Extracellular polymeric substances of acidophilic microorganisms play a crucial role in heavy metal ions adsorption

Abstract

The influences of extracellular polymeric substances (EPS) on heavy metal ions biosorption by acidophilic microorganisms have not been systematically reported previously. In this study, three acidophilic strains were chosen as model microbes to evaluate the effect of EPS on the adsorption of heavy metal ions (Cu2+, Ni2+, Cd2+, Zn2+) from aqueous solutions. The results indicated that buffering capacities and protonation/deprotonation abilities of these acidophiles were enhanced in the presence of EPS. Acid–base titration and FTIR analysis revealed the carboxyl, phosphoryl, amino and hydroxyl groups have provided EPS binding sites for heavy metal ions via deprotonation. The extreme thermophilic archaea had the highest total site concentration of 7.93 ± 0.52 × 10−4 mol/g on the cell surface. Meanwhile, cells with EPS had better performance in adsorption when compared with cells without EPS. The biosorption abilities of the extreme thermophilic archaea with EPS toward Cu2+, Ni2+, Cd2+ and Zn2+ were 48 μmol/g, 37.5 μmol/g, 32.5 μmol/g and 28 μmol/g, respectively. This study could provide theoretical support for the treatment of heavy metal ions in acid mine drainage by acidophiles.