The Study Of The Photophosphorylation Uncoupler Promoting The Growth And Lipid Accumulation Of Chlorella

The exhaustion of non-renewable energy resources on the earth has initiated researchers to explore novel and alternative energy sources.The biodiesel produced from microalage lipid transesterification is one of the promising green technologies for the production of biofuel.The microalgae grow fast,easy to cultivate and accumulate high content of triacylglycerols(TAGs),which is an important raw material for the production of biodiesel.The key to solve the problem of high feedstock cost is to obtain fine algae and suitable culture conditions to promote the lipid accumulation of microalgae.In this study,we used photophosphorylation uncoupler to promote the growth and lipid accumulation of Chlorella,and revealed the mechanism by applying comparative transcriptome and qPCR.The contents of this paper include the following aspects:1.We studied the growth and lipid accumulation of Chlorella,Chlamydomonas reinhardtii,Scenedesmus obliquus and Scenedesmus Dunaliella growing in different carbon sources.The Chlorella was concluded to have the fastest growth rate and the highest lipid accumulation,and the results showed that the optimum conditions for the mixotrophic cultivation of Chlorella were under 0.5 mM nitrate and 50 mM sodium acetate,resulting in the lipid productions were significantly higher than they growing in BG11.And we studied the effect of photophosphorylation uncouplers CCCP and FCCP on the growth and lipid accumulation of Chlorella.The results showed that addition of 1 μM CCCP or FCCP improved the growth and lipid accumulation of Chlorella F4,compared with the same conditions without photophosphorylation uncoupler,the biomass was increased by 8.11%,neutral lipid content was increased by 19.67% under the addition of 1 μM CCCP;and the biomass was increased by 7.37%,neutral lipid content was increased by 22.40% under the addition of 1 μM CCCP.2.We studied the mechanism of photophosphorylation uncoupler on promoting the microalgae growth and lipid accumulation by comparing the transcriptome of Chlorella growing mixotrophically.The results showed that mixotrophic cultivation of Chlorella with 1 μM CCCP or FCCP,the gene expression of Cyt b6,photosystem II oxygen-evolving enhancer protein and plastocyanin in the photosynthesis pathway was increased,and the gene expression of lipid synthesis pathway was increased,the gene expression of lipid degredation pathway was decreased,indicating that the enhancement of Photosynthesis and the synthesis NADPH,resulting in promoting the lipid accumulation of Chlorella F4.The overall up regulation of Calvin cycle and TCA cycle gene was consistent with its apparent growth rate.3.In order to more accurately and deeply understand the mechanism of photophosphorylation uncoupler to promote the growth and lipid accumulation of Chlorella,the expression of central metabolic gene based on qPCR was analyzed.According to the results of qPCR,mixotrophic cultivation of Chlorella with 1 μM CCCP or FCCP,The gene expression of F-ATPase in the pathway of photosynthesis was decreased,but the gene expression of some components related to electronic delivery such as membrane protein D1,Cyt B6 and ferredoxin--NADP+ reductase were increased,the gene expression of lipid synthesis pathway was increased,the gene expression of lipid degredation pathway was decreased,it showed that photophosphorylation uncoupler eliminated the proton gradient of the transmembrane,reducing the reverse inhibition of proton gradient to photosynthesis and improving the overall photosynthetic efficiency,resulting in electrons were transferred to the NADP reductase along the photosynthetic electron transfer chain and promoting the accumulation of NADPH and eventually promoting the synthesis of lipid.In addition,the gene expression of Calvin cycle and TCA cycle were increased,which consisted with the results of transcriptome.