Enhanced Lipid Accumulation Mechanism In Chlorella Cells Under Salt-stress

The concept of using oil-rich microalgae biomass as feedstock for biodiesel production has been explored over the past few decades. However, little information is available on the mechanisms directly or indirectly associated with algal lipid biosynthesis. Therefore, revealing the regulation of lipid metabolism and interaction mechanism of environment was especially vital to enhance lipid accumulation. The paper investigated the lipid accumulation and metabolic pathway of Chlorella vulgaris salt-stress inuction. The main contents and results were as follows: 1. Study on the effects of NaCl-stress on the lipid content of C. vulgarisC. vulgaris was cultivated heterotrophically to achieve a biomass of 7.8 g/L in the initial 5 days. The collected heterotrophic cells were re-suspended into fresh media supplemented with 0.5 M NaCl followed by 12 h growth to accumulate the lipid content of 53.4%.The lipid productivity(625.3 mg/L/d) achieved with heterotrophic-Na+ induction was better than that using heterotrophy alone(404.6 mg/L/d). 2. Study on the effects of KCl-stress on the lipid accumulation of C. vulgarisC. vulgaris was cultivated heterotrophically then re-suspended into fresh media supplemented with KCl followed by 12 h growth to accumulate the optimized biomass and lipid content by 7.27 g/L and 42.9%.The lipid productivity(623.8 mg/L/d) achieved with heterotrophic-K+ induction was better than that using heterotrophy alone(404.6 mg/L/d). 3. Study on the effects of different combination of sodium potassium concentration on lipid accumulation of C. vulgarisThe regression equation obtained by Design-Expert analysis of process parameters of sodium potassium influencing Chlorella vulgaris lipid content was as follows: Y=43.22+2.59*A+2.59*B-8.28*A*B-9.98*A*C-7.06*B*C-10.21* C2(A: Potassium concentration; B: Sodium concentration; C: Time).R2 equals 0.945. The optimum condition: incubation time 38.86h; potassium concentration 0.40mol/L, sodium concentration 0.42mol/L, the oil content under these conditions was 48.51%, and the predicted value(48.39%) are basically the same(relative tolerance is only 0.24%), the equation fit the actual situation more accurately. 4. Lipid accumulation mechanism of salt-stress by proteomicsA representative oleaginous Chlorella vulgaris was tested to reveal the regulation of lipid metabolism response to NaCl-stress stimulation. Several pathways, such as starch metabolism, glycolysis, TCA cycle, glyoxylate cycle, fatty acid synthesis, TAG metabolism, protein synthesis and folding were directly related to lipid synthesis. The lipid biosynthesis process was probably fulfilled by the cooperation of many organelles, such as ER, mitochondrion, chloroplast, cytosol, and plasma membrane. Additionally, transport and regulate, ROS scavenging defense systems were indirectly involved in the complex processes.