Chemical characteristics and antioxidant activity of exopolysaccharide fractions from Microbacterium terregens

The Gram-positive bacterial strain isolated from soil was identified as the non-pathogenic Microbacterium terregens. The exopolysaccharide (CPS) produced from M. terregens was obtained by isopropanol precipitation (13.72 g L-1 growth medium), The resulted exopolysaccharide was purified by chromatography on DEAE-cellulose and Sephacryl S-200 Columns, when two polysaccharide fractions termed CPSI and CPSII were obtained. Structure features of CPSI and CPSII were investigated by a combination of chemical and chromatographic analyses, such as acid hydrolysis, methylation analysis, periodate oxidation-Smith degradation, HPLC, CC-MS, and IR. The results indicated that CPSI and CPSII were composed of glucose: mannose in a ratio of 2.7:1 and 3.21 with molecular weights 80 and 150 kDa, respectively. It has a backbone of (1 --> 4)-linked beta-glucose residues, which occasionally branches at O-6. The branches were composed of (1 --> 4)-linked beta-mannose residues. The antioxidant activity of the CPS, CPSI and CPSII was evaluated in-vitro by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay (RSA). CPSI fraction showed the highest antioxidant activity among the three fractions, with an IC50 value of 230 mu g mL(-1). The effect of molecular weight of the polysaccharide on the improvement of the antioxidant potential seems to be significant. (C) 2009 Elsevier Ltd. All rights reserved.