Biofilm formation in Streptomyces nigra strain KDS4 and characterization of extracellular polymeric substances (EPS) for biomaterial development.

Biofilm formation in marine Streptomyces is a dynamic yet poorly understood process, that limits their functional exploitation. This study investigated the biofilm development and extracellular polymeric substances (EPS) synthesis by Streptomyces nigra strain KDS4, a promising marine Actinobacterium, aiming to optimize EPS yield and characterize its bio-functional properties. Biofilm and EPS formation began with spore germination and hyphal growth, maturing by 60 h with dense hyphal intertwining, sporulation, and EPS secretion, followed by dispersal at 84 h. The bacterium showed the highest biofilm height (~ 2.35 μm) over the polypropylene substrate. Upregulated expression of the cslA gene, associated with biofilm matrix production, was confirmed during biofilm development. Structural analysis of EPS revealed α- and β-glycosidic linkages, hydroxyl, and alkyne groups, along with an amorphous morphology and diverse elemental composition. EPS exhibited thermal transition up to 300 °C and antioxidant and emulsifying properties. Notably, EPS demonstrated hydrogel-forming capability, with 5% (wt/wt) EPS-based hydrogel exhibiting rapid gelation (73 s), high porosity and pore size (31.66 μm), excellent swelling (53.54%), and strong viscoelasticity (G' > G''). At 20% (wt/wt) EPS, the hydrogel achieved a compressive strength of 36.83 kPa, demonstrating its mechanical robustness. These findings highlight S. nigra strain KDS4 as a promising source of multifunctional EPS for sustainable environmental and biomedical applications. While the study provides detailed in vitro insights, evaluation of EPS functionality and biocompatibility remain to be explored. Future work should focus on scale-up production, structural-functional correlations, and validation of EPS-based hydrogels in environmental remediation and biomedical models.