Mimicking sunlight like photoperiod with colored LEDs to boost productivity of greenhouse protein farming during unfavorable weather conditions : a microalgae based study

The reliability of microalgal technologies on regular availability of light for photosynthesis and continuous biomass production has an adverse impact on their long-term and large-scale applicability. Microalgae, identified for their high productivity per unit area compared to other photosynthetic species typically use sunlight as basis light to perform photosynthesis and accumulate intracellular metabolites. Photosynthetic efficiency i.e. percentage of available light stored as chemical energy in biomass influences the type and quantity of metabolite accumulated. However, continuous usage of sunlight can be limited as it is highly variable across seasons, unstable due to clouds blocking certain wavelengths and scarcely available during winter. In this study, we investigated the effect of simulated sunlight-like environment with LEDs of different wavelengths on productivity of Chlorella sp. in a 3-litre photobioreactor. A sinusoidal profile with maximum intensity of 100 µmol/m2/s (representative of winter) of red, blue and white colors with a photoperiod of 16:8 hours light/dark was applied for 15 days. Cell growth and pigment accumulation was assessed under non-axenic conditions in WC medium. Imaging flow cytometry and biomass analysis showed that cells grown under red light had higher final concentration (258 million cells/mL), dry weight (1.78 g/L) and pigments (14.9 mg/g) than blue light with 42 million cells/mL, 1.38 g/L and 6.3 mg/g respectively. Furthermore, 13% more cells were produced in red light compared to white light. Extended research in this direction could envisage artificial lighting as a promising strategy to supplement sunlight, boost productivity and steer specific light color-based algal metabolite accumulation.