Comparison of the complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and produced by pure bacteria strains, for cadmium, lead and nickel

This paper provides information on the metal complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and from eight pure cultures of bacteria isolated from the same activated sludge. The EPS extracted from pure bacteria cultures are mainly composed of proteins and low quantities of polysaccharides and uronic acids in comparison with EPS extracted from activated sludges. The EPS studied present two apparent pKa and the IR spectra show the presence of the same functional groups on all the EPS studied. The ability of EPS to complex Cd, Pb and Ni, was studied at pH 7 with Chau and Ruzic's models using polarography titration. All of the EPS exhibited a greater ability to complex Pb than Ni, Cd showing the weakest affinity overall. The EPS extracted from the pure cultures of bacteria were less able to complex the metals than that extracted from activated sludges. Literature data, IR data and EPS phosphorous content, supported by the EPS pKa, revealed that carboxylic and phosphoric groups may play a major role in binding to metals at pH 7. This study underlines the importance of metal exposure in order for bacteria to secrete or modify EPS. After exposure, the EPS then exhibit the greatest capacity to bind metal in order to protect bacteria from harmful effects of heavy metals.