Screening And Identification Of CD-Resisting Yeast Stains And Primary Studies Of The CD-Adsorption Mechanisms

Cd has been widely used in chemical industry, electronics industry, nuclear industry and other fields, every year a large number of Cd was released into environment through exhaust gas, waste water and waste residue in the world. Cd is not essential elements for biological growth and development process, considered as the highly toxic heavy metals, Cd along with Hg, As, Cr, Pb are called "SINS of element" of environmental pollution. Once getting into the body, Cd will be accumulated, causing kinds of physiological diseases, such as prostate cancer, kidney cancer and itai-itai disease, etc. Recently,"cadmium rice" and other Cd pollution incidents reports also brought a lot of negative effects to our people’s life. Therefore, the treatment of cadmium pollution is extremely urgent. Because of high cost, easy to cause the second pollution and other disadvantages, the traditional physical and chemical cadmium pollution control methods have been limited. With simple operation, high efficiency, wide range and other advantages, the microbial treatment method is more and more popular. And yeast is good material for the microbial treatment method of the environment bioremediation.2cadmium-resisting strains were screened from the16strains of yeast supplied by our lab, named as Y7and Y8, which were identified as Kluyveromyces marxianus and Rhodotorula mucilaginosa through conventional classification methods including colony characteristics, cell morphology, physiological and biochemical properties, as well as26S rDNA sequence analysis. Both Y7and Y8had high resistance and effectual adsorption to cadmium, even under cadmium concentration of50mg/L, their OD600value were above5.0, more than70%of the cadmium in the medium were removed after24hours incubation, and the optimal conditions were pH of6.0, temperature of30℃, inoculation volune5%,250mL Erlenmeyer flask with30mL fermentation medium and NaCl of3%. The distribution analysis of cadmium in different fraction of cell revealed that, for Kluyveromyces marxianus Y7, most of the adsorbed cadmium was on cell wall, but for Rhodotorula mucilaginosa Y8, most of the adsorbed cadmium was on membrane and in cytoplasm. And the cadmium adsorption reduced only a little under the treatment of DNP and DCC in Y7, but reduced a lot in Y8. These meant that, the mechanisms of adsorbing cadmium were different in the two strains, Kluyveromyces marxianus Y7mainly depended on biosorption, and Rhodotorula mucilaginosa Y8mainly depended on bioaccumulation. SDS-PAGE and RT-PCR results showed that, even50mg/L cadmium could influence protein and gene expression in Kluyveromyces marxianus Y7and Saccharomyces cerevisiae Y14, but scarcely influence protein and gene expression in Rhodotorula mucilaginosa Y8. Furthermore, zinc could reduce the biosorption ability of Kluyveromyces marxianus Y7and Saccharomyces cerevisiae Y14to cadmium, and reduce their fatality and mutation rate, also recover the protein and gene expression partly. On the other hand, zinc could increase bioaccumulation ability of Rhodotorula mucilaginosa Y8to cadmium, and increase its fatality and mutation rate.