Study On Photosynthetic Biosynthesis Of Ethanol In Genetically Engineered Cyanobacteria

With the continuous development of the world economy,energy shortage and environmental pollution problems have gradually emerged,it is essential to develop a sustainable,clean energy and relieving environmental pollution.Cyanobacteria,photoautotrophic microorganisms,can convert carbon dioxide to organics,and release oxygen through photosynthesis.Utilizing cyanobacteria to synthesize biofuels can not only ease energy shortage,but also reduce the greenhouse effect by recycling the carbon dioxide of combusting fossil fuels.In this study,we explore the optimization strategy to synthesize bioethanol through cyanobacteria's metabolic pathway and genetic engineering,the main research content and results are as follows:Firstly,a Synechocystis sp.PCC6803 single copy strain Syn-ZG25 which expressed the pyruvate decarboxylase gene(PDCzm)from Zymomonas and alcohol dehydrogenase gene(slr1192)from Synechocystis PCC 6803 in the slr0168 genomic site,we are on the basis of Syn-ZG25 and overexpress a PDCzm gene in pha AB site called Syn-YQ4.Interestingly,the ethanol productions of Syn-YQ4 and double copy strains Syn-HZ24 are considerable,and the Syn-HZ24 was constructed by genetically introducing PDCzm and slr1192 gene at slr0168 and pha AB site.Then the results of enzyme activity and Western Blot indicate that PDCzm is the limiting factor in the producing ethanol pathway.Secondly,the ethanol producing strains of Synecoccus sp.PCC 7002 in Western Blot experiment show the slr1192 expression was significantly higher than PDCzm,then we use the strong promoter to control slr1192 in the wild type and oxerexpress a slr1192 in ethanol producing strain.The formely method is invalid and the latter improves enzyme activity and expression amount of slr1192.Thirdly,Synechococcus elongates UTEX 2973 was the fateset growing cyanobacteria reported up to now.We introduce the exogenous PDCzm and slr1192 gene through homologous recombination at neural site NS1,the gene was inserted from the forward(Syn-YQ16)and backward(Syn-YQ17)respectively.Syn-YQ16 can produce more ethanol than Syn-YQ17 in the same fermentation conditions,however the rate of ethanol synthesis was lower compared with PCC 6803 and PCC 7002.