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

Abstract

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 (20–100 kDa). Denatured proteins with a polysaccharide moieties characterization are more present in B-EPS. Glycoproteins with α-d-mannosyl and/or α-d-glucosyl (90, 50, 40 kDa) were detected. Proteoglycan-like and sulphated proteoglycan-like substances are also detected, mainly in B-EPS. A 68 kDa sulphated proteoglycan-like substance contains two glucidic residue types: α-d-mannosyl and/or α-d-glucosyl and N-acetyl-β-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.).

Keywords:

• extracellular polymeric substances
• anaerobic granular sludge
• glycoproteins
• sulphated proteoglycans
• SDS-PAGE

Acknowledgements

Dr P. Lens (UNESCO-IHE of Delft, The Netherlands), Dr E. Van Hullebusch (Université Paris-Est, France) and Smurfit Company (Saillat-sur-Vienne, France) are acknowledged for providing anaerobic granular sludge.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at doi:10.1080/09593330.2015.1034186.

Funding

The authors thank the Regional Council of Limousin (France) for their financial support.