Metabolic Engineering Of Cyanobacteria For Enhanced Terpene Production

The rapid economic growth in the industrial era has accompanied with a series of environmental concerns largely caused by the combustion of fossil fuels.With limited fossil fuel reserves,seeking a sustainable source of clean energy has become a top priority of our society.Cyanobacterium,a simple prokaryotic photosynthetic organism,has many advantages that other microorganism,such as E.coli lacks.Using cyanobacteria as cell factory,these photosynthetic organisms can be genetically modified to achieve carbon neutral production of biofuels,which is of great significance for solving energy crisis and air pollution problems.Limonene,a mono-terpene molecule,is an ideal candidate as aviation fuel molecules.However,the efficiency of cyanobacterial limonene production is low and is a major focus of current research field.In this study,the cyanobacterium Synechococcus elongatus PCC 7942 was used to illustrate a key limiting factor in photosynthetic terpene production.By integrating a bicarbonate transporter into the S.elongatus genome,the carbon assimilation efficiency was increased and the limonene productivity achieved 865.88 ?g/L/OD/d,which was1.3-fold higher than that of the baseline strain.This result indicated the source limitation in photosynthetic chemical production platforms.Since carbohydrate synthesis is a major carbon sink,we further deleted the glycogen synthesis pathway by knocking out and/or replacing the key enzyme AGPase gene in S.elongatus.Interestingly,the lack or attenuation of the glycogen synthesis pathway did not increase the yield of limonene,indicating a complex regulation in carbon relocation strategies in cyanobacteria.