Expression of pyruvate carboxylase enhances succinate production in Escherichia coli without affecting glucose uptake

Plasmids carrying the pyc gene from Rhizobium etli were used to express pyruvate carboxylase in Escherichia coli. Results of batch fermentations of a wild-type E. coli (MG1655), this wild-type with the pUC18 cloning/expression vector (MG1655/pUC18) and this wild-type carrying the pyc gene (MG1655/pUC18-pyc) were compared in glucose-limited medium. The results indicate that the final succinate concentration upon complete glucose utilization was increased from 1.18 g/L to 1.77 g/L by the expression of pyc, while the final succinate concentration in MG1655/pUC18 was slightly lower than in the parent strain. This increased succinate concentration came at the expense of lactate synthesis, whose final concentration decreased from 2.33 g/L to 1.88 g/L. The expression of pyc did not affect the maximum glucose uptake (2.17 g/L.h for MG1655 versus 2.47 g/L.h for MG1655/pUC18-pyc), but did decrease the maximum rate of cell mass production (0.213 g/L.h for MG1655, 0.169 g/L.h for MG1655/pUC18 and 0.199 g/L.h for MG1655/pUC18-pyc).