Proteomic Analysis On Chlorella Vulgaris Under Different Iron Concentrations

Due to its photosynthesis efficiency, high growth rate, and photosynthetic machinery and metabolic pathways similar to higher plants, Chlorella has long been used as a model organism to understand photosynthesis in higher plants. Photoautotrophic is referred to the cells that harvest light energy convert into chemical energy by photosynthetic reaction, and assimilate CO₂ as a carbon source, and inorganic carbon can be assimilated for carbohydrate synthesis. The cost of photoautotrophic culture is low. Mixtrophic is referred to cells that rely on photosynthesis as the main energy source, meanwhile, both organic components and CO₂ are required. Mixtrophic culture could compensate for the low bimass of autotrophic culture, and receive a rapid growth of biomass with shortening culture time.The growth rate of Chlorella was promoted by iron, previous studies showed that oil accumulation of Chlorella was also improved by high concentration iron. This research investigated the lipid accumulation process of freshwater Chlorella vulgaris under different iron concentrations conditions（low iron concentration 0, middle iron concentration 1.2×10-6, hign iron concentration 1.2×10-5 mol·L-1） and proteomics was used to explain the response mechanism of C. vulgaris to iron.In this research, the growth rate and neutral lipid content of autotrophic C. vulgaris were determined under different iron concentrations. Cells in late growth phase were collected by centrifugation and protein was extracted for proteomic analysis. When cultured photoautotrophicly, the neutral lipid content of C. vulgaris was highest under iron deficiency condition and the growth rate was slowest and biomass was lowest. Proteomics analysis revealed that C. vulgaris which was cultured under low and high iron concentrations conditions were in stress, the function of PSI and PS II impaired, the rate of electron transport and carbon fixation declined, and carbohydrate metabolism related proteins decreased. Proteins which were related to resistance increased under iron-deficiency and iron-replete conditions, but stress under iron-deficiency condition was more serious. Results showed that the growth rate of mixtrophic C. vulgaris was faster than that of autotrophic, and the content of neutral lipid was higher in mixtrophic culture than that in autotrophic condition. This maybe due to the algae could use acetate directly to convert into acteyl CoA, when under iron-deficiency condition acteyl CoA influxed into fatty acid synthesis pathway to synthesize large amounts of neutral lipids. When under iron-replete condition acteyl CoA influxed into tricarboxylic acid cycle pathway to accelerate respiration rate. Acetate was directed used by algae cells which was faster than carbon fixation cultured photoautotrophic. The content of proteins related tricarboxylic acid cycle pathway were increased under iron-deficiency condition and growth rate was promoted.