Enhanced citric acid production by a yeast Yarrowia lipolytica over-expressing a pyruvate carboxylase gene.

In this study, after the expression of a pyruvate carboxylase gene (PYC) cloned from Meyerozyma guilliermondii in a marine-derived yeast Yarrowia lipolytica SWJ-1b, a transformant PG86 obtained had much higher PYC activity than Y. lipolytica SWJ-1b. At the same time, the PYC gene expression and citric acid (CA) production by the transformant PG86 were also greatly enhanced. When glucose concentration in the medium was 60.0 g L(-1), CA concentration formed by the transformant PG86 was 34.02 g L(-1), leading to a CA yield of 0.57 g g(-1) of glucose. During a 10-L fed-batch fermentation, the final concentration of CA was 101.0 ± 1.3 g L(-1), the yield was 0.89 g g(-1) of glucose, the productivity was 0.42 g L(-1) h(-1) and only 5.93 g L(-1) reducing sugar was left in the fermented medium within 240 h of the fed-batch fermentation. HPLC analysis showed that most of the fermentation products were CA.