SAFETY ASSESSMENT OF GENETICALLY-ENGINEERED YEAST - ELIMINATION OF MUTAGENICITY OF THE YEAST SACCHAROMYCES-CEREVISIAE BY DECREASING THE ACTIVITY OF METHYLGLYOXAL SYNTHASE

Methylglyoxal synthase catalyses the transformation of dihydroxyaceton ephosphate to methylglyoxal, a toxic 2-oxoaldehyde which is found to b e present in the yeast Saccharomyces cerevisiae DKD-5D-H. Yeast cells in which genes for phosphoglucose isomerase, phosphofructokinase and t riosephosphate isomerase had been extrachromosomally amplified by usin g a multi-copy plasmid showed an increased ability to induce mutagenes is in standard tests when compared to wild type yeast. This response i s mainly due to the increased amount of methylglyoxal in the engineere d cells. To decrease the mutagenic activity and make it possible to us e genetically engineered yeasts for practical fermentation processes, a mutant having a decreased level of methylglyoxal synthase activity w as isolated. When transformed with genes for the glycolytic enzymes, t he mutant cells showed extremely low levels of methylglyoxal content a nd mutagenic activity, both levels being comparable with those of non- transformed DKD-5D-H cells.