Ethephon Elicitation Enhances Biomass Accumulation and Phycobiliprotein Production in Arthrospira Platensis

Identifying factors that enhance phycobiliprotein production in photosynthetic microorganisms is important for improving pigment yields and quality, thereby supporting their cost-effective exploitation in food, pharmaceutical, and biotechnological applications. This study investigated the influence of ethephon on the growth and phycobiliprotein production of Arthrospira platensis. Arthrospira platensis was cultivated for 21 days under different ethephon concentrations to evaluate its effects on biomass, total soluble protein, and phycobiliproteins, including phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE). Samples were collected on days 7, 14, and 21, and pigment content, volumetric production, and purity index were assessed. The results demonstrated a clear concentration-dependent response. Low ethephon concentrations (0.005–0.05 mg/L) significantly enhanced biomass accumulation, protein synthesis, and phycobiliprotein production compared with the control, whereas higher concentrations (0.10 and 0.15 mg/L) exerted inhibitory effects. The highest biomass accumulation was obtained on day 21 at 0.01 mg/L, reaching approximately 2.6 g/L. Total soluble protein peaked on day 7 at 0.05 mg/L, reaching 695 ± 12 mg/g DW. The most pronounced stimulation of phycobiliproteins was observed on day 7 at 0.005 mg/L, where PC, APC, and PE reached 269.3 ± 13.8, 199.6 ± 4.1, and 77.3 ± 3.5 mg/g DW, respectively, corresponding to 1.6–1.7-fold increases over the control. The same treatment also produced the highest purity indices for PC (0.99 ± 0.05), APC (0.89 ± 0.03), and PE (0.43 ± 0.02). These findings suggest that low-dose ethephon elicitation may be a simple strategy to enhance phycobiliprotein accumulation in Arthrospira platensis.