Physicochemical and Functional Characterization of a Novel Extremophilic Exopolysaccharide Produced by Janibacter limosus

Extremophilic exopolysaccharides (EPSs) from extreme-environment microorganisms exhibit multifunctional and specific properties relevant to food, pharmaceutical, and environmental applications. This study reports the physicochemical characteristics of a novel EPS secreted by the marine actinobacterium Janibacter limosus (JlEPS) isolated from the Tyrrhenian Sea. The biopolymer was characterized for its molecular mass, monosaccharide composition, functional groups, rheological, and thermal behavior. JlEPS was found as an acidic heteropolysaccharide composed of eight sugar monomers. Neutral and acidic sugars predominate, with glucose (36.60 ± 0.46 mol%), rhamnose (23.62 ± 0.15 mol%), and galacturonic acid (16.54 ± 0.18 mol%). Amino sugars were also detected, including galactosamine (8.70 ± 0.01 mol%) and glucosamine (4.00 ± 0.10 mol%). Arabinose (7.8 ± 0.76 mol%), galactose (1.35 ± 0.01 mol%), and fucose (1.42 ± 0.06 mol%) were present in minor amounts. The average molecular weight (Mw) of the biopolymer was 1.60 × 106 Da, with a polydispersity index of 1.022, indicating a relatively homogeneous population. FT-IR indicated uronic acids and glycosidic linkages, while TGA demonstrated stability up to 250 °C. JlEPS solutions behaved as pseudoplastic fluids, and the flow curves were fitted with the Carreau model (R2 = 0.96–0.99). The zero-shear viscosity increased from 0.542 ± 0.187 Pa·s (0.5%) to (5.01 ± 0.91) × 104 Pa·s, while the flow index decreased from 0.368 ± 0.032 to 0.100 ± 0.028, confirming strong pseudoplasticity and extensive molecular entanglements. JlEPS is a complex with a defined composition and high viscosity, supporting its potential for multiple applications.