Production and Assessment of Antioxidant Activity of Exopolysaccharide from Marine Streptomyces globisporus BU2018

MICROBIAL polysaccharides are involved in a wide range of biotechnological applications. Three streptomycetes isolates isolated from marine sediment from Sharm El-Sheikh were screened for their ability to produce exopolysaccharides (EPSs) as well as the antioxidant activity. Streptomyces globisporus BU2018 producing EPS which had the highest antioxidant activity was identified based on morphological, biochemical characteristics as well as molecular analysis of 16S rRNA gene. S. globisporus BU2018 produced 8.5g/L of EPS which was fractionated to give EPSSH3 as a major fraction and subjected to determine its antioxidant activities. Maximum antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was ~ 92.9±1.3% at 1500μg/ml after 120min and the half maximal inhibitory concentration (IC50) value was 500μg/ml after 60min. Therefore, the most extreme activity against H2O2 radical was 68.5±1.48% at 1500μg/ml after 60min with IC50 value of about 1000μg/ml after 60min. Moreover, the maximum reducing power activity of exopolysaccharide SH3 (EPSSH3) was at concentration 1000μg/ml and the most extreme metal chelating activity was 90.2% at 1000μg/ml. The EPSSH3 fraction contained uronic acid (65.13%) and no sulfate. The monosaccharide composition was glucuronic acid: galacturonic acid: rhamnose: fructose through molar ratio 4.0: 3.0: 1.0: 1.0, respectively. These indicate that the fraction is acidic heteropolysaccharide. The EPSSH3 had an overall average molecular weight (Mw) of 8.15×105g/mol and number average molecular weight (Mn) of 6.36×105g/mol. Otherwise, the fourier transform infrared spectrometry analysis proposed that it belongs to a β-type heteropolysaccharide.