Cadmium binding characterization and mechanism of a newly isolated strain Cystobasidium oligophagum QN-3

The aim of this study was to screen a strain for the removal of Cd²⁺ from aqueous solution and investigate the characterization and mechanism of the Cd²⁺ binding process. A novel strain of yeast showed high tolerance of cadmium, namely Cystobasidium oligophagum QN-3, was isolated from soils, which could resist 22,000 mg/L and 18,000 mg/L Cd²⁺ on PDA (potato dextrose agar) plate and in PDA liquid medium, respectively. Cd²⁺ binding experiment showed that the strain could remove Cd²⁺ from aqueous solution effectively, the maximum Cd²⁺ removal rate of 84.45% was achieved at initial Cd²⁺ concentration 30 mg/L. Scanning electron microscopy (SEM) analysis revealed that sorption of Cd²⁺ by cells could be associated with changes in the cell surface morphology. Fourier transform-infrared spectroscopy (FTIR) analysis confirmed the important role of the functional groups  OH, CO,  NH₂, COO , PO, and CH on the cell surface in the binding of Cd²⁺. The comparison of the binding ability of different cellular parts indicated a significant role of the cell wall played in the Cd²⁺ binding process. Pretreatment of the cells by boiling or ultrasonication could improve the biosorption capacity of QN-3. In addition, QN-3 exhibited selective and preferential property of binding capacity for other heavy metals, such as Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ni²⁺. These data suggested the promising use of Cystobasidium oligophagum QN-3 as an effective and friendly biosorbent for cadmium or other heavy metals decontamination in the environment.