Effects of wraparound LED light quality on the growth and metabolite of C. pyrenoidosa

Microalgae are a type of single-cell autotrophic organisms with the advantages of fast growth rate and strong environmental adaptability. The carbohydrates, proteins, lipids produced by them have been widely used in food, aquaculture, healthcare and other fields. However, the high cost of cultivation has always been one of the difficulties for its industrial development. Light source is a critical environmental factor for microalgae cultivation. Existing studies have reported the effects of wavelength and photoperiod on the growth and metabolism of microalgae. Significantly, the light sources used in these studies almost are arranged on one side, and the uniformity and stability of the light distribution in the algal liquid are easily affected by the algal solution's optical diameter, algal density, and other factors. In this study, the commercial microalgae: C. pyrenoidosa was used as the research object, and the wraparound light emitting diode (LED) lights were adopted as an artificial light source for microalgae cultivation. Six light qualities of white, red, yellow, green, blue, and purple with a light intensity of 100 μmol/(m²·s) were applied to cultivate C. pyrenoidosa for 21 days. The biomass and photosynthetic pigment contents in the algal liquid were monitored daily. The protein, lipid, and carbohydrate contents in C. pyrenoidosa were determined, as well as the composition and abundance of fatty acids at the end of cultivation (D21), thereby to explore the dynamic patterns of six light qualities on the growth and metabolites of C. yrenoidosa. The results revealed that the growth rates of C. yrenoidosa cultured under green and blue LED were significantly higher than the control (white LED) from 7th and 9th day (P<0.05), respectively. At the end of cultivation (D21), the biomass in the green and blue groups increased by 24.4% and 8.0% as compared with the control, respectively. The trends of chlorophyll-a in algal liquid were similar to that of the biomass, but the total pigment of C. yrenoidosa in the green group was significantly lower than that of the purple group (P<0.05), which might be related to the low absorption and utilization rate of purple light by C. yrenoidosa (more photosynthetic pigments need to be synthesized to obtain light energy). Red LED could increase the carbohydrate content by 11.5% and reduce the lipid by 23.8% (P<0.05). Blue LED had the best positive effect on the lipid-accumulation, with a significant increment of 26.2% (P<0.05). Purple LED promoted carbon allocation from carbohydrates to protein synthesis in C. pyrenoidea. Fatty acid analysis indicated that green and purple LED significantly promoted total fatty acids (TFAs) synthesis (20.1% and 18.2%) as compared with the control group (39.5‰) (P<0.05). Moreover, green and blue LED were more conducive to the synthesis of polyunsaturated fatty acids. This study would not only provide an effective light source configuration scheme for the optimal regulation of intracellular carbon allocation of C. pyrenoidosa, but also provide some theoretical reference and technical support for the efficient and high-quality production of C. pyrenoidea.