Enhanced glycolic acid yield through xylose and cellobiose utilization by metabolically engineered Escherichia coli

Microbial biorefinery is a promising route toward sustainable production of glycolic acid (GA), a valuable raw material for various industries. However, inherent microbial GA production has limited substrate consumption using either d-xylose or d-glucose as carbon catabolite repression (CCR) averts their co-utilization. To bypass CCR, a GA-producing strain using d-xylose via Dahms pathway was engineered to allow cellobiose uptake. Unlike glucose, cellobiose was assimilated and intracellularly degraded without repressing d-xylose uptake. The final GA-producing E. coli strain (CLGA8) has an overexpressed cellobiose phosphorylase (cep94A) from Saccharophagus degradans 2-40 and an activated glyoxylate shunt pathway. Expression of cep94A improved GA production reaching the maximum theoretical yield (0.51 g GA g(-1) xylose), whereas activation of glyoxylate shunt pathway enabled GA production from cellobiose, which further increased the GA titer (2.25 g GA L-1). To date, this is the highest reported GA yield from d-xylose through Dahms pathway in an engineered E. coli with cellobiose as co-substrate.

Automated summary

A modified microbial strain capable of producing glycolic acid from d-xylose was engineered to utilize cellobiose as a co-substrate, resulting in improved glycolic acid production with high yield.