Studies On The Transformation Of Selenium With Yeast

Selenium(Se) is an essential micronutrient that is required in a variety of metabolic functions, and has numerous health effects. But its presence in large quantities can lead to death and deformities of wildlife. For example inorganic se can't be used in food because of its higher toxicity. Plants and bacteria have been shown to play a key role in the biological cycle of selenium by transformation from inorganic selenium to organic selenium in the environment. Generally, Selenium is trace amounts in plants. So it weighs heavily for biosynthesis of large output and cheap Se-enriched organic production by microorganism. Yeast has been selected by people for high Se-enriched ability. Started with a Yeast supplied supported by our laboratory in this paper, the breeding and condition optimization has been studied, and the expansion culture condition in fermenter is groped, which has built a favorable base for further use in industrialized production.By ultraviolet Mutagenesis we have screened and gained a strain Yeast with high biomass and resistance to Se. After fermentation experiments, we have ascertained that its biomass is up to 6.23 g/L, and its selenium content of the cells is up to 656.43μg/g, rising 1.42 times and 1.265 times as before the Mutagenesis respectively.We have found its optimum fermentation conditions by single factor and a orthogonal test under flask - shaking fermentation condition, which is as followed: juice of malt is 1%, initial selenium concentration is 20μg/ml, then add to 60μtg/ml when the fermentation of Yeast reach logarithmic phase. The inoculating content is about 10%, and then culture on the shake bed with 200 r/min at 28℃for about 29 h. Under these conditions, the biomass(dry weight) reached 8.25 g/L with the Se content of the cells being up to 1 230.21μg/g.Base on the studies of flask - shaking fermentation condition, we studied the expansion culture condition in fermenter and found its optimum fermentation conditions, which is as followed: juice of malt is 1%, initial selenium concentration is 15μg/ml, then add to 40μg/ml when the fermentation of Yeast reach logarithmic phase. The inoculating content is about 10%, and then culture in fermenter with clean air 6 L/h, 150 r/min at 28℃for about 29h. Under the optimized conditions, the biomass(dry weight) reached 8.05 g/L with the se content of the cells being up to 1003.19μg/g.The optimal condition of the yeast cell breaking was studied and finally confirmed autolyze-ultrasonic is the best through many experiments. Its optimal conditions were as below: First, yeast is dissolved in 3%NaCl adjusting pH to 5.5, and autolyze under 55℃20 h. Then followed by ultrasonic treatment, the conditions were as below: frequency is 20kHz, at 0℃for about 10min, separate time is 10s, repetition 3 times. Under the above optimal conditions, the extraction rate of protein and Se reached 65.57% and respectively.Finally we extracted protein by salting-out and found that water-soluble protein proportion of yeast total protein reached as high as 85.33%. Five components were obtained from the water-soluble protein by graded salting-out. In which the comparative content of protein obtained by salting-out with 80% ammonium sulfate reached 39.45%, and its selenium content was 897.13μg/g; the comparative content of protein obtained by salting-out with 20% ammonium sulfate reached 28.76%, and its selenium content was 1 432.46μg/g.