ORCID Profile
0000-0002-6684-9088
Current Organisations
University of Amsterdam
,
ETH Zurich
,
TU Dortmund University
,
AMC
,
Helmholtz-Gemeinschaft
,
University of Stuttgart
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Publications
Colloidal stability of capped silver nanoparticles in natural organic matter-containing electrolyte solutions
Publisher: Elsevier BV
Date: 07-2020
Metabolic response of Pseudomonas putida during redox biocatalysis in the presence of a second octanol phase
Publisher: Wiley
Date: 24-09-2008
DOI: 10.1111/J.1742-4658.2008.06648.X
Abstract: A key limitation of whole-cell redox biocatalysis for the production of valuable, specifically functionalized products is substrate roduct toxicity, which can potentially be overcome by using solvent-tolerant micro-organisms. To investigate the inter-relationship of solvent tolerance and energy-dependent biocatalysis, we established a model system for biocatalysis in the presence of toxic low logP(ow) solvents: recombinant solvent-tolerant Pseudomonas putida DOT-T1E catalyzing the stereospecific epoxidation of styrene in an aqueous/octanol two-liquid phase reaction medium. Using (13)C tracer based metabolic flux analysis, we investigated the central carbon and energy metabolism and quantified the NAD(P)H regeneration rate in the presence of toxic solvents and during redox biocatalysis, which both drastically increased the energy demands of solvent-tolerant P. putida. According to the driven by demand concept, the NAD(P)H regeneration rate was increased up to eightfold by two mechanisms: (a) an increase in glucose uptake rate without secretion of metabolic side products, and (b) reduced biomass formation. However, in the presence of octanol, only approximately 1% of the maximally observed NAD(P)H regeneration rate could be exploited for styrene epoxidation, of which the rate was more than threefold lower compared with operation with a non-toxic solvent. This points to a high energy and redox cofactor demand for cell maintenance, which limits redox biocatalysis in the presence of octanol. An estimated upper bound for the NAD(P)H regeneration rate available for biocatalysis suggests that cofactor availability does not limit redox biocatalysis under optimized conditions, for ex le, in the absence of toxic solvent, and illustrates the high metabolic capacity of solvent-tolerant P. putida. This study shows that solvent-tolerant P. putida have the remarkable ability to compensate for high energy demands by boosting their energy metabolism to levels up to an order of magnitude higher than those observed during unlimited growth.
Design and Implementation of the International Genetics and Translational Research in Transplantation Network
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 11-2015
Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO3 and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting
Publisher: MDPI AG
Date: 22-11-2021
Abstract: While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO3) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems.
Metabolic capacity estimation of Escherichia coli as a platform for redox biocatalysis: constraint‐based modeling and experimental verification
Publisher: Wiley
Date: 13-06-2008
DOI: 10.1002/BIT.21837
Abstract: Whole-cell redox biocatalysis relies on redox cofactor regeneration by the microbial host. Here, we applied flux balance analysis based on the Escherichia coli metabolic network to estimate maximal NADH regeneration rates. With this optimization criterion, simulations showed exclusive use of the pentose phosphate pathway at high rates of glucose catabolism, a flux distribution usually not found in wild-type cells. In silico, genetic perturbations indicated a strong dependency of NADH yield and formation rate on the underlying metabolic network structure. The linear dependency of measured epoxidation activities of recombinant central carbon metabolism mutants on glucose uptake rates and the linear correlation between measured activities and simulated NADH regeneration rates imply intracellular NADH shortage. Quantitative comparison of computationally predicted NADH regeneration and experimental epoxidation rates indicated that the achievable biocatalytic activity is determined by metabolic and enzymatic limitations including non-optimal flux distributions, high maintenance energy demands, energy spilling, byproduct formation, and uncoupling. The results are discussed in the context of cellular optimization of biotransformation processes and may guide a priori design of microbial cells as redox biocatalysts.
Technical‐scale biophotovoltaics for long‐term photo‐current generation from Synechocystis sp. PCC6803
Publisher: Wiley
Date: 05-05-2021
DOI: 10.1002/BIT.27784
Abstract: A carbon‐free energy supply is essential to sustain our future. Biophotovoltaics (BPV) provides a promising solution for hydrogen supply by directly coupling light‐driven water splitting to hydrogen formation using oxygenic photoautotrophic cyanobacteria. However, BPV is currently limited by its low photon‐to‐current efficiency, and current experimental setups at a miniaturized scale hinder the rational investigation of the process and thus system optimization. In this article, we developed and optimized a new technical‐scale (~250 ml working volume) BPV platform with defined and controllable operating parameters. Factors that interfered with reproducible and stable current output signals were identified and adapted. We found that the classical BG11 medium, used for the cultivation of cyanobacteria and also in many BPV studies, caused severe interferences in the bioelectrochemical experiments. An optimized nBG11 medium guaranteed a low and stable background current in the BPV reactor, regardless of the presence of light and/or mediators. As proof‐of‐principle, a very high long‐term light‐dependent current output (peak current of over 20 µA) was demonstrated in the new set‐up over 12 days with living Synechocystis sp. PCC6803 cells and validated with appropriate controls. These results report the first reliable BPV platform generating reproducible photocurrent while still allowing quantitative investigation, rational optimization, and scale‐up of BPV processes.
Growth of Pseudomonas taiwanensisVLB 120∆C biofilms in the presence of n‐butanol
Publisher: Wiley
Date: 03-10-2016
Response of Pseudomonas putida KT2440 to Increased NADH and ATP Demand
Publisher: American Society for Microbiology
Date: 15-09-2011
DOI: 10.1128/AEM.05588-11
Abstract: Adenosine phosphate and NAD cofactors play a vital role in the operation of cell metabolism, and their levels and ratios are carefully regulated in tight ranges. Perturbations of the consumption of these metabolites might have a great impact on cell metabolism and physiology. Here, we investigated the impact of increased ATP hydrolysis and NADH oxidation rates on the metabolism of Pseudomonas putida KT2440 by titration of 2,4-dinitrophenol (DNP) and overproduction of a water-forming NADH oxidase, respectively. Both perturbations resulted in a reduction of the biomass yield and, as a consequence of the uncoupling of catabolic and anabolic activities, in an lification of the net NADH regeneration rate. However, a stimulation of the specific carbon uptake rate was observed only when P. putida was challenged with very high 2,4-dinitrophenol concentrations and was comparatively unaffected by recombinant NADH oxidase activity. This behavior contrasts with the comparably sensitive performance described, for ex le, for Escherichia coli or Saccharomyces cerevisiae . The apparent robustness of P. putida metabolism indicates that it possesses a certain buffering capacity and a high flexibility to adapt to and counteract different stresses without showing a distinct phenotype. These findings are important, e.g., for the development of whole-cell redox biocatalytic processes that impose equivalent burdens on the cell metabolism: stoichiometric consumption of (reduced) redox cofactors and increased energy expenditures, due to the toxicity of the biocatalytic compounds.
Related Organisations
Related Funding Activities
No related grants have been discovered for Andreas Schmid.