Lactose utilization by Saccharomyces cerevisiae strains expressing Kluyveromyces lactis LAC genes

Whey generated in cheese manufacture continues being an industrial problem without a satisfactory solution. Genetic modification of the yeast S. cerev isiae to obtain strains able to utilize lactose, is a prerequisite for the utilization of this yeast to convert cheese whey into useful fermentation p roducts (i.e. biomass, heterologous protein and other recombinant products) . Although the construction of S. cerevisiae Lac(+) strains has been achiev ed by different strategies, most of these strains have unsuitable character istics, such as genetic instability of the Lac phenotype or diauxic growth. In previous communications we have described the construction of genetical ly stable strains of S. cerevisiae that assimilate lactose with a high effi ciency. These strains carry multiple copies of Kluyveromyces lactis LAC4 an d LAC12 genes, which code for a beta -galactosidase and a lactose permease, respectively. In this work we report additional results about the effect o f gene dosage, and analyze the performance of a selected strain in the bioc onversion of cheese whey. Additionally, we describe the construction of a n ew strain, which combines the Lac(+) phenotype with additional properties o f biotechnological interest: flocculence, and the ability to hydrolyze star ch. (C) 2000 Elsevier Science B.V. All rights reserved.