Effect of exopolysaccharides on the adsorption of metal ions by Pseudomonas sp. CU-1

Pseudomonas sp. CU-1, which was isolated from an interfacial biofilm of a sludge sample collected from an electroplating company, had a relatively high ability to adsorb Cu^2 + in solution. The bacterium grown in broth culture produced a large amount of capsular exopolymers mainly consisting of polysaccharides. The exopolysaccharides (EPS) were partially purified. The adsorption isotherm experiments showed that cells and EPS of Pseudomonas sp. CU-1 had similar Q⁰ and b for the dye, Janus Green, and Cu²⁺. The adsorption of Cu^2 + by cells could be monitored by the amount of dye displaced, due to the binding of metal ions onto the cell surface. The order of adsorption ability of metal ions and dye displacement by metal ion of the bacterium was: Cu^2 +> Cd^2 +> Zn^2 +> Ni^2 +. The results of the dye displacement by metal ions binding onto the surfaces of cells, EPS-removed cells, and EPS suggest that EPS produced by Pseudomonas sp. CU-1 plays an important role in preventing metal ions in the surrounding environment from contact with the bacterial cells. The possible role of the metal ion adsorption by the EPS of this biofilm bacterium was discussed.