Selective antibacterial activity of crystalline extracellular polysaccharide extracted from isolated microalgae...

Microalgae-derived extracellular polysaccharides (EPSs) have emerged as a promising biological macromolecule for its application in pharmaceutical and biotechnological fields due to its diverse physicochemical and biological activities. In this study, an isolated microalgae (Asterarcys quadricellulare) was cultured in photobioreactor under the light condition by maintaining 14:10 photoperiod to produce EPSs. The yield of EPSs was found 0.392 ± 0.027 gL^-1. The biochemical analysis of extracted EPSs had shown the presence of uronic acid (0.42 ± 0.05%), phosphate (0.312 ± 0.013%), sulfate (0.531 ± 0.04%), and carbohydrates (60.33 ± 0.02%) containing glucose and galactose with a ratio of 3.24:1. FTIR analysis of EPSs revealed characteristic glycosidic bond between sugar monomer at 880 and 834 cm^-1. Therefore, extracted EPS was a complex heteropolysaccharide structure. Surface morphology of EPSs revealed the presence of a large number of symmetrical and regular filamentous repeating units. XRD analysis had shown the crystalline nature of extracted EPSs with crystallinity index of 51.73%. Antimicrobial activity of EPSs was evaluated against Bacillus subtilis (gram positive) and Escherichia coli (gram negative) bacteria. Escherichia coli had showed 46.67 ± 0.002% growth inhibition and 33.3 ± 2.5% (P < 0.01) reduction in the viable cell count compared to the negative control. Results demonstrated the promise of microalgal EPSs in the biotechnology and pharmaceutical sectors for selective antimicrobial application.