Toward Low-Carbon-Footprint Glycolic Acid Production for Bioplastics through Metabolic Engineering in Escherichia coli

Researchers are focusing on biological carbon dioxide abatement against the currently employed physical and chemical methods. Sustainable approaches for carbon conversion into indispensable bulk chemicals are the need of the hour. In this study, glycolic acid (GA), one of the promising components for bioplastics, food, and pharmaceutical industries, was produced in a low-carbon footprint manner using genetically engineeredEscherichia coli for the first time. By fine-tuning the genes in the TCA cycle and glyoxylate shunt, GA yield reached 0.21 g/g-glucose with a productivity of 0.08 g/L/h. Regeneration of NADPH was improved using glyceraldehyde-3-phosphate dehydrogenase (gapC) fromClostridium acetobutylicum in the glucose-6-phosphate-1-dehydrogenase (zwf) mutant. To further enhance CO2 uptake and carbon flux into the TCA cycle, phosphoenolpyruvate carboxylase (ppc) and pyruvate carboxylase (pyc) were applied. As a result, the titer and productivity of GA reached 11.9 g/L and 0.23 g/L/h, respectively, with a 41% reduction in CO2 emission compared to the strain without ppc expression during fermentation. Finally, GA was polymerized to form poly(glycolic acid) and characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The presented strategy serves as an eco-friendly and cost-efficient approach for chemical production toward low-carbon emission.