Yeast selection for high resistance to and uptake of Se: Cultural optimization of organic selenium production

Se-rich yeast within animal feeds is much more effective than additions of inorganic Se in increasing the concentration of Se in eggs, milk and meat. This study was conducted in order to select mutant Saccharomyces cerevisiae which produce higher levels of organic selenium (Se) and to improve the productivity of this Se-rich yeast by optimization of the culturing condition. Among 13 ATCC strains of S. cerevisiae, ATCC 560 showed a higher tolerance towards Se, exhibiting a total Se uptake rate of 6.69 mg/l. The mutant S. cerevisiae 6M, which is an ATCC 560 derivative developed through UV mutagenesis, showed about 20% increased Se production rates (8.0 mg/l). Optimal culturing conditions were determined, in terms of the timing and addition of inorganic Se, initial pH, and overall culturing time. The optimal concentration of inorganic Se was determined to be 125 ppm, the optimum time for the addition of which was determined to be at the start of incubation. The optimal initial pH of the medium and culturing time was 6.0 and 9 h, respectively. Under these conditions, S. cerevisiae 6M showed a total Se production of 10.87 mg/l, a 63% increase compared to that of with ATCC 560 under normal culture conditions.   Key words: Saccharomyces cerevisiae, organic selenium, UV mutagenesis, culture condition .