Regulation of different light conditions for efficient biomass production and protein accumulation of Spirulina platensis

Light plays an important role in the photosynthesis and metabolic process of microalgae. However, how different light conditions regulate the biomass production and protein accumulation of microalgae is mostly unknown. In this study, the influence of different light conditions, including light colors, densities, and light:dark cycles on the cell growth and biochemical composition of Spirulina platensis was symmetrically characterized. Under different colored lights, S. platensis all shows an increase trend within the increased light intensity ranges; however, each showing different optimal light intensities. At the same light intensity, different colored lights show different growth rate of S. platensis following the sequence of red>white>green>yellow>blue. The maximum growth rate and protein accumulation were determined as 21.88 and 5.10 mg/(L·d) when illuminated under red LED. The energy efficiency of different light sources was calculated and ranked as red>white>blue≈green>yellow. Transcriptomic analysis suggests that red light can promote cell growth and protein accumulation by up-regulating genes related to photosynthesis, carbon fixation, and C-N metabolism pathways. This study provides a conducive and efficient way to promote biomass production and protein accumulation of S. platensis by regulating light conditions.