Study On The Characteristics Of Cadmium Adsorption Of A Rhodotorula Sp. Y11 And Purification Of Its Metallothionein

Environmental cadmium pollution is of increasing concern. Microorganisms are deemed to have great potential in treating cadmium pollution. Biosorption has emerged as one of the most promising process because of its high efficiency and favorable economics. A Yeast strain, isolated and designated as Y11 in our lab, could survive 2000mg/L of cadmium. Its characteristics and mechanism of cadmium removal were studied in this paper.According to its morphological characteristics and the ability of glucose fermentation, urease production, Fast Blue BB Salt(DBB) experimental 1 was identified as a Rhodotorula sp.Growth curve of Y11 showed the logarithmic phase began from 7 hr and stationary phase began from about 18 hr. 20hr was consided as the optimal culture time for Y11. The effect of adsorption time, the amount of biomass, and the pH on the Cd2+-adsorption by Y11 were studied. The results showed that the adsorption peak value is about 7 min and equilibrium time was about 30 min. When the initial cadmium concentrations is 48.1mg/L, with the optimum biomass quantum of 6g/L, the best removal ratio was 95.6% and Cd content of biomass reached 9‰. pH play a key effect on adsorption. Absorption of Cd2+ effectively enhanced with increasing pH. While low pH had good effect on Cd2+ desorption from biomass.Y11 had good repetitious ability of cadmium adsorption. With initial Cd2+ concentrations of 48.1mg/L in solution, after 5 absorption and desorption cycles, the cadmium absorptivity kept 90.87%~93.23%. Immobilized Yl 1 cell with gelatin-alginate can removal 77.91% Cd2+.The distribution of accumulated Cd2+ in different disposed Y11 is different too. 3.29% of the total Cd2+ can entered cytoplasm during growth culture with 100mg/L of Cd2+ in medium. But only 1% entered cytoplasm and 99% existed around cell wall when used the lyophilized biomass to adsorb cadmium.Metallothionein (MT) was found in Y11, and Cd could induce a high output of MT. When Y11 was cultured with 100mg/L cadmium, the MT content was 638.8ug/g biomass, which is 85 times of non-induced Y11 (7.51ug/g) and by far more than other Yeast strains reported to this day. After breaking up Y11 cell by glass beadings, seething solution to remove heat-sensitive proteins, MT was deposited by alcohol. The purification procedure involved gel filtration on Sephadex G-50, ion exchange chromatography on DEAE-52, and gel filtration on Sephadex G-25 and discontinuous polyacrylamide gel electrophoresis. It exhibited a clear MT stripe with molecular weight of 6500 Da in sodium dodecyl sulfate-polyacrylamide gel electrophoresis.