Evidence of glycoproteins and sulphated proteoglycan-like presence in extracellular polymeric substance from anaerobic granular sludge

The protein fraction of extracellular polymeric substance (EPS) from two anaerobic granular sludge samples was characterized with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and a far western blotting method. SDS-PAGE was used with various staining applications to obtain a protein (silver), glycoprotein [periodic acid-Shiff's (PAS)] or proteoglycan-like (Alcian blue at pH 2.5 (carboxylic group) or 1 (sulphated group)) fingerprint. The fingerprints of the EPS denatured protein from the two sludge samples differed. Some proteins are specific to Soluble (S) or Bound (B)-EPS (20-100kDa). Denatured proteins with a polysaccharide moieties characterization are more present in B-EPS. Glycoproteins with alpha-D-mannosyl and/or alpha-D-glucosyl (90, 50, 40kDa) were detected. Proteoglycan-like and sulphated proteoglycan-like substances are also detected, mainly in B-EPS. A 68kDa sulphated proteoglycan-like substance contains two glucidic residue types: alpha-D-mannosyl and/or alpha-D-glucosyl and N-acetyl-beta-D-glucosamine. Such heteroproteins are present around the membrane as well as the surface-layer from Archaea and from some bacteria. The glycoprotein and sulphated proteoglycan-like substance are assumed to contribute to anaerobic granule strength, thanks to their ability to perform interactions of various nature (ionic, hydrophobic, Ca2+ as divalent cation bridging, etc.).