LACTOSE WHEY UTILIZATION AND ETHANOL-PRODUCTION BY TRANSFORMED SACCHAROMYCES-CEREVISIAE CELLS

Strains of Saccharomyces cerevisiae transformed with a multicopy expression vector bearing both the Escherichia coli β‐galactosidase gene under the control of the upstream activating sequence of the GAL1–10 genes and the GAL4 activator gene release part of β‐galactosidase in the growth medium. This release is due to cell lysis of the older mother cells; the enzyme maintains its activity in buffered growth media. Fermentation studies with transformed yeast strains showed that the release of β‐galactosidase allowed an efficient growth on buffered media containing lactose as carbon source as well as on whey‐based media. The transformed strains utilized up to 95% of the lactose and a high growth yield was obtained in rich media. High productions of ethanol were also observed in stationary phase after growth in lactose minimal media. Copyright © 1992 John Wiley & Sons, Inc.