FIG. 5.

Example of a high-cell-density culture of transformed S. cerevisiae yeast cells converting l-galactose to l-ascorbic acid (values expressed as milligrams per liter per optical density). S. cerevisiae GRF18U wt or GRF18U transformed with ALO1 or LGDH and ALO1 was pregrown overnight on mineral medium (2% [wt/vol] glucose and 0.67% [wt/vol] YNB), starting with an OD₆₆₀ of 0.05. At time zero, the cells were concentrated 10 times, and 250 mg of l-galactose liter⁻¹ was added. The cultures were kept under standard conditions for 6 days. At the indicated times, samples were taken, and the l-ascorbic acid concentration in the culture broth was determined. While the wt (□) cells did not accumulate l-ascorbic acid in the culture medium, cells transformed with ALO1 alone (•) or ALO1 and LGDH (○) secreted considerable amounts of vitamin C.