Metabolic engineering of Corynebacterium glutamicum for glycolate production

Corynebacterium glutamicum - a well-known industrial amino acid producer - has recently been engineered for the production of a variety of new products including diamines, alcohols, carotenoids and organic acids. Glycolic acid was shown here not to serve as sole or combined carbon source for C. glutamicum. Glycolate affected growth of C. glutamicum only at high concentrations (460 mM) and in a comparable manner as other salts (480 mM potassium chloride and 490 mM sodium chloride). A transcriptome analysis of cells grown in the presence of glycolate or potassium chloride revealed nine glycolate-specific gene expression changes including increased levels of a putative l-lactate permease gene when glycolate was present in medium. Subsequently, glycolate was shown to interfere with l-lactate utilization but not with growth with acetate or pyruvate. Heterologous expression of the glyoxylate reductase gene ycdW from Escherchia coli resulted in a titer of 0.4 g/L glycolate in minimal medium with glucose and acetate. Deletion of the malate synthase gene aceB improved glycolate titer by about tenfold. Reducing isocitrate dehydrogenase activity by replacing the translational start codon (ATG to GTG) further increased glycolate titer by more than 30%. The production of 5.3 ± 0.1 g/L glycolate with a yield of 0.18 g/g and a volumetric productivity of about 0.1 g L−1 h−1 is the first report of a C. glutamicum strain capable of glycolate production.