Abstract:The mutant of Saccharomyces cerevisiae XM2-9 has been used for the production of Se-methylselenocysteine by fed-batch fermentation. First, the optimal medium and sulfur concentration were obtained by batch fermentation. The specific growth rate of cell at different initial disodium selenite concentrations was calculated. Meanwhile, the specific selenium consumption rate (SSCR) was calculated under different concentrations of magnesium sulfate, and the highest SSCR of 0.47 mg/(g·h) was achieved. Afterward, Se-methylselenocysteine production was carried out using a fed-batch fermentation mode. At first, the glucose medium was used as the feeding material. Then three flow rates were selected to carry out the constant flow test according to the calculation of the specific growth rate of the yeast cell. Simultaneously, the flow rate of disodium selenite solution was controlled via SSCR. The highest organic selenium productivity of 10.16 mg/(L·h) was achieved when the flow rate of glucose medium was 0.8 L/h. It was found that the exponential flow mode was better than the constant speed flow mode based on the study on glucose flow. The experimental results showed that the exponential flow rate set at μ=0.08 h-1 resulted in a maximum production intensity of organic selenium, which reached 12.55 mg/(L·h). Under the optimized conditions, the final concentration of yeast cell was 35.6 g/L, and the organic selenium content in the cell was 4 937 μg/g. Among them, 72% of total selenium compounds were in the form of Se-methylselenocystein (3 555 μg/g). The final concentration of Se-methylselenocystein reached 8 189 μg/g based on the molecular weight conversion.
