Carotenoid accumulation in aerial microalga Coelastrella rubescens KGU-H009 in light- and nitrogen-stress conditions

Some natural carotenoids remain unexplored in terms of their function because they occur only in trace amounts, or their stereochemistry is unclear. It is expected that scientists will discover new physiological activities that have a positive impact on human heath by analysis of such carotenoids. The purpose of this study was to analyze the carotenoids synthesized by the novel aerial microalga Coelastrella rubescens KGU–H009, and the dynamics of their accumulation. Cultivation experiments were conducted for 7 days at 25 °C, combining different light conditions with the presence or absence of nitrate ions. Short-term (2-h) cultivation was also performed, and tests were conducted with the addition of the inhibitor of photosynthesis 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU). Strain KGU-H009 exhibited its highest carotenoid content (34.5 mg g⁻¹) in the presence of nitrogen sources and strong light. Upon nitrogen source depletion, the content of zeaxanthin and β-carotene decreased, while the content of astaxanthin and adonixanthin increased. Strain KGU-H009 exhibited reversible control of the xanthophyll cycle to adapt to changes in light intensity, but the xanthophyll cycle was inhibited by the addition of DCMU. Strain KGU-H009 demonstrated the ability to synthesize carotenoids involved in both light harvesting and photoprotection, suggesting its adaptability to environmental change.