| With the increasing demand for energy and industrial products,the bio-economy of replacing traditional chemicals with bio-based products has attracted much attention.The development of genomics and synthetic biology makes the use of recombinant microorganisms to produce bioplastics,biofuels and other bio-based products have good prospects.PHA is fully bio-synthesized bioplastic with good biocompatibility and degradability.The physical properties of polyester plastics can be changed by changing the type and ratio of monomers.Therefore,the research on the production of polyester bioplastics mixed with different monomers by metabolic transformation is currently a hot topic.As an important part of fossil fuels,hydrocarbon compounds are generally extracted from crude oil,but the research on the use of microorganisms to synthesize fatty hydrocarbons also provides new ideas for replacing fossil fuels.Using lignocellulosic raw materials to produce PHB and aliphatic hydrocarbons is conducive to reducing production costs and saving food resources.However,there are few reports on the production of PHB and hydrocarbons from cellulosic raw materials,because many strains are not suitable for lignocellulose systems.Dry biorefinery process by our laboratory can effectively utilize the fermentable sugar in lignocellulose,and Corynebacterium glutamicum S9114 has a good adaptability to the inhibitors in this system,and has been used in glutamic acid fermentation.In this study,it was used as a starting strain for transformation,using metabolic engineering to introduce PHB and aliphatic hydrocarbon synthesis pathways,and successfully achieved the synthesis of products,which is conducive to further promoting the industrial production of bioplastics and biofuels.In the first part of this study,C.glutamicum S9114-ΔldhA1::xylAB was used as the starting strain,and PHB was successfully synthesized using the PHB synthesis pathway from Ralstonia eutropha H16.The present study also attempted metabolic modification by increasing the supply of substrate acetyl-coa and strengthening anabolism,and found that overexpression of synthetic pathway genes can increase the PHB content to twice.In addition,it was found in the study that the expression of gene phaP,a helper gene for PHB synthesis,had the best effect,and finally obtained a PHB content of 19.51%and a PHB yield of 2.36 g/L.The second part of this study is the transformation of C.glutamicum S9114’s hydrocarbon production metabolism.Hydrocarbon-producing strain HW4 was obtained by introducing the aliphatic hydrocarbon synthesis route from Synechococcus elongatus PCC7942.The fermentation broth products were C21-C30 long-chain hydrocarbons and many of fatty acids.The total hydrocarbon production measured by fermentation was 18.77 mg/L.This study speculate that the long-chain hydrocarbon synthesis mechanism is related to fatty acid metabolism and mycobacterial acid metabolism,and use qRT-PCR to analyze the expression of related genes.Many fatty acids affect product extraction and detection,so study introduced fatty acid decarboxylase OIeTJE,OleTMC genes,consumed accumulated fatty acids and obtained C12-C17 long-chain olefins.This study obtained the JH01 strain capable of synthesizing PHB and the HW4 strain capable of producing aliphatic hydrocarbons,and increased product yield through metabolic engineering.The study on the mechanism of improving PHB production and very-long-chain hydrocarbons provides new ideas for further production stimulation. |
