OBJECTIVE: We developed an engineered Sacchromyces cerevisiae strain to produce L-lactic acid efficiently by using glucose as carbon source. METHODS: For construction of the strain CEN. PK2-1C [LDH], we integrated an 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. The carbon fluxes were led into L-Lactic acid. We analyzed the Km value of these key enzymes to NADH and over-expressed an NADH oxidase (nox) from Streptococcus pneumoniae into the cytoplasm for the construction of S. cerevisiae CEN. PK2-1C [LDH] -nox. RESULTS: Compared to the initial strain, the yield of L-lactic acid in CEN. PK2-1C [LDH] fermentation broth 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. Compared to CEN. PK2-1C [LDH], the yield of L-lactic acid in CEN. PK2-1C [LDH] -nox fermentation broth increased from 15 g/L to 20 g/L and the concentration of ethanol decreased from 16.2 g/L to 8.2 g/L. CONCLUSIONS: The 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+.
OBJECTIVE: We developed an engineered Sacchromyces cerevisiae strain to produce L-lactic acid efficiently by using glucose as carbon source. METHODS: For construction of the strain CEN. PK2-1C [LDH], we integrated an 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. The carbon fluxes were led into L-Lactic acid. We analyzed the Km value of these key enzymes to NADH and over-expressed an NADH oxidase (nox) from Streptococcus pneumoniae into the cytoplasm for the construction of S. cerevisiaeCEN. PK2-1C [LDH] -nox. RESULTS: Compared to the initial strain, the yield of L-lactic acid in CEN. PK2-1C [LDH] fermentation broth 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. Compared to CEN. PK2-1C [LDH], the yield of L-lactic acid in CEN. PK2-1C [LDH] -nox fermentation broth increased from 15 g/L to 20 g/L and the concentration of ethanol decreased from 16.2 g/L to 8.2 g/L. CONCLUSIONS: The 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+.