Modification Of Metabolic System To Synthesis 3,4-dihydroxybutyric Acid From Xylose By Engineered Escherichia Coli

3,4-dihydroxybutyric acid(3,4-DHBA),a versatile platform four carbon(C4)chemical,is used as a precursor during the production of many commercially important chemicals or synthesis of antibiotics,?-and ?-amino acids and peptides.The chemical synthesis of 3,4-DHBA mainly comes from the saponification of its lactone form 3-hydroxy-?-butyrolactone(3HBL).Therefore,biosynthesis will be the main method for 3,4-DHBA synthesis in the future.Here we reported the first biosynthetic pathway towards 3,4-DHBA in recombinant Escherichia coli using xylose as feedstock to synthesize the target substance and glucose is used for cell growth.The pathway mainly consists of a four-step reaction,including xylose dehydrogenate catalyzed by xdh,xylonate dehydratase catalyzed by yjhG / yagF of Escherichia coli itself,mdlC catalyzed decarboxylation of 2-keto-3-deoxy-oxopentanone and the last step catalyzed by aldehyde dehydrogenase(ALDH)which can oxidation of 3,4-dihydroxybutanal to produces 3,4-dihydroxybutyric acid.We first attenuated the synthesis of BT,and than overexpression of ALDH to construct the synthesis pathway of 3,4-DHBA,achieving a major breakthrough in production from scratch.In addition,xylD from Caulobacter crescentus was overexpressed and yiaE was knocked out to make more of the carbon source flows to the final product.Simultaneously,the dual-gene co-expression strategy not only increases yield,but also proved that the last step is a rate-limiting step.Also,deletion of methylglyoxal synthase gene(mgsA)increased xylose and glucose co-metabolism and overexpressed water-forming NADH oxidase(NoxE)from Lactococcus lactis to restore the redox cofactor imbalance,resulting in an improvement of 3,4-DHBA production by 30%.Finally,the strategies of these approaches led to 3,4-DHBA production of 0.38 g/L.In summary,This study proposed a new method for biosynthesis of 3,4-DHBA from renewable lignocellulosic biomass and made the basis for subsequent research.