Promoting the Growth of Haematococcus lacustris under High Light Intensity through the Combination of Light/Dark Cycle and Light Color

The unicellular microalgae Haematococcus lacustris is an astaxanthin-rich organism that is widely used for commercial cultivation, but its main limitation is its relatively low biomass yield. It is widely accepted that the use of appropriate high light intensity could promote algal growth; however, H. lacustris is very sensitive to high-intensity light, and its growth can be readily arrested by inappropriate illumination. To exploit the growth-promoting benefit of higher light intensities while avoiding growth arrestment, we examined the growth of H. lacustris under high light intensities using various light profiles, including different light colors and light/dark cycles. The results show that light color treatments could not alleviate cellular stress under high light intensities; however, it was interesting to find that red light was favored the most by cells out of all the colors. In terms of the light/dark cycle, the 2/2 h light/dark cycle treatment was shown to lead to the highest specific growth rate, which was 46% higher than that achieved in the control treatment (18 μmol/m2·s light intensity, white light). Therefore, in further experiments, the 2/2 h light/dark cycle with red-light treatment was examined. The results show that this combination enabled a significantly higher specific growth rate, which was 66.5% higher than that achieved in the control treatment (18 μmol/m2·s light intensity, white light). These findings offer new strategies for the optimization of illumination for the growth of H. lacustris and lay the foundations for more reasonable lighting utilization for the cultivation of commercially valuable algal species.