Adsorption process and mechanism of heavy metal ions by different components of cells, using yeast (<i>Pichia pastoris</i>) and Cu²⁺ as biosorption models

Abstract

Microbial biomass has been recognized as an essential biosorbent to remove heavy metal ions, but the biosorption process and mechanism of different components of microbial cells have not been elucidated. In present study, <i>Pichia pastoris</i> X33 and Cu²⁺ was used as a biosorption model to reveal the biosorption process and mechanism of different components of microbial cells. For the biosorption of whole cells, the maximum removal efficiency was 41.1%, and the adsorption capacity was 6.2 mg g^-1. TEM-EDX analysis proved the existence of Cu²⁺ on the cell surface and cytoplasm. The maximum Cu²⁺ removal efficiency of the cell wall, cell membrane and cytoplasm were 21.2%, 20.7% and 18.5%, respectively. The optimum pH of Cu²⁺ biosorption of the <i>P. pastoris</i> cell, cell wall, cell membrane and cytoplasm was 6. Moreover, the maximum adsorption capacity of the cell, cell wall, cell membrane and cytoplasm was 16.13, 11.53, 10.97 and 8.87 mg g^-1, respectively. The maximum removal efficiencies of <i>P. pastoris</i> biomass treated with proteinase K and <i>P. pastoris</i> biomass treated with β-mannanase were 18.1% and 28.2%, respectively. The maximum removal efficiencies of mannan and glucan were 34% and 12%, respectively. The FTIR spectra showed that the amino group (N-H), hydroxyl (O-H), carbon oxygen bond (C-O), -CH, C-N and carbonyl group (C[double bond, length as m-dash]O) of a ketone or aldehyde may interact with Cu²⁺. Thus, our work provides guidance for further understanding the effect of different cell components on biosorption.