Understanding the Impact of Nitrogen Availability: A Limiting Factor for Enhancing Fucoxanthin Productivity in Microalgae Cultivation

Abstract

This study aimed to investigate the regulation of fucoxanthin (FX) biosynthesis under various nitrogen conditions to optimize FX productivity in Phaeodactylum tricornutum. Apart from light, nitrogen availability significantly affects the FX production of microalgae; however, the underlying mechanism remains unclear. In batch culture, P. tricornutum was cultivated with normal (NN, 0.882 mM sodium nitrate), limited (LN, 0.22 mM), and high (HN, 8.82 mM) initial nitrogen concentrations in f/2 medium. Microalgal growth and photosynthetic pigment production were examined, and day 5 samples were subjected to fucoxanthin–chlorophyll a/c-binding protein (FCP) proteomic and transcriptomic analyses. The result demonstrated that HN promoted FX productivity by extending the exponential growth phase for higher biomass and FX accumulation stage (P1), showing a continuous increase in FX accumulation on day 6. Augmented FX biosynthesis via the upregulation of carotenogenesis could be primarily attributed to enhanced FCP formation in the thylakoid membrane. Key proteins, such as LHC3/4, LHCF8, LHCF5, and LHCF10, and key genes, such as PtPSY, PtPDS, and PtVDE, were upregulated under nitrogen repletion. Finally, the combination of low light and HN prolonged the P1 stage to day 10, resulting in maximal FX productivity to 9.82 ± 0.56 mg/L/day, demonstrating an effective strategy for enhancing FX production in microalgae cultivation.