Sugar synthesis from CO2 in E. coli

Can a heterotrophic organism be evolved to synthesize biomass directly from CO2? So far, non-­native carbon fixation, where 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 (i.e. pyruvate). Genome sequencing reveals that mutations in flux branch points, 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.