INDUSTRIAL YEAST-STRAIN IMPROVEMENT - CONSTRUCTION OF A HIGHLY FLOCCULANT YEAST WITH A KILLER CHARACTER BY PROTOPLAST FUSION

Conditions were optimized for rapid release and improved regeneration of protoplasts of saccharomyces cerevisiae NCIM 3458. Rapid protoplast release was also obtained with representatives of several other yeast genera under the modified conditions of treatment. The application of the procedure in construction of a highly flocculent saccharomyces ce revisiae with a killer character is described. Fusion was effected bet ween UV-killed protoplasts of S. cerevisiae NCIM 3578 with a killer ch aracter and live protoplasts of the highly flocculent S. cerevisiae NC IM 3528 in the presence of polyethylene glycol (PEG) 6000. Fusants wer e selected using benomyl resistance as marker, the killer toxin produc er rather than the highly flocculent yeast being resistant to the fung icide at a concentration of 100 mu g ml(-1). Fusants were also charact erized by their DNA contents, capacity for ethanolic fermentation of m olasses sugar and levels of invertase, alcohol dehydrogenase and pyruv ate decarboxylase activities.