Innovative metabolic pathway design for efficient l-glutamate production by suppressing CO2 emission.

In the pathway of L-glutamic acid (L-Glu) biosynthesis in Corynebacterium glutamicum, 1 mol of L-Glu is synthesized from 1 mol of glucose at a cost of 1 mol of carbon dioxide (CO(2)), with a maximum theoretical yield of 81.7% by weight. We have designed an innovative pathway for efficient L-Glu production employing phosphoketolase (PKT) to bypass the CO(2)-releasing pyruvate dehydrogenase reaction, thereby increasing the maximum theoretical yield of L-Glu from glucose to up to 98.0% by weight (120% mol/mol L-Glu produced/glucose consumed). The xfp gene encoding PKT was cloned from Bifidobacterium animalis and overexpressed under the strong cspB promoter in C. glutamicum. A functional enzyme was detected in an L-Glu-producing strain of C. glutamicum (odhA). When cells of this producer strain with the xfp gene and those without the xfp gene were cultivated in a controlled fermentation system, the L-Glu production yield of the strain expressing the xfp gene was much higher than that of the original strain, coupled with the suppression of CO(2) emission. Consequently, we could successfully enhance L-glutamate production by installing the PKT pathway of B. animalis into C. glutamicuml-Glu metabolism, and this novel metabolic design will be able to increase L-Glu production yield beyond the maximum theoretical yield obtained from the conventional metabolic pathway of biosynthesis from glucose.