Lipid Metabolism Research Of Chlorella Vulgaris Under Nitrogen Limited Condition

Due to the limited stocks of fossil fuels and the increasing emission of greenhouse gas carbon dioxide into the atmosphere from the combustion of fossil fuels, research has begun to focus on alternative biomass-derived fuels. Microalgae, which has higher biomass production and faster growth than those of other energy crops, has attracted a lot of attention as a potential source of biofuel. To exploit indigenous microalgal species with the potential for biodiesel production, algal cultures were isolated from seawaters around Hainan university, and one algae was identified based on its high lipid content. The research result showed the algae grew rapidly and promoted the accumulation of oil. Ribosomal small-subunit18sRNA gene sequence of the algae was cloned and then the phylogenetic trees (Neighbor Jointing and Maximum Likelihood) were constructed based on18S rRNA sequence of the algae as well as other species were obtained from the GenBank database. These results revealed this algae was one of Chlorella vulgaris.In this study we used Chlorella vulgaris as a reference organism for analysis C and N contents of the N starvation response in algae. At same time, change of nitrate nitrogen and total nitrogen in medium was tested. The result showed N content reduced obviously under nitrogen deprivation and the content of total carbon had no significant changes between the two treatments. Consumption of nitrate nitrogen and total nitrogen in medium were in accord with growth of Chlorella vulgaris. In order to explore the mechanisms improving lipid productivity of Chlorella vulgaris under nitrogen-depleted (N-), metabolomic strategy using GC-TOF/MS was employed to systematically study the metabolites differences of Chlorella vulgaris under the N-and N+condition. The result indicated a total of768metabolites were identified in Chlorella vulgaris, and significant changes in the metabolites existed between N-and N+group. Metabolites involved in fatty acid synthesis, glycolytic pathway and the citric acid cycle were up-regulated under nitrogen deficiency condition, and N deprivation triggered protein and amino acid degradation. The identified differential metabolites and related pathways may give a preliminary explanation to oil accumulation of Chlorella vulgaris under under nitrogen deficiency condition.Studies on the utilization of algae as biofuels often require frequent determinations of algal lipid content. In this study, we used three staining methods (Nile red, Sudan Black B and Oil Red O dye methods) for quantification the relative lipid levels in various stage strains of Chlorella vulgaris. The results showed that there was a linear correlation between the lipids level and the light absorb value of stained microalgal cells. The content of microalgal cell lipids (y) is related to the absorbance(x) of cells and can be expressed with a regression equation of the form y=kx+b. The regression equation of Nile red method was y=0.009543x+3.087(fluorescence value at580nm), and the correlation coefficient (R2) was0.9577(P<0.001).For Sudan Black B method, the equation was y=30.06x+3.705(optical density at645nm), and R2is0.9603(P<0.001). In Oil Red O dye manner, the regression equation was y=72.83x-27.87(optical density at600nrn), and R2was0.8878(P<0.005), but optical density at600nm ranged only within0.4-0.6. These results indicated that three staining strategies were suitable to estimate the lipid content of Chlorella vulgaris cells.