The Breeding Of A High Selenium-enriched Yeast Strain And A Primary Study Of Selenium-enriched Mechanism

Selenium as an essential bio-trace element, plays a necessal living role for the health of human beings. The dietary lack of Se is related to many diseases, e.g., liver damage, heart attacks, lipids fats oxidazing impair et al. The content of se is always very low in natural food, and inorganic se can't be used in food because of its toxicity, so it is interested in the studying on the conversion inorganic se to organic se by microorganism.A selenium-resistant and selenium-enriched strain Y2 was screened from the 22 strains of yeast supplied by our lab. Y2 strain, as the original strain was mutagenesis by ⁶⁰Coγ. A highest selenium-enriched strain YR166 had been screened from many mutants of Y2. The optimum fermentation conditions of YR166 was gained by condition optimization and a L₉(3⁴) orthogonal test. The compositions of the optimization medium are 10% of wort, 1.0% of (NH4)₂SO₄,0.2% of KH₂PO₄, and the initial se concentration is 50μg/mL. Fermentation temperature is at 30℃, the volume of fermentation medium is 60 mL in 500 mL of Erlenmeyer flask; Fermentation time is for 36hs, sodium selenite was added at 6h of fermentation. Under above conditions the biomass of selenium-enriched yeast reached 14.9g/L, selenium content was 2531.4μg/g, total selenium content was 37717.86μg/g.In order to test the probability of the selenium-enriched yeast YR166 on industrial scale produce, 10L fermentator experiments were carried out. 15.4g/L of biomass and 2608.7μg/g of selenium content were gained by fermention at 30℃for 32hs in on scale of 10L fermentator. The experiment results of Erlenmeyer Flask and 10L fermentator shown that YR166 strain has the strong conversion inorganic selenium ability, and industrial potentials.Furthermore, the relation of the selenium-rich ability and the intracellular glutathione in the different types of yeast was studied. The results showed that the selenium-rich ability is in directly proportion to the intracellular glutathione concentration, the Spearman coefficient of rank correlation is 0.8939. The site of selenium binding was studied in enriched yeast, The results showed that the selenium of selenium-enriched yeast mainly bind to the sediments of broken-protoplast(membrance proteins), the selenium content is 73% of the total selenium selenium; the cell wall is only 9%; solution of cell contains 18%.