Genetic engineering in the improvement of brewers yeast.

Von Wettstein, D., Gjermansen, C., Holmberg, S., Kielland-Brandt, M.C., Nillson-Tillgren, T., Pedersen, M.B., Litske, J.G. and Sigsgaard, P.

Abstract
Available tools in genetic engineering are outlined. Their use in the handling and improvement of brewers yeast are described with the following examples: (1) single chromosome transfer has allowed the genetic mapping and molecular characterization of genes in chromosomes III, V, XII and XIII of the Carlsberg lager production strain; (2) DNA- DNA hybridization with radioactively labelled plasmids containing genes for ribosomal RNA or histidine biosynthesis (HIS 4) is used to distinguish lager strains, ale strains, wine yeasts and wild yeasts in research as well as microbiological control; (3) a leucine requiring mutant has been induced in a meiotic segregant of the Carlsberg lager production strain and genetically transformed with a yeast E. coli shuttle vector carrying a LEU2 cerevisiae gene. This gene can remedy the leucine requirement of the mutant; (4) more than 200 hybrid strains from crosses among meiotic segregants of 2 distinct lager brewing strains have been produced. Of these, 34 have been tested in 2-1 pilot fermentations and 9 strains were found to have normal or improved fermentation performance. 1 hybrid strain has been successfully tested in 600 hl scale; (5) 4 genes catalyzing steps in the biosynthesis of iso leucine and valine have been mapped on their respective chromosomes. Genes ILV1 and ILV2 have been cloned in yeast E. coli shuttle vectors and partial nucleotide sequences established for the threonine deaminase gene (ILV1). Prospects for the construction of strains with limited production of acetolactate are outlined.
Keywords: brewers' yeast chromosome deoxyribonucleic acid genetic mapping genetics hybridisation survey transformation