Extracellular Polysaccharide From Marine Streptomyces sp. KAR3: Structural Characterization, Antibacterial, and Anticancer Potential

ABSTRACT

Marine environments are an abundant source of sustainable polymers with considerable biomedical potential. In this study, a marine Streptomyces sp. strain KAR3 was isolated from the Gulf of Mannar. Extracellular polysaccharide (EPS) was isolated, characterized, and evaluated for its antibacterial, antibiofilm, and anticancer activity against MDA‐MB‐231 cells. Strain identification using biochemical characterization and 16S rRNA gene sequencing (Accession: PP330035) showed 100% similarity to Streptomyces geysiriensis , and phylogenetic analysis supported its affiliation with the S. geysiriensis clad. S. geysiriensis strain KAR3 produced 4.4 g/L of EPS in the media after 7 days. EPS production was optimized in several culture media and structurally characterized by UV spectroscopy, Fourier transform infrared (FTIR), ¹ H and ¹³ C nuclear magnetic resonance (NMR), and GC–MS. FTIR analysis revealed C–H and C = O stretching and glycosidic linkages. ¹ H and ¹³ C NMR shifts aligned with sugar moieties, indicating the EPS is a complex polysaccharide. GC–MS showed glucose as the major monosaccharide in the EPS. The isolated EPS exhibited dose‐dependent inhibition, with the largest zone of inhibition observed at 100 µg/mL. The EPS exhibited notable antibacterial and biofilm inhibitory activity against Staphylococcus aureus , Klebsiella pneumoniae , Escherichia coli , and Enterococcus faecalis in a concentration‐dependent manner. The minimum inhibitory concentration (MIC) calculated for the most susceptible strains was at 100 µg/mL. The IC ₅₀ value of EPS was found to be 25.44 µg/mL, indicating a strong cytotoxic effect against MDA‐MB‐231 cancer cells. Together, these findings demonstrate the broad‐spectrum antibacterial and anticancer activity of marine EPS from S. geysiriensis and its potential as a natural source in the search for new antimicrobial compounds.