Multicriteria evaluation of ethylene glycol assimilation pathways

Biomanufacturing can play a pivotal role in the transition away from fossil fuel dependence for the production of chemicals and fuels. There is growing interest in inexpensive alternative bioproduction feedstocks from renewable sources that avoid competing with food production for land use. Ethylene glycol (EG), a C2 compound that can be recovered from plastic waste or derived from carbon dioxide, is gaining attention as a carbon source for microbial processes. Here, we systematically evaluate natural and synthetic metabolic pathways for EG assimilation using theoretical modeling approaches. We analyzed five pathways for their maximum theoretical yields, thermodynamic favourability, enzyme costs, and orthogonality to cell growth and identify favourable traits for each of these pathways for a given product. Our results reveal distinct trade-offs between pathway types. Synthetic pathways achieved higher theoretical yields for biomass and most bioproducts, with synthetic glycolaldehyde assimilation (SAGA) pathways showing the best overall yields and the synthetic acetyl-CoA assimilation (SACA) pathway demonstrating the highest thermodynamic favourability and lowest enzyme costs. Among natural pathways, the glycerate pathway exhibited favourable thermodynamics and moderate enzyme costs comparable to synthetic alternatives, while being particularly advantageous for glycolate production despite carbon losses. The β-hydroxyaspartate cycle (BHAC) showed the poorest thermodynamic performance and highest enzyme burden. However, natural pathways exhibited equal or higher orthogonality to growth-associated reactions, making them potentially suitable for dynamically controlled production systems. These findings provide guidance for selecting optimal EG assimilation strategies based on target products and process requirements, supporting the development of sustainable bioprocesses utilizing this promising unconventional feedstock. One-sentence summary This article reviews and compares metabolic pathways for the utilization of the compound EG in the context of bioproduction.