Manipulation of Carbon flux in S. cerevisiae to improve L-lactic acid production
双层面调控S. cerevisiae碳流促进L-乳酸积累

Abstract: Objective] The target of this study was to develop an engineered Sacchromyces cerevisiae strain to produce L-lactic acid efficiently using glucose as carbon source. Methods] For construction of the strain CEN.PK2-1CLDH], we integrated a LDH gene coding L-lactic acid dehydrogenase from Bovine into the genome of S. cerevisiae via homologous recombination and meanwhile knocked out a PDC1 gene coding pyruvate decarboxylase. As this, the carbon fluxes were led into L-Lactic acid. On the basis, we analyzed the Km value of these key enzymes to NADH and successfully over-expressed a NADH oxidase (nox) from Streptococcus pneumoniae into the cytoplasm for the construction of S. cerevisiae CEN.PK2-1CLDH]-nox. Results] Compared to initial strain, the yield of L-lactic acid in CEN.PK2-1CLDH] fermentation liquor increased from 0 g/L to 15 g/L and the concentration of ethanol decreased from 27.3 g/L to 16.2 g/L. Furthermore, the concentration of L-lactic acid increased further to 20 g/L and the concentration of ethanol decreased to 8.2 g/L. Conclusions] The results indicated that carbon metabolic flux was redistributed to efficient accumulation of L-lactic acid through two-sided control that heterologous expression of the gene LDH and decreasing the ratio of NADH/NAD+.