Abstract Description

The marine environment boasts the largest aquatic ecosystem on Earth and shelters microorganisms that represent more than half of the total biomass of prokaryotes in the world. Consequently, marine bacteria represent an underexplored source of extracellular polysaccharides (EPS), that may possess unique properties with biotechnological potential. In this study, 28 marine invertebrate-associated bacterial strains were screened for EPS production in Zobell marine medium supplemented with 30 g/L glucose. Strain S.105, isolated from the marine sponge Hymeniacidon perlevis (H. perlevis), produced the highest EPS yield and analysis through the Genomic Taxonomy Database (GTDB) suggests that S. 105 may represent a novel lineage within the family Rhodobacteraceae. EPS production was further assessed by subjecting S. 105 to varying cultivation conditions, including glucose concentration (0, 10, and 30 g/L) temperature (18°C and 30°C), and incubation time (up to 14 days). Compositional analysis of the purified EPS was subsequently characterized. Strain S. 105 produced a high molecular weight EPS (>50 kDa) with a maximum yield of 1.24 g/L after 14 days. Assay-based analysis of the purified material revealed that carbohydrates accounted for most of the dry weight (62%), followed by uronic acids (22%), proteins (12%), and sulfate groups (3%). Gas chromatography coupled with mass spectrometry (GC-MS) analysis of the hydrolyzed EPS showed a distinct monosaccharide profile comprising glucose (59%), galactose (16%), glucuronic acid (7%), and methyl-glucuronic acid (18%). The presence of uronic and methylated sugars, as well as sulfate substituents, suggests a structurally complex polymer with potential functional properties. To our knowledge, no EPS from a Rhodobacteraceae affiliated bacterium has been reported with this compositional profile (glucose, galactose, glucuronic acid, methyl-glucuronic acid). These findings highlight the biotechnological promise of marine bacteria as sources of novel carbohydrate polymers, with future work directed at in-depth structural and functional characterization.