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

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, Pichia pastoris 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 P. pastoris 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 P. pastoris biomass treated with proteinase K and P. pastoris 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.