Lipid Accumulation And Regulation Mechanisms Of Chlorella Protothecoides With Combination Cultivation Mode Of Nitrogen Deficiency And Phosphorus Repletion

Effect of nitrogen and phosphorus synergistic induction mode(namely N+-P+,co-repletion of N and P, the control group; N--P+, N-deficiency and P-repletion; N+-P-,N-repletion and P-deficiency; N--P-, co-deficiency of N and P; N--P-lim, N-deficiency and P-limitation) on biomass and lipid accumulation of C. protothecoides were implemented, as well as the regulation mechanisms of lipid accumulation under the optimal nitrogen and phosphorus synergistic induction mode. Results showed that the maximal biomass was 5.92 g/L under co-repletion mode of N and P, which is higher than N-deficiency and P-repletion mode(2.99 g/L), N-repletion and P-deficiency mode(2.38 g/L), N-deficiency and P-deficiency mode(0.76 g/L), as well as the N-deficiency and P-limtation mode(2.81 g/L). The maximal lipid content was 55.8%under co-deficiency mode of N and P, which is higher than control group(22.17%),N-deficiency and P-repletion mode(52.5%), N-repletion and P-deficiency mode(32.77%), as well as the N-deficiency and P-limtation mode(53.7%). However, the maximal lipid productivity appeared in N-deficiency and P-repletion mode, which reached by 224.14 mg/L/d, representing 1.19-3.70 times more than that of control,N-depletion and P-deficiency mode, co-deficiency of N and P mode as well as N-deficiency and P-limitation mode respectively. The phenomenon indicates that the N-deprivation and P-repletion synergistic induction mode was of potential to lead to lipid accumulation in C. protothecoides.Furthermore, regulation mechanisms corresponding with lipid accumulation under N-deficiency and P-repletion were also elucidated by proteomics based on DIGE measure. There were 27 significantly varied protein spots. The proteins identified under N-deficiency and P-repletion mode included 8 up regulated and 19 down regulated ones. According to the metabolism pathway analysis, up-regulated UDP-glucose-6-dehydrogenase and glucose-1-phosphate adenylyltransferase participated in glycolysis were key factors for lipid accumulation under N-deficiency and P-repletion mode. The two enzyme were responsible for catalyzing starch, which was stored as the primary carbon in C. Protothecoides cells, into glucose to provide one entry point for the glycolysis pathway. The pentose phosphate pathway(PPP), in which the up-regulated transketolase transformed 5-carbon ketose and 5-carbon aldose to form 7-carbon ketose and glyceraldehyde-3-P(G3P). Moreover, the up-regulated ribulose bisphosphate carboxylase(RuBisCO) large chain was keyenzyme for promoting calvin cycle which contributes 3-phosphate dehydrogenase(G3P) into glycolysis pathway. The up-regulated malate dehyrogenase were benificial to lipid accumulation, which was the basis of predicting key regulatory factors for lipid accumulation pathway. Nitrate reductase(NR), which was the nitrogen signal regulating factor, was regarded as potential site of control for lipid biosynthesis. The up-regulated glutamate dehydrogenase(GLDH) may help C. protothecoides cells against nutrient imbalance stress. These results provide the foundation to develop engineering strategies targeting lipid accumulaiton and advance microalgae-based biodiesel productivity for industrial production as well as render a reference for other microalgae.