Biorsorption Of Radioactivity Strontium By Irradiated Saccharomyces Cerevisiae

With the continuous development and utilization of nuclear energy,how to deal with the"nuclear wastes"has become a worldwide problem.The"nuclear wastes"are mainly composed of radioactive ions.Among those ions,the radioactive strontium ions are highly water-soluble,extremely contaminating.Therefore,this article aims to find a high living effective microbial adsorbent for strontium ions through laboratory evolution,to explore its adsorption behavior and mechanism,and to provide theoretical and data support for the industrialized treatment of radionuclides by microorganisms.The main research contents and results are as follow:The irradiated Saccharomyces cerevisiae was inducted by the gradient irradiation cycle induction.Moreover,through the stress pressure of strontium ions,Saccharomyces cerevisiae（Y-7）with good radiation resistance and high strontium concentration resistance was obtained.The differences between Y-7 and the original strain（K-0）were studied.The results showed that:（1）Compared with K-0,Y-7which was obtained by gradient cycle irradiation and high concentration of strontium ion stress,had greatly improved its ability to resist irradiation and high concentration of strontium;（2）Irradiation and strontium ion could change cell morphology and affect surface groups;（3）The ability of radiation resistance induced by cyclic irradiation can maintain good heredity;（4）Through the Rna-seq,we analyze the different genes between the K-4000 and K-0,those results suggested that the different genes are related to the ability of radiation resistance.From the results of adsorption experiments,Y-7 had a better adsorption ability comparing with other strains under culture coditions.The maximum removal efficiency was around 92%,and the adsoption capacity was about 22 mg g^-1.The optimal adsorption conditions were pH=7,strontium concentration is 150 mg L^-1,adsorption time=30 h,T=32℃.Moreover,the effect on biosorption ability was pH>strontium concentration>time>temperature.Langmuir isortherm can fit the adsorption behavior of Y-7 on strontium,but the adsorption process with pseudo second-order kinetics was not correct.In the competitive adsorption,we found that K⁺may promote the adsorption of strontium on Y-7due to the sharing mechanism of its ion channel and transporter,while other metal elements inhibit the adsorption.The sequence of inhibition was Ni²⁺>Fe³⁺>CS⁺>Cr²⁺>Na⁺.The recycle experiment results refleacted that the HNO₃ was the best desortion solution and the maximum desortion ability was around 85%.However,the reusability of Y-7 was not very good.Y-7 still had a better adsorption ability under extrem coditions such as:simulated high level waste water when compared to Y-0 or H-K,and the maximum adsorption capacity was 11.65 mg g^-1.The optimal adsorption condition of Y-7 was:bacterial concentration 20 g L^-1,temperature 32℃ and adsorption time 32h.Both Freundlich and Langmuir isotherm can be used to fit the adsor ption data.However,due to the complexity of the adsorption process,it is difficult to use the two models to explain the mechanism.At the same time,the thermodynamic calculation results show that the whole adsorption process is spontaneous endothermic reaction.Through TEM and EDX,it was found that the adsorption of strontium by Y-7 can be divided into cell surface adsorption and internal adsorption.In mechanism study,we used physical method to separate the cell wall,desorption experiment,functional group experiment and proteomics analysis to study the biosorption mechanism.The adsorption mechanism of strontium ions by Y-7 was discussed for surface and internal mechanism At low concentration(<50 mg L^-1),the total amount of strontium adsorbed on the surface was 75-80%;at medium concentration(100-200 mg L^-1),the total amount of strontium adsorbed on the surface was about 60%,while at high concentration(400 mg L^-1),the total amount of strontium adsorbed on the surface was 90%.Moerover,the deorption results refleacted that the ion exchange and complexation mechanism had the main contribution to adsotpion,while physical mechanism was lower.At the same time,the amino and carboxyl on the surface were the main contribution to complexation mechanism.The mechanism of intracellular adsorption was mainly studied by differential proteins.The results showed that bg12p（controlling the inflow of cell nutrients）,rsn1p（controlling the function of transmembrane transport）,and some glycolytic proteins and ion channel proteins were expressed differently.It suggested that these proteins may be involved in the transport and binding of strontium ions,and that the advantages of living biosorption agents are to transport small molecules of pollutants into cells through life activities.One-step method was used to construct a magnetic yeast adsorbent.The maximum adsorption capacity was found to be 14.74 mg g^-1.The third reusability capacity decreased by 17%compared to the first time to 12.36 mg g^-1,and the adsorption capacity kept consistent after subsequent recycling and did not decrease.Because of the strong recycling ability,the solution recovery,volume reduction ratio,and the high physical strength,etc,magnetic yeast can also become a potential material for the industrial treatment of radioactive strontium ions.