Calado_2003_J.Biosci.Bioeng_96_141

Saccharomyces cerevisiae SU50 strain was cultivated with different concentrations of glucose and galactose with the aim of increasing cutinase activity, cutinase yield on the carbon source, and bioreactor productivity. Cultivations in shake flasks with galactose as the sole carbon source, with sugar concentrations between 10 and 40 g/l, exhibited growth-associated cutinase production and a constant specificity of cutinase secretion. Furthermore, as the galactose concentration increased to values higher than 15 g/l, a progressively higher maximum specific galactose consumption rate and a consequent higher alcoholic fermentation occurred, resulting in progressively lower biomass yields on the carbon source and cutinase yields on biomass. Using high glucose and galactose concentrations in a well-aerated bioreactor resulted in a high biomass productivity (0.5 g dcw/l/h), a high cutinase yield on biomass (21.5 U/mg dew), a final high cutinase secretion efficiency (97%), and plasmid stability (99%). Based on these studies, a two phase fed-batch cultivation strategy was developed. A batch phase with high glucose and galactose concentrations, followed by a fed-batch with a constant feed rate with galactose as the sole carbon source in order to minimize the repression of the GAL 7 promoter, were established. The feed rate was estimated to maintain a pre-determined concentration of galactose (20 g/l) on the culture medium in order to maximize the efficiency of cutinase secretion and minimize the galactose alcoholic fermentation. By this cultivation strategy, enhancements of 3.6-fold in cutinase activity, 1.2-fold in cutinase yield on the carbon source, and 8.7-fold culture productivity were obtained in relation to a batch cultivation performed in shake flasks with 20 g/l of galactose.