Studies On The Potential Mechanism Of Selenium Enrichment In Saccharomyces Cerevisiae

Selenium is an essential element for life.In some areas of the world,the observed insufficiency of selenium increases the possibility of the development of a variety of disorders.Currently,selenium yeast,mainly Saccharomyces cerevisiae species,are acknowledged dietary supplements that are used to supplement deficiencies of selenium in humans all over the world.An important challenge in the selenium enriched yeast production is the toxicity of selenium which leads to a reduction in the yeast cell biomass.Herein the effect of a wide range of selenite concentrations,up to 250 mg/L,on S.cerevisiae BY4741 growth were investigated to determine the suitable selenite concentration.The data showed that at 100 mg/L,yeast cell growth was sufficient to provide an adequate cell biomass,which was about 0.4g/L.Hence,100 mg/L was the highest concentration that was used to treat yeast cells for further investigations.Secondly,in order to guide the production of selenium-enriched yeast,the potential mechanism of selenium enrichment in yeast was explored.By using ICP-AES,the effect of selenite on the contents of nine essential ions,including phosphorus,sulfur,potassium,calcium,sodium,magnesium,zinc,iron,and selenium,was detected.The data showed that selenite could significantly reduce the contents of sodium,potassium,magnesium,and phosphorus.Considering that the imbalance of essential ions in cells,especially sodium,potassium,and magnesium,may affect the permeability of the cell membrane,it may be the main cause of toxicity to cells.For another,we wondered whether selenium could be transported into yeast cells by phosphorus transporters and whether this reduced uptake of phosphorus due to the competition between them.Hence,the effect of selenite on the growth of single mutants in phosphorus transporters(pho87Δ,pho90Δ,pho84Δ,pho89Δ,pho5Δ,pho4Δ,pho86Δ)was investigated.Meanwhile,because of the similarity of selenium and sulfur,we also studied the effect of selenite on growth of sulfur transporters mutants(met15Δ,sul1Δ,and sul2Δ).The data showed a significant resistance to selenite in the pho87Δstrain,which exhibited the highest growth rate and dry cell weight.We postulated that PHO87plays a major role in selenite uptake at high concentration.In order to verify this hypothesis,an effective capillary zone electrophoresis method was established to measure selenium level.Since it is difficult to detect intracellular selenium,the total selenium concentration in yeast biomass was evaluated by measuring selenite level change in post incubated culture media.The detection of selenite could be completely achieved within 7.9 min under the condition of a mixture buffer of 85 mM Na2HP04 and 0.5 mM CTAB(pH 9.37),-5 kV separation voltage with 1.0 psi×30 s injection at 200 nm.The range of calibration curve linearity of standard was from 0 to 300 mg/L(r2=0.9999)and the recovery was 101.76%.We measured the total selenium content in wild type and pho87Δ strains by this method.The data exhibited lower selenium content in pho87Δ than that in wild type.Thus,we supposed that PHO87 overexpression would be helpful to enhance the accumulation of selenium.The strain overexpressing PHO87 was constructed,and it exhibited an increase in the cell sensitivity to selenite.In summary,the potential mechanism of selenium enrichment in yeast was investigated.The results showed that the phosphorus transporter PHO87 is involved in the accumulation of selenium in yeast.Meanwhile,we developed an effective capillary zone electrophoresis method to determine the selenium level in yeast cells.Due to the ease of sample collection and detection,this method helps to guide the production of selenium-enriched yeast.