Characterization of a bioactive exopolysaccharide extracted from a hot spring-originated cyanobacterium, Scytonema...

The extracellular polymeric substance (EPS) produced by a hot spring-dwelling cyanobacterium (Scytonema ambikapurensis) was extensively characterized to elucidate its composition, structure, and functional potential. Alcian blue staining confirmed substantial EPS production with uronic acids and sulfated groups. Biochemical assays indicated a carbohydrate-rich matrix (717 μg mg^-1 dried EPS) with negligible protein (0.2 μg mg^-1), supported by CHNS analysis (29.71% C; 3.34% H; 1.54% N; 1.02% S). The EPS exhibited high solubility (74%) and water-holding capacity (8.86 g g^-1EPS), suggesting suitability for hydrogel formation, soil conditioning and moisture-retention applications. AFM and SEM revealed a fibrous, porous network, while XRD demonstrated semi-crystallinity (54.60%), indicating balanced flexibility and rigidity of EPS. The negative zeta potential (-30.65 mV) reflected abundant anionic groups and colloidal stability. FTIR detected hydroxyl, carboxyl and sulfate groups, whereas, NMR and HPLC analysis revealed a β-(1 → 4)-linked gluco-mannan backbone with C3-linked branches composed of arabinose (38.29%), mannose (15.69%), glucose (14.34%) and glucuronic acid (8.55%), indicating a novel cyanobacterial EPS. Functionally, the EPS exhibited strong emulsifying capacity (67.91%), high antioxidant activity (up to 74.42%) and concentration-dependent antibacterial activity, with maximum inhibition (21.50 mm) against Kocuria rosea. These findings establish S. ambikapurensis EPS as a structurally distinct, multifunctional biomaterial with applications in environmental remediation and industrial formulations.