Growth and biochemical composition of Limnospira fusiformis cultivated under simulated outdoor light intensity in photobioreactors

Outdoor cultivation using natural sunlight efficiently produces valuable microalgal products, such as proteins, lipids, carbohydrates, and antioxidants but photoinhibition from intense sunlight must be minimized. This study explores the effect of varying simulated outdoor light intensity on Limnospira fusiformis growth and biochemical composition. Four light scenarios were tested to simulate varying outdoor light conditions: full sunlight (2000 µmol m⁻²s⁻¹), greenhouse (1700 µmol m⁻²s⁻¹), mid-day shade in a greenhouse (1400 µmol m⁻²s⁻¹), and whole-time shade in a greenhouse (1400 µmol m⁻²s⁻¹). Whole-time shade yielded the highest last-day dry weight (2.10 g L⁻¹), protein content (63.10 % ash-free dry weight), phycocyanin productivity (0.11 g L⁻¹d⁻¹), and lowest ash accumulation (11.00 %). High light intensity led to substantial carbohydrate accumulation, while protein synthesis and cell growth declined. This study is the first to report the correlation between high light-induced morphological changes with both protein and phycocyanin levels. Shading techniques enhanced biomass production and composition in Limnospira fusiformis. The observed improvements in protein content and phycocyanin productivity under specific light conditions demonstrate the potential for optimizing outdoor cultivation of indigenous microalgal strains, contributing to more efficient and sustainable production methods for industrial applications.