Study On Transcription Differences Of Carbon And Nitrogen Metabolisms Related Lipid Synthesis And Lipid Synthesis Of Chlorella Vulgaris

Chlorella vulgaris was used as a model of oil producing algea to research the effection ofnitrogen resource and the concentration on algal oil accumulation. The transcriptionaldifferences of carbon and nitrogen metabolic genes in the oil synthesis pathway werediscovered at different cultivation conditions. By analysis of the relations between thetranscriptional differences and the oil accumulation, some of the critical precursors and TCAinhibitors were added to increase the oil synthesis.It was found that NaNO3was an optimal nitrogen source for Chlorella vulgaris tosysthesize fatty acids. The optimal concentration of NaNO3for oil accumulation formC.vulgaris C95was also studied. The effects of the oil accumulation were compared undernitrogen cultivation and deficient nitrogen cultivation. The results showed that while0.8g·L-1NaNO was added to the medium for cultivateing C.vulgaris C95, the biomass yield andaverage growth rate were338.4mg·L-1and27.90mg·L-1·d-1, respectively, and the oil contentand oil yield were12.01%and4.55mg·L-1·d-1. The highest biomass and oil content reached to626.3mg·L-1and11.68%under nitrogen cultivation, and332.8mg·L-1and13.49%undernitrogen-deficient cultivation. The oil accumulation under deficient nitrogen cultivation washighest, which was improved by15.5%compared to the nitrogen cultivation.The carbon and nitrogen metabolism genes associated with lipid synthesis at threecultivation periods were detected by fluorescent quantitative PCR. The obviously changes oftranscriptional level were found from the genes of gapA, accD, mdh, Me, GSII and PII,between4days cultivation under nitrogen procedure and4days cultivation under nitrogendeficient process. Most of the above genes are carbon metabolic related. The genetranscription levels of gapA, accD, mdh and Me of4days under deficient nitrogen cultivation,were13.9,24.8,6.6and17.1folds higher than that from the samples of4days under nitrogencultivation, respectively. The results indicated that the gene of gapA, accD, mdh and Meplayed important roles in Chlorella vulgaris lipid accumulation. Hence it might imply that thepromption of gapA, accD, mdh and Me transcription and expression would improve lipidsysythesis by C.vulgaris C95.Furthermore, some of the metabolic intermediates and inhibitors were chosen to enhancethe transcritional levels of related genes. It was found that adding of citric acid, salicylic acid,potassium iodide and malonic acid help promote the accumulation of algal lipid, whencultivating initiated under nitrogen deficiency condition. The lipid content was raised to14.21%,14.52%,15.32%and14.14%, compared with the levels of control groups as10.6%,15.2%,21.6%and28.3%, respectively. When adding sodium acetate, hydrogen peroxide, andmalonic acid after2days cultivation under nitrogen deficiency, the comtents of algal lipidwere promoted to15.09%,16.9%and16.17%, respectively, about17.4%,34.1%and17.4%higher than that of the control groups. When adding a mixture of sodium acetate andpotassium iodide, as metabolic intermediates and TCA cycle inhibitors, under initial nitrogendeficiency condition, the lipid content increased up to27.24%, as1.96folds of the controlgroup. Meanwhile, adding the same mixture of sodium acetate and malonic acid under nitrogen deficiency condition started after2days cultivation, the lipid content increased up to28.6%, as2.22folds of the control group. It might be a new protocal of adding small amountof metabolic intermediates and TCA inhibitors to enhance the Cholrella lipid accumulationand promote the algal oil production.