Frauke Kracke

All Publications

• Designing a Zn-Ag Catalyst Matrix and Electrolyzer System for CO2 Conversion to CO and Beyond. Advanced materials (Deerfield Beach, Fla.) Lamaison, S., Wakerley, D., Kracke, F., Moore, T., Zhou, L., Lee, D. U., Wang, L., Hubert, M. A., Aviles Acosta, J. E., Gregoire, J. M., Duoss, E. B., Baker, S., Beck, V. A., Spormann, A. M., Fontecave, M., Hahn, C., Jaramillo, T. F. 2021: e2103963

  Abstract

  CO2 emissions can be transformed into high-added-value commodities through CO2 electrocatalysis; however, efficient low-cost electrocatalysts are needed for global scale-up. Inspired by other emerging technologies, the authors report the development of a gas diffusion electrode containing highly dispersed Ag sites in a low-cost Zn matrix. This catalyst shows unprecedented Ag mass activity for CO production: -614mAcm-2 at 0.17mgof Ag. Subsequent electrolyte engineering demonstrates that halide anions can further improve stability and activity of the Zn-Ag catalyst, outperforming pure Ag and Au. Membrane electrode assemblies are constructed and coupled to a microbial process that converts the CO to acetate and ethanol. Combined, these concepts present pathways to design catalysts and systems for CO2 conversion toward sought-after products.

  View details for DOI 10.1002/adma.202103963

  View details for PubMedID 34672402

• In situelectrochemical H(2)production for efficient and stable power-to-gas electromethanogenesis GREEN CHEMISTRY Kracke, F., Deutzmann, J. S., Gu, W., Spormann, A. M. 2020; 22 (18): 6194–6203

  View details for DOI 10.1039/d0gc01894e

  View details for Web of Science ID 000571356300028

• Microbial electron transport and energy conservation - the foundation for optimizing bioelectrochemical systems FRONTIERS IN MICROBIOLOGY Kracke, F., Vassilev, I., Kroemer, J. O. 2015; 6

  Abstract

  Microbial electrochemical techniques describe a variety of emerging technologies that use electrode-bacteria interactions for biotechnology applications including the production of electricity, waste and wastewater treatment, bioremediation and the production of valuable products. Central in each application is the ability of the microbial catalyst to interact with external electron acceptors and/or donors and its metabolic properties that enable the combination of electron transport and carbon metabolism. And here also lies the key challenge. A wide range of microbes has been discovered to be able to exchange electrons with solid surfaces or mediators but only a few have been studied in depth. Especially electron transfer mechanisms from cathodes towards the microbial organism are poorly understood but are essential for many applications such as microbial electrosynthesis. We analyze the different electron transport chains that nature offers for organisms such as metal respiring bacteria and acetogens, but also standard biotechnological organisms currently used in bio-production. Special focus lies on the essential connection of redox and energy metabolism, which is often ignored when studying bioelectrochemical systems. The possibility of extracellular electron exchange at different points in each organism is discussed regarding required redox potentials and effect on cellular redox and energy levels. Key compounds such as electron carriers (e.g., cytochromes, ferredoxin, quinones, flavins) are identified and analyzed regarding their possible role in electrode-microbe interactions. This work summarizes our current knowledge on electron transport processes and uses a theoretical approach to predict the impact of different modes of transfer on the energy metabolism. As such it adds an important piece of fundamental understanding of microbial electron transport possibilities to the research community and will help to optimize and advance bioelectrochemical techniques.

  View details for DOI 10.3389/fmicb.2015.00575

  View details for Web of Science ID 000356352000001

  View details for PubMedID 26124754

• In situ electrochemical H-2 production for efficient and stable power-to-gas electromethanogenesis (vol 22, pg 6194, 2020) GREEN CHEMISTRY Kracke, F., Deutzmann, J. S., Gu, W., Spormann, A. M. 2021

  View details for DOI 10.1039/d1gc90069b

  View details for Web of Science ID 000670547200001

• Efficient Hydrogen Delivery for Microbial Electrosynthesis via 3D-Printed Cathodes. Frontiers in microbiology Kracke, F., Deutzmann, J. S., Jayathilake, B. S., Pang, S. H., Chandrasekaran, S., Baker, S. E., Spormann, A. M. 2021; 12: 696473

  Abstract

  The efficient delivery of electrochemically in situ produced H2 can be a key advantage of microbial electrosynthesis over traditional gas fermentation. However, the technical details of how to supply large amounts of electric current per volume in a biocompatible manner remain unresolved. Here, we explored for the first time the flexibility of complex 3D-printed custom electrodes to fine tune H2 delivery during microbial electrosynthesis. Using a model system for H2-mediated electromethanogenesis comprised of 3D fabricated carbon aerogel cathodes plated with nickel-molybdenum and Methanococcus maripaludis, we showed that novel 3D-printed cathodes facilitated sustained and efficient electromethanogenesis from electricity and CO2 at an unprecedented volumetric production rate of 2.2 L CH4 /L catholyte /day and at a coulombic efficiency of 99%. Importantly, our experiments revealed that the efficiency of this process strongly depends on the current density. At identical total current supplied, larger surface area cathodes enabled higher methane production and minimized escape of H2. Specifically, low current density (<1 mA/cm2) enabled by high surface area cathodes was found to be critical for fast start-up times of the microbial culture, stable steady state performance, and high coulombic efficiencies. Our data demonstrate that 3D-printing of electrodes presents a promising design tool to mitigate effects of bubble formation and local pH gradients within the boundary layer and, thus, resolve key critical limitations for in situ electron delivery in microbial electrosynthesis.

  View details for DOI 10.3389/fmicb.2021.696473

  View details for PubMedID 34413839

• Low-Cost Clamp-On Photometers (ClampOD) and Tube Photometers (TubeOD) for Online Cell Density Determination. Frontiers in microbiology Deutzmann, J. S., Callander, G., Gu, W., Muller, A. L., McCully, A. L., Ahn, J. K., Kracke, F., Spormann, A. M. 1800; 12: 790576

  Abstract

  Optical density (OD) measurement is the gold standard to estimate microbial cell density in aqueous systems. Recording microbial growth curves is essential to assess substrate utilization, gauge sensitivity to inhibitors or toxins, or determine the perfect sampling point. Manual sampling for cuvette-photometer-based measurements can cause disturbances and impact growth, especially for strictly anaerobic or thermophilic microbes. For slow growing microbes, manual sampling can cause data gaps that complicate analysis. Online OD measurement systems provide a solution, but are often expensive and ill-suited for applications such as monitoring microbial growth in custom or larger anaerobic vessels. Furthermore, growth measurements of thermophilic cultures are limited by the heat sensitivity of complex electronics. Here, we present two simple, low-cost, self-assembled photometers-a "TubeOD" for online measurement of anaerobic and thermophilic cultures in Hungate tubes and a "ClampOD" that can be attached to virtually any transparent growth vessel. Both OD-meters can be calibrated in minutes. We detail the manufacturing and calibration procedure and demonstrate continuous acquisition of high quality cell density data of a variety of microbes, including strict anaerobes, a thermophile, and gas-utilizing strains in various glassware. When calibrated and operated within their detection limits (ca. 0.3-90% of the photosensor voltage range), these self-build OD-meters can be used for continuous measurement of microbial growth in a variety of applications, thereby, simplifying and enhancing everyday lab operations.

  View details for DOI 10.3389/fmicb.2021.790576

  View details for PubMedID 35095803

• Robust and biocompatible catalysts for efficient hydrogen-driven microbial electrosynthesis COMMUNICATIONS CHEMISTRY Kracke, F., Wong, A., Maegaard, K., Deutzmann, J. S., Hubert, M. A., Hahn, C., Jaramillo, T. F., Spormann, A. M. 2019; 2

  View details for DOI 10.1038/s42004-019-0145-0

  View details for Web of Science ID 000465438600001

• Microbial electrosynthesis system with dual biocathode arrangement for simultaneous acetogenesis, solventogenesis and carbon chain elongation. Chemical communications (Cambridge, England) Vassilev, I., Kracke, F., Freguia, S., Keller, J., Kromer, J. O., Ledezma, P., Virdis, B. 2019

  Abstract

  A microbial electrosynthesis cell comprising two biological cathode chambers sharing the same anode compartment is used to promote the production of C2-C4 carboxylic acids and alcohols from carbon dioxide. Each cathode chamber provides ideal pH conditions to favor acetogenesis/carbon chain elongation (pH = 6.9), and solventogenesis (pH = 4.9), respectively, without the requirement of external acid/base dosing.

  View details for DOI 10.1039/c9cc00208a

  View details for PubMedID 30911739

• Metabolic Network Analysis of Microbial Methane Utilization for Biomass Formation and Upgrading to Bio-Fuels FRONTIERS IN ENERGY RESEARCH Averesch, N. H., Kracke, F. 2018; 6

  View details for DOI 10.3389/fenrg.2018.00106

  View details for Web of Science ID 000447328000001

• Balancing cellular redox metabolism in microbial electrosynthesis and electro fermentation - A chance for metabolic engineering METABOLIC ENGINEERING Kracke, F., Lai, B., Yu, S., Kroemer, J. O. 2018; 45: 109–20

  Abstract

  More and more microbes are discovered that are capable of extracellular electron transfer, a process in which they use external electrodes as electron donors or acceptors for metabolic reactions. This feature can be used to overcome cellular redox limitations and thus optimizing microbial production. The technologies, termed microbial electrosynthesis and electro-fermentation, have the potential to open novel bio-electro production platforms from sustainable energy and carbon sources. However, the performance of reported systems is currently limited by low electron transport rates between microbes and electrodes and our limited ability for targeted engineering of these systems due to remaining knowledge gaps about the underlying fundamental processes. Metabolic engineering offers many opportunities to optimize these processes, for instance by genetic engineering of pathways for electron transfer on the one hand and target product synthesis on the other hand. With this review, we summarize the status quo of knowledge and engineering attempts around chemical production in bio-electrochemical systems from a microbe perspective. Challenges associated with the introduction or enhancement of extracellular electron transfer capabilities into production hosts versus the engineering of target compound synthesis pathways in natural exoelectrogens are discussed. Recent advances of the research community in both directions are examined critically. Further, systems biology approaches, for instance using metabolic modelling, are examined for their potential to provide insight into fundamental processes and to identify targets for metabolic engineering.

  View details for PubMedID 29229581

• Predicting and experimental evaluating bio-electrochemical synthesis - A case study with Clostridium kluyveri. Bioelectrochemistry (Amsterdam, Netherlands) Koch, C., Kuchenbuch, A., Kracke, F., Bernhardt, P. V., Krömer, J., Harnisch, F. 2017; 118: 114-122

  Abstract

  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)]3+) were tested for their toxicity and electro-fermentations were performed in 1L 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.

  View details for DOI 10.1016/j.bioelechem.2017.07.009

  View details for PubMedID 28800557

• Quantitative analysis of aromatics for synthetic biology using liquid chromatography Biotechnology Journal Lai, B., Plan, M. R., Averesch, N. J., Yu, S., Kracke, F., Lekieffre, N., Bydder, S., Hodson, M. P., Winter, G., Krömer, J. O. 2017; 12 (1)

  Abstract

  The replacement of petrochemical aromatics with bio-based molecules is a key area of current biotechnology research. To date, a small number of aromatics have been produced by recombinant bacteria in laboratory scale while industrial production still requires further strain development. While each study includes some distinct analytical methodology to quantify certain aromatics, a method that can reliably quantify a great number of aromatic products and relevant pathway intermediates is needed to accelerate strain development. In this study, we developed a robust reverse phase high performance liquid chromatography method to quantify a wide range of aromatic metabolites present in host microorganisms using the shikimate pathway, which is the major metabolic pathway for biosynthesis of aromatics. Twenty-three metabolites can be quantified precisely with the optimized method using standard HPLC equipment and UV detection, with the mobile phase used for chromatography also compatible with mass spectrometry (MS). The limit of quantification/detection is as low as 10-10 to 10-13 mol, respectively, which makes this method feasible for quantification of intracellular metabolites. This method covers most metabolic routes for aromatics biosynthesis, it is inexpensive, robust, simple, precise and sensitive, and has been demonstrated on cell extracts from S. cerevisiae genetically engineered to overproduce aromatics.

  View details for DOI 10.1002/biot.201600269

• Balancing cellular redox metabolism in microbial electrosynthesis and electro fermentation – A chance for metabolic engineering Metabolic Engineering Kracke, F., Lai, B., Yu, S., Krömer, J. O. 2017
• Predicting and experimental evaluating bio-electrochemical synthesis — A case study with Clostridium kluyveri Bioelectrochemistry Koch, C., Kuchenbuch, A., Kracke, F., Krömer, J. O., Harnisch, F. 2017

  View details for DOI 10.1016/j.bioelechem.2017.07.009

• Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply Biotechnology for Biofuels Kracke, F., Virdis, V., Bernhardt, P. V., Rabaey, K., Krömer, J. O. 2016; 9 (1): 249

  View details for DOI 10.1186/s13068-016-0663-2

• Nontoxic, Hydrophilic Cationic Polymers-Identified as Class of Antimicrobial Polymers MACROMOLECULAR BIOSCIENCE Strassburg, A., Kracke, F., Wenners, J., Jemeljanova, A., Kuepper, J., Petersen, H., Tiller, J. C. 2015; 15 (12): 1710-1723

  Abstract

  Amphiphilic polycations are an alternative to biocides but also toxic to mammalian cells. Antimicrobially active hydrophilic polycations based on 1,4-dibromo-2-butene and tetramethyl-1,3-propanediamine named PBI are not hemotoxic for porcine red blood cells with a hemocytotoxicity (HC50) of more than 40,000 μg · mL(-1). They are quickly killing bacterial cells at their MIC (minimal inhibitory concentration). The highest found selectivity HC50 /MIC is more than 20,000 for S. epidermidis. Investigations on sequentially prepared PBIs with defined molecular weight Mn and tailored end groups revealed that there is a dependence of antimicrobial activity and selectivity on Mn and nature of the end groups.

  View details for DOI 10.1002/mabi.201500207

  View details for Web of Science ID 000368456500010

  View details for PubMedID 26240988

• Electrifying white biotechnology: engineering and economic potential of electricity-driven bio-production. ChemSusChem Harnisch, F., Rosa, L. F., Kracke, F., Virdis, B., Krömer, J. O. 2015; 8 (5): 758-766

  Abstract

  The production of fuels and chemicals by electricity-driven bio-production (i.e., using electric energy to drive biosynthesis) holds great promises. However, this electrification of white biotechnology is particularly challenging to achieve because of the different optimal operating conditions of electrochemical and biochemical reactions. In this article, we address the technical parameters and obstacles to be taken into account when engineering microbial bioelectrochemical systems (BES) for bio-production. In addition, BES-based bio-production processes reported in the literature are compared against industrial needs showing that a still large gap has to be closed. Finally, the feasibility of BES bio-production is analysed based on bulk electricity prices. Using the example of lysine production from sucrose, we demonstrate that there is a realistic market potential as cost savings of 8.4 % (in EU) and 18.0 % (in US) could be anticipated, if the necessary yields can be obtained.

  View details for DOI 10.1002/cssc.201402736

  View details for PubMedID 25504806

• Identifying target processes for microbial electrosynthesis by elementary mode analysis. BMC bioinformatics Kracke, F., Krömer, J. O. 2014; 15: 410-?

  Abstract

  Microbial electrosynthesis and electro fermentation are techniques that aim to optimize microbial production of chemicals and fuels by regulating the cellular redox balance via interaction with electrodes. While the concept is known for decades major knowledge gaps remain, which make it hard to evaluate its biotechnological potential. Here we present an in silico approach to identify beneficial production processes for electro fermentation by elementary mode analysis. Since the fundamentals of electron transport between electrodes and microbes have not been fully uncovered yet, we propose different options and discuss their impact on biomass and product yields.For the first time 20 different valuable products were screened for their potential to show increased yields during anaerobic electrically enhanced fermentation. Surprisingly we found that an increase in product formation by electrical enhancement is not necessarily dependent on the degree of reduction of the product but rather the metabolic pathway it is derived from. We present a variety of beneficial processes with product yield increases of maximal 36% in reductive and 84% in oxidative fermentations and final theoretical product yields up to 100%. This includes compounds that are already produced at industrial scale such as succinic acid, lysine and diaminopentane as well as potential novel bio-commodities such as isoprene, para-hydroxybenzoic acid and para-aminobenzoic acid. Furthermore, it is shown that the way of electron transport has major impact on achievable biomass and product yields. The coupling of electron transport to energy conservation could be identified as crucial for most processes.This study introduces a powerful tool to determine beneficial substrate and product combinations for electro-fermentation. It also highlights that the maximal yield achievable by bio electrochemical techniques depends strongly on the actual electron transport mechanisms. Therefore it is of great importance to reveal the involved fundamental processes to be able to optimize and advance electro fermentations beyond the level of lab-scale studies.

  View details for DOI 10.1186/s12859-014-0410-2

  View details for PubMedID 25547630