The Regulation Of Lipid Accumulation And Transcriptome Analysis Of Eustigmato Cf. Polyphem Under Varying Nitrogen,Phosphorus,Sulfur Supply And Light Source

Microalgae play an important role in human life and has been used in livestock and poultry breeding,aquaculture,wastewater treatment,bioenergy and nutritional supplements.Eustigmatos cf.polyphem JNU-2 is a soil microalgal that belongs to Eustigmatos,Eustigmatophyceae,Heterokontophyta.Previous studies have found that JNU-2 has fast growth rate and high lipid content.The fatty acid profile shows that it is rich in palmitoleic acid and has a certain amount of EPA.So,it is a potential oleaginous microalga.In the context of these,this study investigated the growth and lipid accumulation of JNU-2 through key nutrient management and the change of light intensity and quality.And the mechanism of lipid metabolism and its related metabolic process were elucidated by transcriptome analysis.In order to explore the combined effect of three major nutrients?nitrogen-N,phosphorus-P,sulfur-S?on the growth and lipid accumulation of JNU-2,the study was designed to measure its biomass,total lipid content,fatty acid profiles and element composition under different initial N,P,S combination concentrations.Results showed that different initial N and P concentrations had significant impact on biomass and lipid content,and the effect of S on the growth was remarkable rather than lipid content.The largest biomass reached to 9.19 gL^-11 under the condition of 9 mM-NaNO₃,0.92 mM-K₂HPO₄,0.3 mM-MgSO₄.The maximum total lipid content was 68.7%of dry weight in the culture of 3 mM-NaNO₃,0.029 m M-K₂HPO₄,0.3mM-MgSO₄.The optimal culture condition for lipid productivity accumulation(0.32 g L^-1 d^-1)was 9 mM-NaNO₃,sufficient P and S concentrations.Meanwhile,we explored the physiological and biochemical characteristics of JNU-2 under different light intensities(100?mol m^-2 s^-1,300?mol m^-2 s^-1,500?mol m^-2 s^-11 and bilateral 500?mol m^-2 s^-1)and qualities?LED-blue light,LED-red light and incandescent light?including the biomass,total lipid content,fatty acid,pigment,and total carbohydrate content and protein content.Results showed that high light increased the biomass obviously,and the largest biomass was attained at bilateral 500?mol m^-2 s^-11 and 18 mM-N,which was 11.99 g L^-1.High light significantly improved the total lipid content under the condition of high N concentration,rather than low N concentration.Moreover,incandescent light and LED-red light were advantageous to the biomass and total lipid accumulation.While,LED-blue light inhibited them significantly.The relative content of?-carotene and protein was much higher under the LED-blue light compared to the culture of incandescent light and LED-red light.Finally,the transcriptome regulation of JNU-2 in different N,P,S concentrations and light intensities and qualities were studied.The results of differential gene analysis showed that under low nitrogen concentration,the specific genes related to lipid metabolism were significantly up-regulated,and the specific genes related to photosynthetic pigment protein were significantly down-regulated.Under low phosphorus concentration,there were many specific genes related to nucleotide metabolism.It indicated that the JNU2 cells had many unique response modes in this condition.Under low sulfur concentration,the number of specific genes was small,and there was no specific metabolic pathway under this condition.Under the condition of simultaneous restriction of nitrogen,phosphorus and sulfur,the specific up-regulated genes were mainly concentrated in the amino acid metabolic pathway which meant the protein metabolism changed significantly.Under high light conditions,there were lots of specific genes,which illustrated that there were many special strategies for algal cells under high light environment.These strategies were mainly related to carbohydrate metabolism.Under the condition of high light and low nitrogen,a large number of specific genes related to lipid metabolism were significantly up-regulated.Meanwhile,the specific genes associated with photosynthesis and growth were significantly down-regulated.There are a large number of specific genes under blue light conditions,among which the specific genes related to nucleotide metabolism and photosynthesis were down-regulated.It indicated that blue light conditions were not conducive to the growth of algal cells.The specific genes associated with lipid metabolism were significantly enriched,indicating the specificity of lipid metabolism under blue light conditions.Under the condition of red light,the specific genes associated with photosynthesis were significantly up-regulated,indicating that JNU-2 had a high photosynthetic capacity under this condition.According to the analysis of metabolic pathways,?1?the changes in the expression of ACCase in fatty acid synthesis were mild under different conditions.?2?The TAG synthesis under the condition of nutrient limitation were mainly dependent on DGAT,but dependent on both DGAT and PDAT under the condition of high light.Compared with incandescent light,the accumulation of TAG was decreased under blue light and red light,especially blue light;?3?the photosynthetic genes were generally down-regulated under the condition of nutrients limitation and high light,while those under the condition of blue light and red light were up-regulated,especially under the condition of red light.?4?The blue light is more favorable for the accumulation of?-carotene.?5?N metabolism-related genes were significantly up-regulated under blue light which indicated that N metabolism was active under this condition.?6?The ability of JNU-2 to absorb exogenous S was decreased under the condition of low N and P concentration but remained at a certain level under low S concentration,meanwhile,the efficiency of utilizing endogenous S was enhancement.This study optimized the nutrition and light conditions for the growth and lipid accumulation of JNU-2,which provided the scientific and effective theoretical data to the large-scale production of this alga.At the same time,the mechanism of metabolism and lipid accumulation of this alga were analyzed by the means of transcriptional analysis,which offered an important academic basis to its further study of molecular biology.