Identification of <i>Desmonostoc</i> sp. BTA-330: assessment of growth kinetics and biochemical characterization of exopolysaccharide

The cyanobacterial strain BTA-330 was evaluated for its potential to produce exopolysaccharides (EPS) under nitrogen-deprived photoautotrophic conditions. The strain was initially identified through a polyphasic approach as <i>Desmonostoc</i> sp., BTA-330. The strain depicted biomass concentration of 1.23 g/L and total EPS of 367.87 ± 5.4 mg L^-1 in 30 days with capsular-EPS (CPS) and released-EPS (RPS) of 218.67 ± 2.5 and 149.2 ± 2.9 mg L^-1, respectively. Biomass composition analysis (in % w/w, DCW) showed total protein of 34% with 26.02% of total proteins comprising phycobiliproteins, followed by carbohydrates (32%), lipids (16%), nucleic acid (8%), other pigments (1.7%), and ash (7%). Kinetic studies revealed both CPS and RPS as secondary metabolites with maximum accumulation during the stationary phase of growth. The analysis of EPS composition showed abundant carbohydrate content of 80% (w/w, dry cell weight), followed by protein and nucleic acids. The subsequent characterization of both EPS using SEM, FTIR, and rheometer revealed the morphology, distinct functional groups, and their pseudoplastic behaviors, respectively. Further analysis demonstrated significantly high flocculating rate (39.4 ± 1.3 to 51.78 ± 1.3), DPPH scavenging (37.74 ± 1.5 to 39.76 ± 1.3), and hydroxyl ion scavenging (57.46 ± 1.2 to 69.53 ± 1.2) activities. Thus, <i>Desmonostoc</i> sp. BTA-330 is a unique source of EPS with potential applications in the food and pharma industries.