Construction of a Synthetic Metabolic Pathway for the Carbon-Conserving Biosynthesis of Value-Added Products from Ethylene Glycol and Glycolaldehyde

• Applicant: Professor Dr.-Ing. Thomas Walther
• Subject Area: Biological Process Engineering
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413016763

Development of the bio-based economy requires the exploitation of new carbon sources to satisfy the increasing demand for organic substrates that can be used in microbial product syntheses. The most sustainable strategy to meet this demand is to use carbon dioxide (CO2) as renewable carbon source for production of chemical compounds. To make CO2 accessible as a substrate for heterotrophic microorganisms, it is first chemically converted to methanol or synthesis gas. Both compounds are attractive carbon sources from which the whole panel of industrially relevant chemicals can be produced by microorganisms. However, the performance of these microbial product syntheses is limited by the extremely high oxygen demand of methanol-based biosyntheses and comparatively slow phase transition of the gaseous substrates synthesis gas and oxygen into the liquid culture medium. To solve these technological problems, the Institute of Natural Materials Technology of the Technische Universität Dresden proposes to chemically convert synthesis gas and methanol into the liquid and non-volatile C2-compounds ethylene glycol (EG) and glycolaldehyde (GA). Using these liquid compounds as carbon sources solves the phase transition problem. In addition, conversion of these molecules into value-added products (by the herein proposed synthetic metabolic pathways) has a significantly lower oxygen demand than when directly using methanol as the substrate.Various bacteria are capable of using EG and GA as a carbon source. However, natural EG-assimilating pathways contain several CO2-releasing reactions, which makes them particularly unsuitable for acetyl-CoA dependent product syntheses (maximum carbon yield of acetyl-CoA on EG is 50 %). In this research project, a synthetic metabolic pathway is proposed which enables carbon-conserving biosynthesis of acetyl-CoA from EG. The pathway relies on the initial oxidation of EG to GA and the aldol addition of GA to glyceraldehyde 3-phosphate (GAP). The reaction product arabinose 5-phosphate is further processed by several reaction steps to yield acetyl-CoA and to regenerate the GA-acceptor GAP. The function of the synthetic pathway will be first demonstrated in a cell-free reaction system by using isolated enzymes. This work is followed by implementation of the pathway in an engineered Escherichia coli strain. In vivo function of the pathway will be demonstrated by showing biosynthesis of mevalonate which is derived from acetyl-CoA. Optimization of EG-assimilation and mevalonate production will be guided by systems level physiological analyses.Our study makes an important contribution to the exploitation of alternative carbon sources for microbial product syntheses.

• DFG Programme: Research Grants