Safety assessment of genetically engineered yeast and breeding of non-toxigenic industrially used yeasts

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The safety of genetically engineered yeast cells was assessed by determining the change in cellular level of methylglyoxal (MG), a typical toxic ketoaldehyde biosynthesized from dihydroxyacetonephosphate by an action of methylglyoxal synthase (MGS). The following results were obtained. (1) when the cells of Saccharomyces cerevisiae transformed with glycolytic enzyme genes (phosphoglucose isomerase, phosphofructokinase and triosephosphate isomerase genes) were incubated in fermentation conditions with large amount of glucose, MG was accumulated in cells at a mutagenic level. (2) The enzymatic study indicated that MGS was entirely responsiblefor the observed accumulation of MG.(3) The deficiency of MGS dramatically lowered the cellular MG level. From these results, the inspection of MG fluctuation in genetically engineered yeast cells is necessary for the safety utilization of the created yeast in practical fermenta-tion processes.The physiological function of MGS was also studied in rel … More ation to the yeast sporulation. The activity of the enzyme was closely related to the sporulation capability of Sake yeasts. The finding was applied to the Sake yeast cells that show no sporulation capability. The removal of MG resulted in the marked increase in sporulation efficiency of Sake yeast and provided means for molecular breeding by hybridization. We were awarded a "Eda prize" from Japan Society of Fermentation and Bioengineering in 1995.The safety assessment was extended to the genetically transformed potato with soybean glycinin gene. The expression level of glycinin was about 1% of the total potato protein. The levels of lipid, carbohydrate, ash, fiber, vitamin, and fatty acids were almost the same as those of control (transformed potato with a vector or non-transformed natural potato). However, transformed potato with a vector or the vector habouring giycinin gene showed increased level of glycoalkaroids (solanin and chakonin) and the level reached 1.5-2 fold of the control. The results indicated that the suitable combination of vector and plant to be transformed is important in creation transgenic plant and/or genetically engineered foods. Less