Efficient one-step production of γ-aminobutyric acid from glucose without an exogenous cofactor pyridoxal-5′-phosphate was realized by the designedCorynebacterium glutamicum.
1,3-Propanediol (1,3-PD) has versatile applications in polymers, cosmetics, foods and medicines. In order to consolidate the functions of glycerol dehydratase genedhaB and 1,3-propanediol oxidoreductase gene dhaT and produce 1,3-PD from glycerol, the genes dhaB and dhaT from Klebsiella pneumoniae were inserted into a co-expression vector pACYCDuet-1 synchronously and the recombinant strain E. coli/pACYCDuet-dhaB-dhaT was obtained. Both enzymes were functionally co-expressed in E. coli at the presence of the selective pressure and the addition of the IPTG. The specific enzyme activity of DHAB and DHAT were 8.3 and 6.2 U/mg, respectively. When cultivated at 37°C for 30 h, the recombinant microorganisms produced 1,3-PD of 11.3 g with the consumption of 40 g glycerol per liter. The production of 1,3-PD by the strain E. coli/pACYCDuet-dhaB-dhaT was about 13-fold higher than the recombinant E. coli harboring the gene dhaB.
Key words: 1,3-propanediol, Klebsiella pneumoniae, co-expression system, T7RNA polymerase promoter.
1,3-Propanediol is one of the most important industrial chemicals for its highly desired properties and its wide applications as a key component of an emerging polymer business. Biological production of 1,3-propanediol has been a novel and competitive way. In our previous job, the gene dahB encoding for glycerol dehydratase from Klebsiella and the gene yqhD encoding for 1,3-propanediol oxidoreductase isoenzyme from E. coli were cloned respectively. The two genes were then tandemly ligated and expressed successfully in E. coli. The recombinant E. coli strain could produce 1,3-propanediol from D-glycerol. In the current research, the expression vectors including pGAPZB-yqhD, pGAPZB-dhaB and pYX212-zeocin-pGAP-yqhD-pGAP-dhaB were furtherly constructed on the basis of our previous job. Then the vector pYX212-zeocin-pGAP-yqhD-pGAP-dhaB was introduced into Saccharomyces cerevisiae W303-1A using LiAc transformation method successfully. D-glucose is used as substrate to produce 1,3-propanediol with the recombinant strain after fermentation for 72h. SDS-PAGE analysis showed recombinant products at about 61kD, 43kD, 21kD, 15kD, consistent with the molecular weight from the report. The specific enzymatic activity of the glycerol dehydratase and 1,3-propanediol oxidoreductase isoenzyme of the recombinant yeast strain S. cerevisiae W303-1A/pYX2l2-zeocin-pGAP-yqhD-pGAP-dhaB were 24U/mg protein and 15U/mg protein, respectively, while those of the control were undetectable. In contrast to the wild strain without 1,3-propanediol output, 1,3-propanediol concentration of the recombinant yeast strain S. cerevisiae W303-1A/pYX212-zeocin-pGAP-yqhD-pGAP-dhaB reaches about 1.5g/L. The above results showed that the engineered S. cerevisiae strain which can convert the D-glucose as substrate to produce 1,3-propanediol by one-step fermentation was constructed successfully. This accomplishment bodes well for future construction of recombinant yeast strain which could overproduce 1,3-propanediol with the lower cost feedstock D-glucose by introducing the two genes yqhD and dhaB into the yeast strain overproducing glycerol with D-glucose (e.g. Candida glycerinogenes WL2002-5, which is capable of producing glycerol more than 120g/L with D-glucose as substrate and has been used for the commercial production of glycerol).
D-mannose is a natural hexose with great economic and application values in the food, medicine, and cosmetic fields. However, most biosynthesis methods of D-mannose rely on
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)