Manipulating light quality as a technique to optimize the production of biomass, phycocyanin and protein in Limnospira platensis

The aim of this study was to investigate the synergistic effect of wavelength and irradiance on growth, photosynthetic activity, and biochemical composition of the cyanobacterium Limnospira platensis. In the first experiment, the effect of twelve different wavelengths (ranging from 415 to 730 nm) and five different irradiances at each narrow wavelength range on the metabolic response of the microalgae regarding growth and photosynthetic activity in terms of electron transport rates (ETRs) of L. platensis were investigated. Results from experiment 1 indicated that specific growth rates at and biomass according with the total photons received were maximum at wavelengths close to yellow (585–590 nm) (0.011 ± 0.0001 day−1(mol m−2)−1 and orange (600 nm) regions (~ 6 g L−1(mol m−2)−1, respectively. ETRs close to green (500, 520, and 570 nm) and red (665 and 685 nm) wavelength regions indicated elevated photosynthetic activity by L. platensis. In experiment 2, the assessment of four different light colors (white, green, yellow and red) as a stimulus for phycocyanin and protein accumulation in L. platensis biomass were studied. Results suggested that exposing L. platensis to white and red light-types tend to increase the specific growth rate (µ = 0.12 day−1), biomass concentration (~ 38.00 × 104 filament mL−1) and phycocyanin content (~ 2.6 mg g−1). Peak of in vivo chlorophyll a, expressed as relative fluorescence unit (RFU), in L. platensis after 4 days of cultivation occurred in the presence of red light. The green and yellow light-types influenced the synthesis of intracellular protein (~ 500 mg g−1). This study analyses how varying light spectra affect L. platensis physiology, offering essential data to optimize biomass growth and the synthesis of high-value compounds, such as protein and phycocyanin.