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Philipps-Universität Marburg
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Abstract
This work explores the critical challenge of enhancing natural carbon fixation to address the escalating issues of climate change, rising atmospheric CO2 levels, and global food shortages. At the heart of this challenge is the Calvin-Benson-Bassham cycle, the predominant pathway for CO2 fixation that evolved over 3 billion years ago. While this cycle is responsible for the incorporation of inorganic carbon into the global carbon cycle, its efficiency is compromised due to a side reaction with oxygen, leading to energy and carbon loss through a process known as photorespiration. Given the vital role of autotrophic CO2 fixation in the global carbon cycle, with an annual net fixation rate of 70 – 104 Gt carbon, and the increasing threat of greenhouse gas emissions due to rising CO2 levels in the atmosphere, there is an urgent need for innovative solutions to enhance carbon fixation efficiency.
This work focusses on two groundbreaking approaches aimed at optimizing photorespiration and overall carbon fixation rates. The first approach is based on the tartronyl-CoA (TaCo) pathway, a synthetic pathway designed to transform photorespiration from a carbon releasing to a carbon fixing process. Key to this pathway is the enzyme glycolyl-CoA carboxylase (GCC), which was engineered in this work towards reduced energy requirements and increased carboxylation rates through a machine learning-supported workflow. This resulted in the identification of novel GCC variants with 2-fold increased carboxylation rate and 60 % reduced energy demand, respectively, which are both suitable to offer improvements for the kinetic and thermodynamic properties of the TaCo pathway and highlight the potential of enzyme engineering in enhancing carbon fixation pathways.
The second approach focuses on the direct reduction of CO2 to formate, offering an alternative solution to replace the carbon releasing step of natural photorespiration. This led to the creation of the CORE cycle, a new-to-nature metabolic pathway capable of reducing CO2 under aerobic conditions and ambient CO2 levels, using NADPH as a reductant. The development process included in vitro testing of various pathway designs, enzyme screenings to realize new-to-nature reactions, structural investigation of key enzymes as well as their kinetic and mechanistic characterization, culminating in a pathway that operates efficiently under aerobic, ambient conditions.
The findings presented in this thesis significantly advance our understanding of CO2 fixation and propose viable strategies for improving carbon fixation efficiently and overcoming natural limitations. The successful engineering of the GCC enzyme and the establishment of the CORE cycle demonstrate the potential of synthetic biology and machine learning in addressing environmental challenges. These innovations not only offer a means to enhance crop yields and carbon fixation rates but also provide a versatile toolkit for tackling the climate crisis and food security issues.
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Dates
Created: 2024Issued: 2025-08-06Updated: 2025-08-06
Faculty
Fachbereich Biologie
Publisher
Philipps-Universität Marburg
Language
eng
Data types
DoctoralThesis
Keywords
Directed EvolutionPhotosynthesisCarbonBiochemistryfixationCO2PhotorespirationMetabolismSynthetic
DFG-subjects
PhotosyntheseEnzyme EngineeringCO2-Fixierung
DDC-Numbers
570
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Marchal, Daniel Guy Henri (0009-0002-1314-4583): Exploring and engineering enzymes for new-to-nature photorespiration. : Philipps-Universität Marburg 2025-08-06. DOI: https://doi.org/10.17192/z2024.0244.
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Except where otherwised noted, this item's license is described as Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 - CC BY NC ND