ENHANCED PRODUCTIVITY THROUGH GRATUITOUS INDUCTION IN RECOMBINANT YEAST FERMENTATIONS

The advantages of gratuitous induction for GAL-regulated cloned gene ( lacZ) product synthesis were evaluated for the yeast Saccharomyces cer evisiae. The growth yield, and productivity of a gratuitous (gal1) str ain were compared with those of an otherwise isogenic, nongratuitous ( GAL1) strain. Batch studies clearly demonstrated the improvements poss ible in product synthesis when the inducer is not metabolized by the y east cells; both beta-galactosidase specific and volumetric activities were superior for the gal1 strain. At equivalent metabolizable sugar concentrations, the productivity of the gratuitous strain exceeded tha t of the nongratuitous strain by 180 %. The effects of initial inducer concentration and induction time were also examined. For the gratuito us strain, galactose glucose ratios as low as 0.1 still gave maximum b eta-galactosidase volumetric activity. A 5-fold higher ratio was neces sary for full induction with the nongratuitous strain, and productivit y was substantially lower relative to the gal1 strain. A comparison of various times for galactose addition indicated that productivity is h ighest when the gratuitous culture is induced for the entire batch fer mentation.