The effect of LED light irradiation and phosphate concentrations on the biological activity of Fischerella Sp

Environmental factors significantly influence the growth, metabolism, and biosynthesis of bioactive compounds in cyanobacteria, with light playing a crucial role. In this study, we investigated the combined effects of LED light wavelengths and phosphate concentrations for the first time on the growth and biological activity of Fischerella sp. to optimize the production of bioactive metabolites. Unlike previous studies that mostly addressed either light or nutrients independently, our work integrates both factors to provide a novel perspective on light–nutrient interaction in cyanobacteria. Fischerella sp. was cultivated for 30 days in Z8 medium under white, blue (470 nm), green (520 nm), and red (660 nm) LED lights, with varying phosphate concentrations (0.02–0.08 g/L K2HPO4). The corresponding light intensities were approximately 45, 36, 33, and 10 μmol photons m−2 s−1 for white, blue, green, and red LEDs, respectively. Biological indices, including dry weight, specific growth rate (SGR), cell doubling time (Tg), and total phenolic, flavonoid, tannin, and protein content, were measured. Additionally, antioxidant activity was evaluated using DPPH and ABTS assays, and enzymatic activities of catalase, superoxide dismutase, and glutathione S-transferase were determined. The cytotoxicity of the extracts on human gastric cancer cells (AGS) was assessed using the MTT assay. All measurements were performed in triplicate. Statistical analysis was performed using ANOVA followed by Tukey's test, with significance set at p < 0.05. The highest dry weight was observed under red light treatment, followed by blue light, whereas the lowest value was recorded under green light. Red and blue light significantly increased dry weight compared to green light, with red light showing the most pronounced effect. The specific growth rate (SGR) was highest in the early days but significantly decreased over the 30-day period. The longest cell doubling time (Tg) was observed under red light, while the shortest was recorded under green light. Red light treatment led to the greatest accumulation of total phenolics, flavonoids, tannins, and proteins compared to other treatments. Antioxidant activity was also highest under red light treatment. Antioxidant enzyme activities significantly enhanced under red light, indicating improved oxidative stress defense. Red light also induced elevated levels of malondialdehyde (MDA), suggesting enhanced oxidative stress and simultaneous activation of antioxidant defenses. The MTT assay confirmed a dose-dependent cytotoxic effect of the extracts against gastric cancer cells. Cell viability was highest under green and white light treatments and lowest under red light. Red light significantly enhanced the production of bioactive compounds and increased the antioxidant and anticancer activities of Fischerella sp., with higher phosphate concentrations (up to 0.08 g/L) boosting these effects. These findings demonstrate that red light, combined with phosphate optimization, offers a promising approach to enhance the biotechnological value of cyanobacteria for pharmaceutical applications.