Production, characterization and bio-emulsifying activity of a novel thermostable exopolysaccharide produced by a marine strain of Rhodobacter johrii CDR-SL 7Cii.

An exopolysaccharide (EPS) producing bacterial strain was isolated from the surface of marine macroalgae (Padina sp.). Based on polyphasic taxonomy, the strain CDR-SL 7Cii was assigned to the genus Rhodobacter and found to be the closest relative of the species Rhodobacter johrii. The strain was able to produce 6.2 g/l of EPS upon fermentation using R2A medium enriched with 2.5% glucose. FT-IR analysis revealed the presence of hydroxyl, carboxyl and diacyl-ester functional groups in the purified EPS. Further Chromatographic study revealed that R. johrii synthesized a high molecular weight anionic exopolysaccharide composed of glucose, glucuronic acid, rhamnose and galactose in a molar ratio of 3:1.5:0.25:0.25. The 1D and 2D NMR spectroscopy (COSY/HSQC) analysis revealed the presence of 1,6 linked-α-d-Glcp, 1,4 linked-β-d-Glcp, 1,3 linked-β-d-GlcA, 1,3 linked-β-d-Galp, 1,6 linked-β-d-Galf and 3-α-l-Rhmp residues. Moreover, the purified EPS has shown stability towards elevated temperature and also acted as a bio-emulsifier to create a high pH and temperature stable emulsion of hydrocarbon/water indicating its industrial potential. This is the first report of EPS production by a strain of Rhodobacter johrii.