Studies Of Metabolic Engineering Of Typical Terpenoids In Cyanobacteria Biofuels

Continuous growth of human population and industrialization lead to increased energy demands all over the world,biofuels were attract widespread attention as substitutes of traditional fuels,are renewable,biodegradable and environmental friendly.As of now,the United States and other developed countries and regions for biofuel attention and research results are far ahead of China,and the main research direction is through photosynthetic microorganisms to produce biofuels and high-value products.Among them,cyanobacteria has great application prospects as an important feedstock for the third generation biofuels,which use of sunlight as energy resource and convert CO2 into various forms of bioenergy.A wide variety of terpenoids not only can be used as a substitute for traditional fuels,but also the application of a wide range of high-value compounds.Therefore,to harness cyanobacteria as a metabolic platform for the production of terpenoids is the focus of this field,however at this stage of domestic research on this part is still blank.In this paper,cyanobacteria as an experimental subject,base on the common use methods in metabolic engineering and understanding of it's MEP pathway,the highly efficient exogenous key terpene synthase gene(limonene synthesis gene and farnesene synthase gene)was expressed in Cyanobacterium Synechococcus elongatus PCC7942 and we verify the accumulate amount of squalene in Synechocystis sp.PCC 6803AShc,in order to explore its impacts on cyanobacteria's production of different terpenes which including monoterpene-limonene,sesquiterpene-farnesene,triterpene-squalene.And the main findings are as follows:1.By constructing a plasmid containing the limonene synthase gene and expressing the LS gene successfully,we demonstrated that the limonene synthase gene is the key to the synthesis of limonene and Cyanobacterium Synechococcus elongatus PCC7942 has the ability to produce limonene.And the expression of the same gene was affected by different promoters.The yield of the strain which containing Ptrc promoter and RBS reached the highest daily yield of 53.0 ?g/L/OD/day.Therefore,it was necessary to select the efficient promoter to increase the yield.2.By constructing a plasmid containing the Famesene synthase gene and expressing the FS gene successfully,we have demonstrated that the Famesene synthase gene is the key to the synthesis of Famesene,and cyanobacterium PCC7942 also has the esscential raw materials and enzymes in the synthetic pathway.3.The results showed that the knot out the Shc gene which at the downstream of squalene synthease was able to accumulate squalene,and the yield of squalene Synechocystis sp.PCC6803?Shc reached 2.48mg/L/OD,and on the basis of mutant by metabolic engineering to further improve the production of squalene,squalene synthesis gene may be an breakthrough.4.The results showed that cyanobacteria could produce different kinds of terpenes including monoterpenes,sesquiterpenes and triterpenes,and cyanobacteria as prokaryotic photosynthetic autotrophic microbes had many advantages,which could be used to product terpenes and achieve more objective yield through genetic modification.Which provides the possibility of industrial production of cyanobacteria biofuels.