Photoautotrophic Production of 2-O-α-D-Glucosylglycerol by Marine Cyanobacterium aponinum SCSIO-45682: Multi-Factor Optimization and Functional Evaluation

Glucosylglycerol (GG) is a compatible solute with excellent moisturizing capacity and macromolecule stability, exhibiting broad application potential in cosmetics, food, and pharmaceutical industries. The halophilic cyanobacterium Cyanobacterium aponinum SCSIO-45682 can synthesize GG under salt stress and represents a promising strain for photoautotrophic GG production. In this study, the GG product extracted from SCSIO-45682 was structurally identified as 2-O-α-D-GG by high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) analysis. The effects of salinity, initial pH, light intensity, and carbon, nitrogen, and phosphorus concentrations on biomass and GG accumulation were systematically investigated using single-factor experiments, and response surface methodology (RSM) was subsequently applied to optimize intracellular GG content as a percentage of dry weight (% DW). The results showed that salinity was the primary factor driving GG accumulation in SCSIO-45682. As salinity increased from 30 ppt to 120 ppt, GG content increased by 3.41-fold. Light intensity was another key factor affecting GG accumulation, with moderate irradiance of 2000–5000 lux being more favorable for GG accumulation. Among the nutritional factors, nitrogen and phosphorus had relatively weak effects, whereas increasing carbon concentration enhanced GG yield by promoting biomass accumulation. The RSM results showed that salinity × light intensity exhibited a synergistic enhancement pattern, whereas the pH × carbon concentration interaction displayed an inverse regulatory effect. Under the optimal conditions of 96 ppt salinity, pH 5.0, 5000 lux light intensity, and 7.0 mM NaHCO₃, GG content and yield reached 16.30% DW and 366.75 mg/L, respectively, representing a 3.29-fold increase compared with the control. In addition, the GG-containing crude extract exhibited concentration-dependent 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid, ABTS) radical-scavenging activities. Overall, this study achieved a high level of natural 2-O-α-D-GG accumulation in a wild-type cyanobacterial photoautotrophic cultivation system through multi-factor synergistic optimization, providing a foundation for the green biomanufacturing of GG using wild-type C. aponinum.