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.