Project description:Phytoplankton lipids, such as microalgae lipids, are important compounds of increasing interest in bioenergy, food, pharmacy, aquaculture and ecology for their high molecular diversity. There is a taxonomically diverse lipid response under P stress with unresolved questions related to the diversified mechanism behind the lipid responses. A marine microalgae with high EPA content was isolated, named Nannochloropsis sp. PJ12. We reveal a mechanism of phosphorus-induced lipid class remodeling in Nannochloropsis sp. PJ12 based on highly corresponding transcriptome and lipidome data. Phosphorus- deprivation leads to the rapid reduction of phospholipids (PL) and synthesis of the betaine lipids (BL). Phosphorus-complement recovers the content of PL and BL to the original level. The changes are mediated mainly by a glycerophosphoryldiester phosphodiesterases on the transcriptome level. To adapt to low phospholipids, the transcription levels of gene encoding P transporter were upregulated. When Nannochloropsis sp. PJ12 was once again under phosphorus-complement, some of gene encoding P transporter continue to increase on the transcription levels. The novel phospholipid-remodeling scheme opens new avenues for metabolic engineering of lipid composition in algae.
Project description:Oleaginous microalgae Nannochloropsis spp. are considered to be promissing species for production of biofuels and biomaterials. Nevertheless, its biofuel production remains to be economically unviable. Hence, further improvement of cultivation conditions and genetic traits for high-lipid contents without affecting growth is required. To understand genes involved in neutral lipid accumulation upon nitrogen deprivation (ND) in a novel isolate of Nannochloropsis sp. PJ12, we performed comparative transcriptomic and lipidomic analyses of cells under ND and NR (nitrogen replete) conditions. Transcriptomic profiling indicated that, while enzymes involved in TCA cycle in PJ12 under ND condition were upregulated compared to that under NR condition, those involved in Calvin cycle and glycolysis under ND condition were downregulated, consistent with the observation that quantum yield was reduced under ND condition. Furthermore, we showed that enzymes involved in fatty acid synthesis and glycerolipid synthesis were downregulated but not b-oxidation. Lipidomic profiling indicated that, while the level of neutral lipids in ND cells was increased compared to that of NR cells, level of photosynthetic membrane-lipids DGDG and MGDG was decreased. Taken together, our analysis indicated that TAG accumulation is attributed to the modification of membrane lipids derived primarily from “prokaryotic” pathway and secondarily from “eukaryotic” pathway based on the 16:X or 18:X fatty acid at the sn2 position of the glycerol backbone. We propose that two-phase (NR-ND) growth is ideal for biomass and biofuel production because ND reduces cell growth rate due to the loss of photosynthetic membrane and decreased quantum yield.
Project description:We report the transcriptomic dynamics and metabolic adaptation of Nannochloropsis oceanica to blue (410nm) and red (680nm) light by high-throghout Next-generation sequencing (NGS). Preferential excitation of different light spectra induces massive reprogramming of the Nannochloropsis transcriptome.
Project description:Nannochloropsis oceanica CCMP1779 is a marine unicellular stramenopile and an emerging reference species for basic research on oleogenic microalgae with biotechnological relevance. We investigated its physiology and transcriptome under light/dark cycles. We observed oscillations in lipid content and a predominance of cell division in the first half of the dark phase. Globally, more than 60% of the genes cycled in N. oceanica CCMP1779, with gene expression peaking at different times of the day. Interestingly, the phase of expression of genes involved in certain biological processes was conserved across photosynthetic lineages. Furthermore, in agreement with our physiological studies we found the processes of lipid metabolism and cell division enriched in cycling genes. For example, there was tight coordination of genes involved in the lower part of glycolysis, fatty acid synthesis and lipid production at dawn preceding lipid accumulation during the day. Our results suggest that diel lipid storage plays a key role for N. oceanica CCMP1779 growth under natural conditions making this alga a promising model to gain a basic mechanistic understanding of triacylglycerol production in photosynthetic cells. Our data will help the formulation of new hypotheses on the regulation transcriptional control of cell growth and metabolism in Nannochloropsis. Nannochloropsis oceanica CCMP was entrained to 12:12 light:dark cycles and biological replicates collected every 3 hours for a cycle for a total of 16 samples.