Characterisation of extracellular polysaccharides from bacteria isolated from a full-scale desalination plant

Bacterial extracellular polymeric substances (EPS), particularly slime consisting of high-molecular weight soluble exopolysaccharides contribute significantly to seawater reverse osmosis (SWRO) membrane fouling. In this study, we characterized the soluble exopolysaccharides of 25 model bacterial strains isolated from different locations of a full-scale desalination plant in Western Australia. Biofilms of individual strains were initially quantified using crystal violet assay; significant biofilm production was detected in 21/25 isolates. Enzyme-linked lectin sorbent assay using lectins, Conacavalin A (ConA) and Ulex identified glucose and/or mannose in 11/25 isolates, and fucose in 24/25 isolates to significant levels. Exopolysaccharides were extracted and purified from bacterial cultures using centrifugation, TCA precipitation, cold acetone precipitation, dialysis and vacuum drying. Yield of exopolysaccharides varied between 90 mg to 480 mg/L of broth culture. Purified exopolysaccharides of 14 strains were analysed by High-Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD) and ATR-FTIR. Fucose, rhamnose, glucuronic and galacturonic acids were present in majority of the isolates. These sugars are common to polysaccharides of glycosphingolipid-producing bacteria, a predominant subset of RO membrane biofilm community of the full-scale plant. They are known to impart better physical integrity to EPS and form strong, sticky recalcitrant biofilms. Mannose, glucose, galactose, xylose and ribose were also present.