Importance of extracellular polysaccharides on proton and Cd binding to bacterial biomass: A comparative study

Abstract

The importance of extracellular polysaccharide (EPS) on proton and Cd binding was examined by comparing the adsorption behaviors of 4 bacterial species ( Pseudomonas putida, Shewenella oneidensis, Rhizobium tropici, and Agrobacterium sp. [ATCC# 21680]) with intact capsular EPS to corresponding adsorption behaviors with the EPS enzymatically removed from the biomass. Potentiometric titrations were conducted to detect any differences in proton binding of the biomass with and without the presence of EPS. Enzymatic removal of the EPS from each of the bacterial species in this study resulted in no significant differences in biomass proton binding behavior. Batch Cd adsorption experiments also showed no significant differences in the adsorption capacities between the EPS and EPS-free systems for all 4 species of bacteria. Our results suggest that EPS contains proton-active functional groups that are similar to those on the cell wall, and that, on a mass-normalized basis, EPS and bacterial cell walls exhibit similar site concentrations and affinities for adsorbing protons and Cd from solution. Because EPS exhibits similar Cd and proton binding properties to bacterial cell walls, and because of the similarity in binding properties between species, it may be possible to model metal and proton binding to biofilms in general using a single set of stability constants. This general modeling approach would obviate the impossible task of determining binding constants for protons and each metal of interest with each EPS component and each bacterial cell wall of interest.