Copper-binding characteristics of exopolymers from a freshwater-sediment bacterium

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Abstract
Cu-binding activity by exopolymers from adherent cells of a freshwater-sediment bacterium was demonstrated by a combination of equilibrium dialysis and flameless atomic absorption spectrometry. Crude, cell-free exopolymer preparations containing protein and polysaccharide components bound up to 37 nmol Cu/mg (dry wt). A highly purified exopolysaccharide preparation bound up to 253 nmol of Cu/mg of carbohydrate. The conditional stability constant for the crude exopolymer-Cu complex was 7.3 .times. 108. This value was similar to those obtained for Cu complexes formed with humic acids and xanthan, an exopolysaccharide produced by Xanthomonas campestris. Studies conducted at Cu concentrations, pHs and temperatures found in sediments from which the bacterium was isolated indicated that the exopolymers were capable of binding Cu under natural conditions.