Universität Stuttgart

Now showing 1 - 6 of 6

Open Access
Resolving heterogeneities in single and multiphase bioreactor systems - Predictive modelling tools towards successful scale-up
(2020) Kuschel, Maike; Takors, Ralf (Prof. Dr.-Ing.)
Open Access
Bioprocess development with Clostridium ljungdahlii based on metabolic modelling
(2023) Ankenbauer, Maria; Takors, Ralf (Prof. Dr.-Ing.)
Bacterial synthesis gas (syngas) fermentation offers a promising solution for the reduction of greenhouse gas emissions - the greatest challenge of today’s society. The substrate gas, which mainly consists of CO2, CO, and H2, represents an inexpensive feedstock originating from agricultural, industrial, and municipal wastes. It can be metabolized to a multitude of valuable commodity chemicals and biofuels using different autotrophic bacteria. With syngas fermentation, fossil-based resources are replaced with the simultaneous diminution of the greenhouse gas CO2 and usage of the waste gas CO. In this regard, Clostridium ljungdahlii (C. ljungdahlii) is a good representative of gas-fermenting acetogens, as it is natively endowed to convert syngas components into acetic acid, ethanol, 2,3-butanediol (2,3-BD) and lactate. In addition, C. ljungdahlii is genetically accessible and, therefore, a promising platform for the recombinant formation of high-value products like isobutanol. The autotrophic central metabolism of C. ljungdahlii refers to the Wood-Ljungdahl pathway (WLP), an ancient and energy-limited reductive pathway that relies on a proton gradient for ATP conservation. The conversion of reducing equivalents within this pathway is essential for the establishing of the proton gradient needed for ATP formation, and also for product formation based on several reductive steps starting from CO2. The provision of crucial reducing equivalents depends on the oxidation of the electron source in the substrate gas - CO via carbon monoxide dehydrogenase (CODH) or H2 by a bifurcating hydrogenase (HYD). Hence, for the optimized formation of natural and non-natural reduced products, it is decisive to thoroughly understand the cellular link between energy management, growth, by-product formation, and the electron availability in the substrate gas. In the framework of this thesis, controlled bioreactor batch cultivations with continuous gas supply in 2 L scale were performed to study the growth and product formation of C. ljungdahlii in dependence on varying substrate compositions. In addition, a stoichiometric metabolic model was manually reconstructed for subsequent analysis of intracellular carbon fluxes, redox and energy metabolism using flux balance analysis. Subsequently, the heterologous syngas-based isobutanol production of C. ljungdahlii was investigated. Finally, with regard to the scale-up of syngas fermentations to commercial scales, possible performance losses during CO-based cultivation of C. ljungdhalii in a 125 m3 bubble column reactor were analysed using a kinetic correlation model.
Open Access
Micro-aerobic production of isobutanol with Pseudomonas putida and investigation of its resilience to substrate limitations
(2022) Ankenbauer, Andreas; Takors, Ralf (Prof. Dr.-Ing.)
The transition from an economy based on fossil resources to a regenerative economy is imminent yet uncertain. Despite an awareness of the scarcity of fossil fuels and the increasing natural disasters due to climate change, the world’s renewable energy supply still constitutes less than 20% of the total energy supply. To reduce humankind’s carbon footprint, next-generation biofuels, such as ethanol or isobutanol, have the potential to revolutionize the transportation energy demand. These biofuels can be produced from renewable feedstock in large bioreactors using microorganisms. However, inhomogeneities, such as carbon or oxygen gradients in large-scale bioreactors, often limit the efficiency of such industrial bioprocesses. The soil bacterium Pseudomonas putida has the potential to supersede existing industrial workhorses like Escherichia coli or Corynebacterium glutamicum due to its natural tolerance towards alcohols, its versatile repertoire of stress responses, and its affinity to a broad range of substrates. This thesis aims to investigate the capability of isobutanol production in P. putida KT2440 and to explore its performance during large-scale stress.
Open Access
Identification of key regulatory interactions governing the growth rate in Corynebacterium glutamicum
(2024) Haas, Thorsten; Takors, Ralf (Prof. Dr.-Ing.)
The dissertation identifies key regulatory mechanisms governing the growth rate of Corynebacterium glutamicum.
Open Access
Scale-up of gas fermentations : modelling tools for risk minimisation
(2020) Siebler, Flora
The reduction of greenhouse gas emissions is a global endeavour supported by society, politics and industry. In recent years, circular economy, reducing the exploitation of fossil energy sources, have increased the demand for new solutions when producing commodities and fine chemicals. Caboxydotrophic fermentations with acetogenic bacteria are potential processes in order to reach these goals. They convert gaseous substrates such as CO, and CO2/H2 mixtures. However, gases as sole substrate are rather challenging, not only in small lab-scales but especially in large-scale. Transferring an efficient fermentation process from experimental to industrial scales often results in unpredictable performance losses. This study presents an in silico concept minimising possible risks in gas fermentations up-scaling. First, the economical feasibility of various fermentation methods is investigated. Then, two computational tools are presented using Clostridium ljungdahlii as model organism and synthesis gas as substrate in a 125 m3 bubble column reactor. The combination of economical investigation with modelling tools show high potential for successful scale-up of gas fermentations. With this concept feasibility, reactor design, operation mode and general risk minimisation can be analysed and specified.
Open Access
Investigation of the impact of different scale-up dependent stimuli on metabolism and population heterogeneity in Corynebacterium glutamicum
(2024) Eilingsfeld, Adrian; Takors, Ralf (Prof. Dr.-Ing.)
This thesis investigates the impact of elevated carbon dioxide levels on population heterogeneity in Corynebacterium glutamicum, a widely used industrial production host. Through a series of experiments involving cultivation at varying CO2 partial pressures, flow cytometry, and analysis of DNA content, the research reveals that increased CO2 exerts significant selection pressure, affecting growth rates and cell aggregation tendencies. Key findings indicate that higher growth rates speed up DNA replication levels, while elevated CO2 levels slow them down. The results contribute to understanding how CO2 influences population dynamics, providing insights for optimizing industrial bioprocesses and support Corynebacterium glutamicum as a robust production strain.

Universität Stuttgart

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