Flocculating, emulsification and metal sorption properties of a partial characterized novel exopolysaccharide produced by Rhizobium tropici SRA1 isolated from Psophocarpus tetragonolobus (L) D.C.

Abstract

A novel exopolysaccharide (EPS) was produced by a bacterium which was isolated from Psophocarpus tetragonolobus (L) D.C. and identified as 99% Rhizobium tropici SRA1 by 16S rDNA sequencing. The flocculating performances along with emulsifying activity began simultaneously with the growth and the production of EPS and reached its utmost at 28h. EPS was purified via chilled ethanol precipitation followed by dialysis and lyophilization. The existence of hydroxyl, methoxyl, and carboxylic functional groups were confirmed by Fourier transform infrared (FT-IR) spectrum. EPS was found to be compose of 82.44% neutral sugar and 15.93% uronic acid. The average molecular weight of the exopolysaccharide was estimated as ~ 1.8 × 105. Gas-liquid chromatography indicated the presence of glucose and galactose at a molar ratio of 3:1 in EPS. In the pH range of 3-5 with EPS dosage of 15mg/l at 30°C, cation-independent flocculation greater than 90% was observed. Emulsification indices (E24) of EPS were observed as 86.66%, 83.33%, 76.66%, and 73.33% with olive oil, kerosene, toluene, and n-hexane respectively. Biosorption of Cu K [45.69wt%], Cu L [05.67wt%], Co K [15.58wt%], and Co L [11.72wt%] by EPS was confirmed by energy-dispersive X-ray spectroscopy (EDS). This report on the flocculating, emulsifying, and metal sorption properties of EPS produced by R. tropici SRA1 is unique in the literature.