دانلود رایگان مقاله تولید و بررسی خصوصیات اگزوپلیمر از آپاکوس رودوکوکوس

Abstract

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.

4. Conclusions

This study shows that R. opacus is a bioflocculant producing strain and this extracellular polymer is not totally solubilised in water. This is very important because this strain was earlier described as a biocollector for flotation of different minerals. Probably, this is due not only to the amphoteric behaviour of the surface of the bacterial cell wall but also to the production of extracellular polymers. This exopolymer can form flocs in the presence of kaolin and different ions. The extracellular polymer produced by R. opacus is an acidic molecule due to the mixed contributions of polysaccharide- or protein-associated COOH−, NH3 +, and phosphate groups. The exopolymer produced by R. opacus possesses all the characteristics favouring the flocculation process (the molecular weight, the presence of functional group, the acidic behaviour). This macromolecule can interact with positively charged functional groups of particles suspended in water causing their aggregation, as well as binding metal cations, e.g. Ca2+, Fe2+, Mg2+. Stabilising properties of layers of long polymer chains may also play role in the flocculation process. This characteristic indicates that the obtained polymer may be not only the good flocculating agent but also have the ability to bind heavy metal cations and modulate mineralisation of calcium carbonate.