Sugar Synthesis from CO2 in Escherichia coli

Area of Science:

• Synthetic biology
• Metabolic engineering
• Microbial biotechnology

Background:

• Heterotrophic organisms typically cannot synthesize biomass directly from carbon dioxide (CO2).
• Establishing non-native carbon fixation pathways in microbes remains a significant challenge.
• The Calvin-Benson-Bassham (CBB) cycle is a primary mechanism for CO2 assimilation in autotrophs.

Purpose of the Study:

• To engineer a heterotrophic organism, E. coli, to synthesize biomass precursors from CO2.
• To investigate the feasibility of implementing a non-native CBB cycle for carbon fixation.
• To explore the potential for trophic-mode evolution in microbial metabolism.

Main Methods:

• Rational metabolic rewiring of E. coli.
• Recombinant expression of a non-native CBB cycle.
• Laboratory evolution of engineered E. coli strains.
• Genome sequencing to identify key mutations.

Main Results:

• Successfully established a functional non-native CBB cycle in E. coli.
• Engineered bacteria synthesized sugars and other biomass constituents from CO2.
• Carbon fixation was coupled to the oxidation of an organic compound (e.g., pyruvate) for energy and reducing power.
• Mutations in flux branchpoints were identified as crucial for the observed phenotype.

Conclusions:

• Demonstrated the successful evolution of a non-native carbon fixation pathway in a heterotrophic bacterium.
• Highlighted the potential for rapid trophic-mode evolution of microbial metabolism.
• Showcased a significant step towards engineering microbes for direct CO2 utilization in biotechnology.
• While net carbon gain was not achieved, the study provides a foundation for future advancements.