Abstract
Microbial fermentations might be limited by rate-limiting steps in biosynthesis processes. The lactic acid production in Lactobacillus plantarum could be limited by the rate of glycolytic flux. We examined by formation of alternativepathway of conversion of phosphoenolpyruvate to pyruvate in L. plantarum NCIMB 8826. The tricarboxylic acid (TCA) cycle intermediate malate can be conversion to pyruvate by malic enzyme (ME) in this strain. We investigated the increase that metabolic flux from glycolysis to the reductive TCA cycle by overexpression of the phosphoenolpyruvate carboxykinase (PEPCK) in this strain. The role of ME in the alternative pathway was assessed by the ME deficient strain.The PEPCK-overexpressing strain yielded more succinic acid than the control strain after 24 hours of fermentation.These results showed that the PEPCK-overexpressing strain increased the metabolic flux from glycolysis to the reductive TCA cycle. The succinic acid production of the PEPCK-overexpressing ME deficient strain was higher than that of the PEPCK-overexpressing strain. It is suggested that the PEPCK-overexpressing strain converted malate to pyruvate.Since the PEPCK-overexpressing strain increased the cell yield, these data suggested that overexpression of PEPCK in this strain can be a useful technique for effective fermentative production.
