Qualitative characterization of the protein fraction of exopolymeric substances (EPS) extracted with EDTA from sludge

Exopolymeric substances (EPS) were extracted by EDTA from activated and anaerobic granular sludge. Due to the presence of EDTA in EPS extract, interferences were pointed out for the characterization of EPS by means of the colorimetric methods and fluorescence spectroscopy. Other methods have been investigated to characterize the EPS protein fraction. Size exclusion chromatography (SEC), performed at a fluorescence excitation–emission matrix of 221/360 nm (tryptophan protein-like substances) for detection, was suitable and allowed obtaining a fingerprint of the protein-like substance fractions and determining apparent molecular weight (MW). Polyacrylamide gel electrophoresis (PAGE) was performed under either native or denaturing conditions. Various staining applications after EPS migration are effective in obtaining a protein (silver staining) or glycoprotein (PAS staining) fingerprint or MW distribution. SEC and PAGE are both appropriate techniques for the qualitative characterization of protein fractions from EPS extracted by EDTA and moreover differentiate EPS according to sludge origin and type.