Light-Driven Optimization of Exopolysaccharide and Indole-3-Acetic Acid Production in Thermotolerant Cyanobacteria

Cyanobacteria are a prolific source of bioactive metabolites with expanding applications in sustainable agriculture and biotechnology. This work explores, for the first time in thermotolerant Colombian isolates, the impact of light spectrum, photoperiod, and irradiance on the co-production of exopolysaccharides (EPS) and indole-3-acetic acid (IAA). Six strains from hot-spring environments were screened under varying blue:red (B:R) LED ratios and full-spectrum illumination. Hapalosiphon sp. UFPS_002 outperformed all others, reaching ~290 mg L−1 EPS and 28 µg mL−1 IAA in the initial screen. Response-surface methodology was then used to optimize light intensity and photoperiod. EPS peaked at 281.4 mg L−1 under a B:R ratio of 1:5 LED, 85 µmol m−2 s−1, and a 14.5 h light cycle, whereas IAA was maximized at 34.4 µg mL−1 under cool-white LEDs at a similar irradiance. The quadratic models exhibited excellent predictive power (R2 > 0.98) and a non-significant lack of fit, confirming the light regime as the dominant driver of metabolite yield. These results demonstrate that precise photonic tuning can selectively steer carbon flux toward either EPS or IAA, providing an energy-efficient strategy to upscale thermotolerant cyanobacteria for climate-resilient biofertilizers, bioplastics precursors, and other high-value bioproducts.