Metabolic Engineering of Lactococcus lactis for the Enhanced Production of Lactate by Manipulating Pyruvate Dehydrogenase Complex E2 and Lactate Dehydrogenase.

Abstract

The pyruvate dehydrogenase complex (PDHc) in Lactococcus lactis, composed of pdh E1α, E1β, and E2, links glycolysis to the tricarboxylic acid cycle (TCA cycle). This study investigated the effect of the pdh E2 knockout on metabolism. The knockout strain showed 76% biomass, 48% lower PDHc activity, and 13.4% reduced ATP versus wild type but a 1.5-fold higher NAD+/NADH ratio. Lactate production increased by 5.6% in the knockout and 45.3% in overexpressing strains. Next to this, the lactate dehydrogenase activity was induced, achieving the highest enzyme amount with the addition of 5 ng/mL nisin after 48 h of induction (28.7% higher than that of wild-type L. lactis). In addition, the transcript levels of genes related to the pyruvate metabolic pathway also changed: pdh E2 decreased by 67.62%, while pdh E1β was upregulated 15-fold. Our study provides insights for enhancing lactate production and understanding pdh E2 function.