High-cell-density fermentation of recombinant Saccharomyces cerevisiae using glycerol

To obtain a high cell density of recombinant Saccharomyces cerevisiae (INVSc 1 strain bearing a 2 mum plasmid, pYES2 containing a GAL1 promoter for expression of the beta-galactosidase gene), the yeast was grown with glycerol as the substrate by fed-batch fermentation. The feeding strategy was based on an on-line response of the medium pH to the consumption of glycerol. The approach was to feed excess carbon into the medium to create a benign environment for rapid biomass buildup. During cell growth in the presence of glycerol, the release of protons in the medium caused a decrease in pH and the consumption rate of ammonium phosphate served as an on-line indicator for the metabolic rate of the organism. The extent of glycerol feeding in a fed-batch mode with pH control at 5.0 +/- 0.1 was ascertained from the automatic addition of ammonium phosphate to the medium. The glycerol feeding to ammonium phosphate addition ratio was found to be 2.5-3.0. On the basis of the experiments, a maximum dry cell biomass of 140 g per liter and a productivity of 5.5 g DCW/L/h were achieved. The high cell density of S. cerevisiae obtained with good plasmid stability suggested a simple and efficient fermentation protocol for recombinant protein production.