Effect of Photoperiod Duration and LED Light Quality on the Metabolite Profiles of High-Mountain Microalgal Isolates

Abstract

High-mountain microalgae exhibit remarkable adaptability to extreme environments, making them promising candidates for sustainable biorefineries. We evaluated how photoperiod (12:12, 18:6, 24:0 h) and LED spectra (cool white, full spectrum, red–blue 4:1) affect growth and metabolite formation in Chlorella sp. UFPS019 and Scenedesmus sp. UFPS021. Biomass peaked in Chlorella under red–blue 18:6 (≈1.8 g L−1) and in Scenedesmus under red–blue 24:0 (≈1.7 g L−1), revealing species-specific responses. Carbohydrate fractions were maximized under red–blue 12:12 in both species, and continuous light (24:0) depressed carbohydrate content—most notably under full spectrum. Protein content was highest under red–blue 18:6 in Chlorella sp. and under red–blue 12:12–18:6 in Scenedesmus sp. Lipid fractions increased with light duration, peaking under red–blue 18:6–24:0 in Chlorella and under red–blue 18:6–24:0—with Cool White 24:0 also high—in Scenedesmus sp. Although extended illumination favored lipids, intermediate photoperiods (12:12–18:6) provided better productivity-to-energy trade-offs and broader metabolic profiles. These results show that tuning spectral composition and photoperiod to species-specific physiology enables the targeted, energy-aware production of proteins, carbohydrates, or lipids; red–blue at intermediate durations is a robust, energy-efficient regime, whereas longer exposures can be used strategically when lipid enrichment is prioritized.