Sugar Synthesis from CO2 in Escherichia coli

Can a heterotrophic organism be evolved to synthesize biomass from CO2 directly? So far, non-native carbon fixation in which biomass precursors are synthesized solely from CO2 has remained an elusive grand challenge. Here, we demonstrate how a combination of rational metabolic rewiring, recombinant expression, and laboratory evolution has led to the biosynthesis of sugars and other major biomass constituents by a fully functional Calvin-Benson-Bassham (CBB) cycle in E. coli. In the evolved bacteria, carbon fixation is performed via a non-native CBB cycle, while reducing power and energy are obtained by oxidizing a supplied organic compound (e.g., pyruvate). Genome sequencing reveals that mutations in flux branchpoints, connecting the non-native CBB cycle to biosynthetic pathways, are essential for this phenotype. The successful evolution of a non-native carbon fixation pathway, though not yet resulting in net carbon gain, strikingly demonstrates the capacity for rapid trophic-mode evolution of metabolism applicable to biotechnology. [Display omitted] [Display omitted] •Non-native Calvin-Benson cycle allows for sugar synthesis from CO2 in E. coli•Metabolic cutoff allows for the decoupling of energy harvesting from biomass synthesis•Chemostat-based directed evolution led to the emergence of sugar synthesis from CO2•Mutations in flux branchpoints are essential for the CBB cycle stable operation Metabolic rewiring and directed evolution lead to a fully functional, non-native carbon fixation cycle, which synthesizes sugars and other major biomass components in E. coli.