Phytohormone Supplementation Significantly Increases Fatty Acid Content Ofphaeodactylum Tricornutumin Two-Phase Culture

The culture of marine microalgae for biodiesel production has become a subject of interest in recent years. Environment stresses are effective at increasing lipid content at the cost of decreasing cell growth. In this study, we propose a two-phase culture where 2.5 mg L(-1)2,4-dichlorophenoxyacetic acid (2,4-D) was for the initial 5 days of culture and then 2 mg L(-1)abscisic acid (ABA) was added for another 3 days of culture, allowing both biomass and lipid increase inPhaeodactylum tricornutum. Addition of only 2.5 mg L(-1)2,4-D improved biomass accumulation by 60% and led to lipid increase nearly by 3-fold. Two-phase culture which was combined of 2.5 mg L(-1)2,4-D with 2 mg L(-1)ABA resulted in a considerable improvement both in growth and lipid production inP. tricornutum, and total lipid content was increased by 4-fold compared with no phytohormone treatment. GC-MS analysis showed two-phase culture has no significant effect on lipid components. The analysis of primary metabolites indicated that phytohormone treatment downregulated the content of carbohydrate and protein, but upregulated lipid accumulation. Gene transcriptional levels revealed that the GS/GOGAT and fatty acid synthesis pathways were induced by two-phase culture and thus accelerated fatty acid synthesis from carbohydrate and protein. This study suggests that two-phase culture combined with 2,4-D and ABA enhances the accumulation of biomass and lipid more than single phytohormone treatment inP. tricornutum.