important clusters for reactor performance as well as performance-independent pathogen-containing clusters. Interestingly, Geobacter was not found to be integrated in the network underlining its outstanding individual ecological role in line with its importance for the efficiency of the electron harvest for all reactors. The microbiome analysis of different trophic levels and their temporal development from initial colonization to stable treatment demonstrate important principles for the implementation of microbial anodes for wastewater treatment

Use of SWATH mass spectrometry for quantitative proteomic investigation of Shewanella oneidensis MR-1 biofilms grown on graphite cloth electrodes

Quantitative proteomics from low biomass, biofilm samples is not well documented. In this study we show successful use of SWATH-MS for quantitative proteomic analysis of a microbial electrochemically active biofilm. Shewanella oneidensis MR-1 was grown on carbon cloth electrodes under continuous anodic electrochemical polarizations in a bioelectrochemical system (BES). Using lactate as the electron donor, anodes serving as terminal microbial electron acceptors were operated at three different electrode potentials (+0.71 V, +0.21 V & -0.19V vs. SHE) and the development of catalytic activity was monitored by measuring the current traces over time. Once maximum current was reached (usually within 21-29 h) the electrochemical systems were shut off and biofilm proteins were extracted from the electrodes for proteomic assessment. SWATH-MS analysis identified 704 proteins, and quantitative comparison was made of those associated with tricarboxcylic acid (TCA) cycle. Metabolic differences detected between the biofilms suggested a branching of the S. oneidensis TCA cycle when grown at the different electrode potentials. In addition, the higher abundance of enzymes involved in the TCA cycle at higher potential indicates an increase in metabolic activity, which is expected given the assumed higher energy gains. This study demonstrates high numbers of identifications on BES biofilm samples can be achieved in comparison to what is currently reported. This is most likely due to the minimal preparation steps required for SWATH-MS. (C) 2014 Elsevier GmbH. All rights reserved

Application of gas diffusion electrodes in bioeconomy: An update

The transition of today's fossil fuel based chemical industry toward sustainable production requires improvement of established production processes as well as development of new sustainable and bio-based synthesis routes within a circular economy. Thereby, the combination of electrochemical and biotechnological advantages in such routes represents one important keystone. For the electrochemical generation of reactants from gaseous substrates such as O2 or CO2, gas diffusion electrodes (GDE) represent the electrodes of choice since they overcome solubility-based mass transport limitations. Within this article, we illustrate the architecture, function principle and fabrication of GDE. We highlight the application of GDE for conversion of CO2 using abiotic catalysts for subsequent biosynthesis as well as the application of microbial catalysts at GDE for CO2 conversion. The reduction of oxygen at GDE is summarized for the application of oxygen depolarized cathodes in microbial fuel cells and generation of H2O2 to drive enzymatic reactions. Finally, engineering aspects such as scale-up and the modeling of GDE-based processes are described. This review presents an update on the application of GDE in bio-based production systems and emphasizes their large potential for sustainable development of new pathways in bioeconomy

Enhancing methane production from food waste fermentate using biochar. The added value of electrochemical testing in pre-selecting the most effective type of biochar

Background: Recent studies have suggested that addition of electrically conductive biochar particles is an effective strategy to improve the methanogenic conversion of waste organic substrates, by promoting syntrophic associations between acetogenic and methanogenic organisms based on interspecies electron transfer processes. However, the underlying fundamentals of the process are still largely speculative and, therefore, a priori identification, screening, and even design of suitable biochar materials for a given biotechnological process are not yet possible. Results: Here, three charcoal-like products (i.e., biochars) obtained from the pyrolysis of different lignocellulosic materials, (i.e., wheat bran pellets, coppiced woodlands, and orchard pruning) were tested for their capacity to enhance methane production from a food waste fermentate. In all biochar-supplemented (25 g/L) batch experiments, the complete methanogenic conversion of fermentate volatile fatty acids proceeded at a rate that was up to 5 times higher than that observed in the unamended (or sand-supplemented) controls. Fluorescent in situ hybridization analysis coupled with confocal laser scanning microscopy revealed an intimate association between archaea and bacteria around the biochar particles and provided a clear indication that biochar also shaped the composition of the microbial consortium. Based on the application of a suite of physico-chemical and electrochemical characterization techniques, we demonstrated that the positive effect of biochar is directly related to the electron-donating capacity (EDC) of the material, but is independent of its bulk electrical conductivity and specific surface area. The latter properties were all previously hypothesized to play a major role in the biochar-mediated interspecies electron transfer process in methanogenic consortia. Conclusions: Collectively, these results of this study suggest that for biochar addition in anaerobic digester operation, the screening and identification of the most suitable biochar material should be based on EDC determination, via simple electrochemical tests. © 2017 The Author(s)

Correction: In situ analysis of a silver nanoparticle-precipitating Shewanella biofilm by surface enhanced confocal Raman microscopy

Correction: In situ analysis of a silver nanoparticle-precipitating Shewanella biofilm by surface enhanced confocal Raman microscop

Predicting and experimental evaluating bio-electrochemical synthesis — A case study with Clostridium kluyveri

Microbial electrosynthesis is a highly promising application of microbial electrochemical technologies for the sustainable production of organic compounds. At the same time a multitude of questions need to be answered and challenges to be met. Central for its further development is using appropriate electroactive microorganisms and their efficient extracellular electron transfer (EET) as well as wiring of the metabolism to EET. Among others, Clostridia are believed to represent electroactive microbes being highly promising for microbial electrosynthesis. We investigated the potential steps and challenges for the bio-electrochemical fermentation (electro-fermentation) of mid-chain organic acids using Clostridium kluyveri. Starting from a metabolic model the potential limitations of the metabolism as well as beneficial scenarios for electrochemical stimulation were identified and experimentally investigated. C. kluyveri was shown to not be able to exchange electrons with an electrode directly. Therefore, exogenous mediators (2-hydroxy-1,4-naphthoquinone, potassium ferrocyanide, neutral red, methyl viologen, methylene blue, and the macrocyclic cobalt hexaamine [Co(trans-diammac)]) were tested for their toxicity and electro-fermentations were performed in 1\ua0L bioreactors covering 38 biotic and 8 abiotic runs. When using C. kluyveri and mediators, maximum absolute current densities higher than the abiotic controls were detected for all runs. At the same time, no significant impact on the cell metabolism (product formation, carbon recovery, growth rate) was found. From this observation, we deduce general potential limitations of electro-fermentations with C. kluyveri and discuss strategies to successfully overcome them

Erneuerbare Kraftstoffe für Mobilität und Industrie

Der nunmehr verabschiedete Klimaschutzplan mit 95% THG-Reduzierung bis 2050 gegenüber 1990 stellt alle Sektoren vor sehr große Herausforderungen. Zur schrittweisen Umsetzung der Klimaschutzziele (z. B. Verkehr 40 bis 42 % Treibhausgasminderung, Industrie 49 bis 51% jeweils bis 2030 gegenüber 1990) bedarf es nicht nur eines klaren politischen Willens, sondern auch konkreter rahmenpolitischer Umsetzungsmaßnahmen, die es der deutschen (Volks-)Wirtschaft in einer modernisierten und dekarbonisierten Welt erlauben, wettbewerbsfähig zu bleiben. Dabei sind nachhaltige erneuerbare Energieträger und Produkte für unterschiedliche Anwendungen wesentliche Bausteine. Im Sinne einer Puzzlestrategie bedarf es in dem insbesondere mit der Energiewende angeschobenen Transformationsprozess außerdem einer deutlich stärkeren Kopplung der einzelnen Sektoren. Hier verspricht die Kopplung von Biomassebiomasse- und strombasierte Technologien eine Reihe bislang ungenutzter Synergien, die es u. a. erlauben ein höheres Potenzial an erneuerbarem Kohlenstoff (C) zu erschließen. Dafür bedarf es einer technologieoffenen Weiterentwicklung, um bis 2050 Optionen in adäquaten Mengen am Markt zu etablieren sowie entsprechend flankierender Instrumente und Maßnahmen. Ein Instrument zur Frühindikation für Wettbewerbsfähigkeit im Kontext Nachhaltigkeit ist eine an die jeweiligen TRL/FRL-angepasste Technologiebewertung

Coupling an Electroactive Pseudomonas putida KT2440 with Bioelectrochemical Rhamnolipid Production

Sufficient supply of oxygen is amajor bottleneck in industrial biotechnological synthesis. One example is the heterologous production of rhamnolipids using Pseudomonas putida KT2440. Typically, the synthesis is accompanied by strong foam formation in the reactor vessel hampering the process. It is caused by the extensive bubbling needed to sustain the high respirative oxygen demand in the presence of the produced surfactants. One way to reduce the oxygen requirement is to enable the cells to use the anode of a bioelectrochemical system (BES) as an alternative sink for their metabolically derived electrons. We here used a P. putida KT2440 strain that interacts with the anode using mediated extracellular electron transfer via intrinsically produced phenazines, to performheterologous rhamnolipid production under oxygen limitation. The strain P. putida RL-PCA successfully produced 30.4 � 4.7mg/Lmono-rhamnolipids togetherwith 11.2 � 0.8mg/L of phenazine-1-carboxylic acid (PCA) in 500-mL benchtop BES reactors and 30.5 � 0.5 mg/L rhamnolipids accompanied by 25.7 � 8.0 mg/L PCA in electrode containing standard 1-L bioreactors. Hence, this study marks a first proof of concept to produce glycolipid surfactants in oxygen-limited BES with an industrially relevant strain

Dynamics of cathode-associated microbial communities and metabolite profiles in a glycerol-fed bioelectrochemical system

Electrical current can be used to supply reducing power to microbial metabolism. This phenomenon is typically studied in pure cultures with added redox mediators to transfer charge. Here, we investigate the development of a current-fed mixed microbial community fermenting glycerol at the cathode of a bioelectrochemical system in the absence of added mediators and identify correlations between microbial diversity and the respective product outcomes. Within 1 week of inoculation, a Citrobacter population represented 95 to 99% of the community and the metabolite profiles were dominated by 1,3-propanediol and ethanol. Over time, the Citrobacter population decreased in abundance while that of a Pectinatus population and the formation of propionate increased. After 6 weeks, several Clostridium populations and the production of valerate increased, which suggests that chain elongation was being performed. Current supply was stopped after 9 weeks and was associated with a decrease in glycerol degradation and alcohol formation. This decrease was reversed by resuming current supply; however, when hydrogen gas was bubbled through the reactor during open-circuit operation (open-circuit potential) as an alternative source of reducing power, glycerol degradation and metabolite production were unaffected. Cyclic voltammetry revealed that the community appeared to catalyze the hydrogen evolution reaction, leading to a +400-mV shift in its onset potential. Our results clearly demonstrate that current supply can alter fermentation profiles; however, further work is needed to determine the mechanisms behind this effect. In addition, operational conditions must be refined to gain greater control over community composition and metabolic outcomes