Optimizing The Biosynthesis Of 3-Hydroxypropionic Acid?3-HP? In Synechocystis Sp.PCC 6803

Along with intensifying of environment pollution and the expansion of the energy consumption pressure,photosynthetic cyanobacteria as "microbial cell factory" to synthesize and produce biofuels and chemicals have attracted extensive concern of the researchers.Synechocystis sp.PCC 6803,the model organism of photosynthetic cyanobacteria,has great potential for the application of biological engineering.This study is mianly about optimizing the biosynthetic pathway of 3-HP in Synechocystis sp.PCC 6803.3-hydroxypropionic acid(3-HP)is an important platform chemical and has great economic development value,so more and more researches have focused on the biosynthesis of 3-HP in recent years.In previous studies,we have constructed and optimized the biosynthetic pathway of 3-HP in Synechocystis sp.PCC 6803.However,the production of 3-HP was still very low.Based on the previous work,in this study,we further explored to improve the production of 3-HP in Synechocystis sp.PCC 6803.The strategies mainly included the following aspects: i)improving the efficiency of transferring carbon source by overexpressing the Ci transporter Bic A(Sll0834)and SbtA(Slr1512),respectively;ii)increasing photosynthesis and ATP supply by overexpressing Flv3(Sll0550)that functions as an NAD(P)H: oxygen oxidoreductase;iii)knocking out the apcE gene encoding the phycobilisome core-membrane linker polypeptide,in order to truncated light-harvesting antenna and reduce light damage;iv)directing more carbon flux into 3-HP by inactivating the competing pathways of glycogen biosynthesis;v)enhancing the supply of precursor malonyl-Co A by increasing the expression of acetyl-CoA carboxylase and biotinilase using stronger promoter.In addition,the inherent carbon fixation efficiency of cyanobacteria is relatively low,thus it is of great significance that enhancing the carbon fixation efficiency of the host cell for the optimization of cyanobacterial chassis to produce biofuels and chemicals.Ribulose-1,5-bishosphate carboxylase /oxygenase(RubisCO)is the limit enzyme of photosynthetic carbon assimilation,but its activity is very low which affects the efficiency of carbon fixation in cyanobacterial chassis.Therefore,we overexpressed three different RubisCO genes in Synechocystis sp.PCC 6803,respectively,to improve the efficiency of carbon fixation and growth rate,which may be applied to optimizing the biosynthetic pathway of 3-HP.The results showed that,the production of 3-HP was improved 26% and 10%,respectively,through the overexpression of homologous transporter BicA(Sll0834)and Flv3 protein,while other strategies did not demonstrate obvious impact,indicating that they may not be the main factors influencing the biosynthesis of 3-HP in Synechocystis sp.PCC 6803.Besides,the results showed that there were no obvious changes in the growth of chassis cell and the production of 3-HP by overexpressing RubisCO from cyanobaceria.These results suggested that enhancing the uptake ability of HCO3-and energy supply had significant effect on increasing the production of 3-HP in Synechocystis sp.PCC 6803.