Analysis Of Starch And Lipid Contents And Transcriptomic Profiles In Chlorella Sp.G32 Upon Changes Of Glucose Concentrations

Chlorella is of high economic value with abundant protein content and excellent ability of lipid and starch synthesis.Under autotrophic condition,Chlorella was demonstrated low cell density and high cost-recovering.Nevertheless,metabolic regulation on starch and lipid synthesis in chlorella cells still remain unclear.This study aims to analyze the cell biomass and biomacromolecule productions of Chlorella sp.G32 under different glucose concentrations and clarify the key enzymes of regulating starch and lipid metabolisms at the genome level.In this study,the maximum biomass of Chlorella G32 in 2×BBM medium(containing 1.25 g/L glucose)and 2×BBM medium(containing 5 g/L glucose)reached(0.83±0.05)g/L and(2.63±0.10)g/L(p=2.57×10-5),respectively.Chlorella G32 could synthesize more lipid and starch under 2×BBM medium under high glucose condition,whereas the ratio of lipid content to cell dry weight under high glucose was slightly lower.Furthermore,after cultured in 2×BBM medium with high and low glucose for adaption separately,G32 were transferred to low and high glucose,respectively.Transcriptome sequencing was used to analyze differential expressed genes in those above conditions.Under high glucose,the expression level of key enzymes involved in starch synthesis pathway was up-regulated overall,where enzymes synthesizing starch was up-regulated,whereas enzymes synthesizing fructose was down-regulated,resulting in accumulating more starch under high glucose concentration.The main flow of glycerolipid metabolism at high glucose concentration was to synthesize fatty acid.Key enzymes in TAG decomposition pathway was found up-regulated and the ratio of lipid content to cell dry weight was decreased under high glucose.In summary,this study compared key enzymes in lipid and starch metabolic pathways in Chlorella G32 through transcriptome level,which will contribute to the subsequent genetic modification of Chlorella G32.By inhibiting the activity or expression level of the key enzymes in starch and lipids metabolic pathways,the production of high-value products may be improved,thus creating great economic benefits.