Abstract
Fucoxanthin (Fx), a kind of primary carotenoids in brown seaweeds and diatoms, has attractive efficacy in human’s healthcare including loss weight, the prevention of diabetes and Alzheimer’s disease. Marine diatom Phaeodactylum tricornutum is now realized as a promising producer for commercial Fx production due to its higher content of Fx than brown seaweeds with easily artificial cultivation and Fx extraction. In the present study, to improve Fx production in P. tricornutum, the mixotrophic cultures were applied to optimize initial cell density, light intensity, light regime and nitrogen supplementation. The results showed that the higher initial cell density (1 × 107 cells mL–1) and lower light intensity (20 μmol m–2 s–1) were favorable for biomass production and Fx accumulation. The maximal Fx content [16.28 mg g–1 dry weight (DW)] could be achieved under blue light (BL), but the highest biomass concentration (5.53 g L–1) could be attained under red: blue light (R: B, 6:1) in the batch culture. A novel two-phase culture approach was developed to increase the biomass concentration to the highest value (6.52 g L–1) with the maximal productivity of Fx (8.22 mg L–1 d–1) through light shift from R:B ratio (6:1) in phase 1 to R:B ratio (5:1) by enhancing BL and tryptone addition in phase 2. The content and intracellular amount of Fx were also increased 8% and 12% in phase 2 compared to phase 1. The expression levels analysis revealed that genes encoding phytoene synthase (PSY), zeaxanthin epoxidase (ZEP), and fucoxanthin-chlorophyll-protein b (FCPb) were upregulated significantly, with downregulation of the gene encoding violaxanthin de-epoxidase (VDE), leading to the improvement of Fx in phase 2. The present study demonstrated the two-phase culture strategy could promote Fx productivity through enhancing biomass production and increasing Fx content, indicating that strengthening BL coupled with adding tryptone were effective to facilitate Fx production by mixotrophic cultivation of marine diatom P. tricornutum.
Highlights
Fucoxanthin is a kind of primary carotenoids and draws increasing attention because of its functions of anti-oxidant, antiobesity, and anti-cancer as well as effects against Alzheimer’s disease (Vilchez et al, 2011; Fu et al, 2015; Xiang et al, 2017)
Marine diatom P. tricornutum CCMP 1327 was kindly provided by Dr Hanhua Hu in Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
For improving biomass and Fx production in a shorter time, the highest initial cell density was the option in the following experiments
Summary
Fucoxanthin is a kind of primary carotenoids and draws increasing attention because of its functions of anti-oxidant, antiobesity, and anti-cancer as well as effects against Alzheimer’s disease (Vilchez et al, 2011; Fu et al, 2015; Xiang et al, 2017). Most strains of P. tricornutum could use glycerol and urea as organic carbon and nitrogen source, and biomass could reach to 3∼15 g L−1 under mixotrophic mode (Garcia et al, 2005; Huang et al, 2015; Nur et al, 2019). The mixotrophic P. tricornutum has not been applied in large-scale cultivation system because of the technological barriers mainly on the big risk of contamination when use organic nutrients in open system (Matsumoto et al, 2017). The content of carotenoids in P. tricornutum under mixotrophic conditions was usually 0.5∼0.7% of DW, in which Fx portion was even lower (Ceron-Garcia et al, 2013; Patel et al, 2019). It seems difficult to achieve high biomass and high Fx content simultaneously, resulting in the low productivity of Fx by mixotrophic P. tricornutum. Developing an applicable approach of mixotrophic P. tricornutum is vital to commercial production of Fx
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