Overexpression of the ICL1 gene changes the product ratio of citric acid production by Yarrowia lipolytica.

The yeast Yarrowia lipolytica secretes high amounts of various organic acids, like citric (CA) and isocitric (ICA) acids, triggered by growth limitation caused by different factors and an excess of carbon source. Depending on the carbon source used, Y. lipolytica strains produce a mixture of CA and ICA in a characteristic ratio. To examine whether the CA/ICA product ratio can be influenced by gene-dose-dependent overexpression or by disruption of the isocitrate lyase (ICL)-encoding gene ICL1, recombinant Y. lipolytica strains were constructed, which harbour multiple ICL1 copies or a defective icl1 allele. The high-level expression of ICL in ICL1 multicopy integrative transformants resulted in a strong shift of the CA/ICA ratio into direction of CA. On glycerol, glucose and sucrose, the ICA proportion decreased from 10-12% to 3-6%, on sunflower oil or hexadecane even from 37-45% to 4-7% without influencing the total amount of acids (CA and ICA) produced. In contrast, the loss of ICL activity in icl1-defective strains resulted in a moderate 2-5% increase in the ICA proportion compared to ICL wild-type strains on glucose or glycerol.