Semi-industrial scale (30 m3) fed-batch fermentation for the production of D-lactate by Escherichia coli strain HBUT-D15.

D(-)-lactic acid is needed for manufacturing of stereo-complex poly-lactic acid polymer. Large scale D-lactic acid fermentation, however, has yet to be demonstrated. A genetically engineered Escherichia coli strain, HBUT-D, was adaptively evolved in a 15% calcium lactate medium for improved lactate tolerance. The resulting strain, HBUT-D15, was tested at a lab scale (7 L) by fed-batch fermentation with up to 200 g L-1 of glucose, producing 184-191 g L-1 of D-lactic acid, with a volumetric productivity of 4.38 g L-1 h-1, a yield of 92%, and an optical purity of 99.9%. The HBUT-D15 was then evaluated at a semi-industrial scale (30 m3) via fed-batch fermentation with up to 160 g L-1 of glucose, producing 146-150 g L-1 of D-lactic acid, with a volumetric productivity of 3.95-4.29 g L-1 h-1, a yield of 91-94%, and an optical purity of 99.8%. These results are comparable to that of current industrial scale L(+)-lactic acid fermentation.