Insights into biosynthesis, regulation, and functional potentials of exopolysaccharide from Leptolyngbya sp. MKU-05

Cyanobacterial exopolysaccharides (EPS) are natural biopolymers with substantial applications in the nutraceutical and food industries. This work included the isolation of a freshwater cyanobacterium, Leptolyngbya sp. MKU-05, and the optimization of its exopolysaccharide synthesis by response surface methodology. A central composite rotatable design yielded a maximum EPS production of 567.3mg L^- 1 under optimized medium conditions. The ExoD paralogs have a direct impact on EPS synthesis, as gene expression analysis demonstrated a 4.5-fold increase in the EPS biosynthetic gene ExoD2 relative to unoptimized conditions. Partial structural characterization of purified EPS was deduced using Fourier-Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) analysis were used to partially characterize the structure of purified EPS and validate the presence of carboxyl, hydroxyl, and amide functional groups. Monosaccharide profiling indicated arabinose as a major component. SEM and XRD analyses revealed a fibrous, porous, and semi-crystalline nature of the EPS structure. Functionally, the EPS exhibited significant anti-inflammatory and antioxidant activities compared to the commercial drug mesalazine. Toxicological assessments using human embryonic kidney cells (HEK293 cells), human erythrocytes, and Artemia nauplii confirmed the non-toxic nature of the EPS. Notably, the EPS promoted cell proliferation and improved A. nauplii survival, further supporting its biocompatibility and safety. Collectively, the EPS from Leptolyngbya sp. MKU-05 EPS is a multifunctional and safe biopolymer with promising therapeutic and nutraceutical applications.