Metabolic engineering of E. coli for efficient production of glycolic acid from glucose

Glycolic acid is the smallest member of the α-hydroxy acid family. In order to produce glycolate from glucose via the glyoxylate shunt stably, one malate synthase gene aceB in Escherichia coli BW25113 was deleted by homologous recombination; another malate synthase gene glcB was then replaced by a DNA cassette WAK harboring isocitrate lyase gene (aceA), glyoxylate reductase gene (ycdW) and isocitrate dehydrogenase kinase/phosphatase gene (aceK). The above three genes were over-expressed in the chromosome of E. coli EYX-1WAK. This strain was then transferred 20 times on M9 medium to have a mutant strain: EYX-2 with a significantly improved growth rate. The glycolate yields of EYX-2 in the shaken flasks and the 5-L bioreactor using batch fermentation strategy under 2 vvm aeration and 800 rpm stirring speed were 0.33 g/g-glucose and 0.48 g/g-glucose, respectively. The fed-batch fermentation of EYX-2 on 120 g/L glucose had the highest titer of 56.44 g/L with 0.52 g/g-glucose yield in 120 h, and this is the highest reported glycolate yield ever.