The influence of spermidine on the build-up of fucoxanthin in Isochrysis sp. Acclimated to varying light intensities.

Spermidine is a type of important growth regulator, which involved in the biosynthesis of photosynthetic pigments, and has the function of promoting cell proliferation. In this study, Isochrysis sp. was selected as the research object to explore the effects of spermidine supplementation on the growth of algal cells and fucoxanthin synthesis under different light intensities. The results showed that the cell density (5.40 × 106 cells/mL) of algae were the highest at 11 days under the light intensity of 200 µmol·m-2·s-1 and spermidine content of 150 µM. The contents of diadinoxanthin (1.09 mg/g) and fucoxanthin (6.11 mg/g) were the highest when spermidine was added under low light intensity, and the growth of algal cells and fucoxanthin metabolism were the most significant. In the carotenoid synthesis pathway, PDS (phytoene desaturase) was up-regulated by 1.96 times and VDE (violaxanthin de-epoxidase) was down-regulated by 0.95 times, which may promote fucoxanthin accumulation.

Mixotrophic culture of bait microalgae for biomass and nutrients accumulation and their synergistic carbon metabolism.

Microalgae cannot meet the bait demand for aquaculture due to light intensity limitation and other disadvantageous conditions. This research selected 6 mixotrophic microalgae, and the optimal strains and organic carbon were screened. The results showed that Thalassiosira pseudonana and Chlorella sp. are suitable for mixotrophic culture. The maximum cell density of Thalassiosira pseudonana was found to be 1.67 times than that of the photoautotrophic group when glycerol was added. The maximum cell density of Chlorella sp. with acetic acid was 1.69 times than that of the photoautotrophic group. When the concentration of acetic acid was 5.0 g·L-1 and the concentration of KNO3 was 0.2 g·L-1, the maximum biomass of Chlorella sp. could reach 3.54 × 107 cells·mL-1; the maximum biomass of Thalassiosira pseudonana was 5.53 × 106 cells·mL-1 with 10.0 g·L-1 glycerol and 0.2 g·L-1 KNO3. Metabolomic analysis further revealed that mixotrophic bait microalgae could promote the accumulation of lipids and amino acids.