Lead (II) adsorption efficiency and mechanisms by a heavy metal-tolerant yeast Cystobasidium oligophagum QN-3

Abstract The lead resistance and adsorption capacity of Cystobasidium oligophagum QN-3 were studied. The strain exhibited high Pb²⁺ resistance, withstanding concentrations up to 6,000 mg/L on PDA plates and 26,000 mg/L in liquid PDA medium. The Pb²⁺ adsorption capacity of QN-3 was significantly affected by Pb²⁺ concentration, temperature, pH, and incubation time. Scanning electron microscopy (SEM) revealed notable morphological changes after adsorption of Pb²⁺, including cell surface wrinkling and elongation. Fourier transform infrared spectroscopy (FTIR) identified key functional groups (–NH₂, -OH, C=O, COO-, P=O, C-N and -CH) on cell surface participating in Pb²⁺ adsorption. Chemical modification of functional groups combined with zeta potential measurements at varying pH and Pb²⁺ concentrations confirmed that electrostatic interactions and complexation were the predominant Pb²⁺ adsorption mechanisms. Pb²⁺ was primarily bound to the cell wall, with minimal intracellular accumulation. The decreased Pb²⁺ uptake observed in the presence of metabolic inhibitor DCC suggested an ATP-dependent transport process following initial surface biosorption. Pretreatments including ultrasonication, boiling and alkaline treatment enhanced Pb²⁺ adsorption efficiency. The exceptional Pb²⁺tolerance and adsorption capacity of Cystobasidium oligophagum QN-3 highlighted its potential for bioremediation applications.