Production and characterisation of exopolymer from Rhodococcus opacus

• The exopolymer produced by Rhodococcus opacus shows flocculating activity.
• The water-soluble bioflocculant is glycoprotein and has acidic behavior.
• Amino sugars and uronic acids are present in its structure.
• It has fibrillar structure with high capillary forces to hold water molecules.

Screening of Actinobacteria producing exopolymers with flocculating activity was carried out. An extracellular polymer with the highest flocculating activity extracted by Rhodococcus opacus was selected to characterisation. The water-soluble fraction of this exopolymer with molecular weight of about 760 kDa was found to be 64.6% polysaccharide and 9.44% protein. Chemical analysis showed the presence of reducing sugars, uronic acids, and amino sugars at concentrations of 184.79 μg/mg, 117.6 μg/mg, and 9.23 μg/mg, respectively. Additionally, the constituent sugars of the exopolymer were glucose, mannose, and galactose. The isoelectric point was measured at 2.5, and thermogravimetric analysis indicated the degradation temperature for this fraction at 275 °C. SEM microphotography showed a fibrillar structure with a sheet-like texture of the studied exopolymer. Infrared spectrophotometry analysis revealed that the exopolymer contained carboxyl, hydroxyl, acetyl, and carboxylate groups, preferred for the flocculation process. Additionally, the presence of these groups may facilitate the heavy metals adsorption and may influence carbonate minerals formation.

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