Alteration of the characteristics of extracellular polymeric substances (EPS) extracted from the fungus Phanerochaete chrysosporium when exposed to sub-toxic concentrations of nickel (II)

The fungus Phanerochaete chrysosporium was incubated at five sub-toxic concentrations of Ni2+ (0.5, 1, 5, 10 and 25 mg/L, respectively), and its metal immobilization ability as well as the alteration of some characteristics regarding the extracellular polymeric substances (EPS) were investigated. With the increased Ni2+ concentrations in the broth, higher Ni2+ amounts were measured in both intact fungal cells (biomass before EPS extraction) and EPS-free biomass (biomass after EPS extraction). The Ni2+ immobilization ability of the extracted EPS displayed a similar level at Ni2+ concentrations higher than 1 mg/L. The presence of Ni2+ in the broth decreased the zeta-potential of the intact biomass and increased cell surface hydrophobicity (CSH). Fourier transform infrared spectroscopy (FT-IR) analyses identified the presence of some functional groups, such as carboxyl, phosphoryl and hydroxyl groups, in the extracted EPS. The high hydrophobicity (> 60%) of the extracted EPS was decreased by the increased Ni2+ concentration. The protein (PN) and polysaccharide (PS) content in the EPS was also affected by the increased Ni2+ concentration, and the abundance of PN-like molecules ranging from 0.5 kDa to 14 kDa was enriched. However, the fluorescence characteristics and apparent molecular weight (aMW) of the extracted EPS were not affected by the Ni2+ concentration. Therefore, one possible defense mechanism developed by the fungus towards Ni2+ stress is the adjustment of its EPS composition.