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Production of a novel quercetin glycoside through metabolic engineering of Escherichia coli.

ABSTRACT: Most flavonoids exist as sugar conjugates. Naturally occurring flavonoid sugar conjugates include glucose, galactose, glucuronide, rhamnose, xylose, and arabinose. These flavonoid glycosides have diverse physiological activities, depending on the type of sugar attached. To synthesize an unnatural flavonoid glycoside, Actinobacillus actinomycetemcomitans gene tll (encoding dTDP-6-deoxy-L-lyxo-4-hexulose reductase, which converts the endogenous nucleotide sugar dTDP-4-dehydro-6-deoxy-L-mannose to dTDP-6-deoxytalose) was introduced into Escherichia coli. In addition, nucleotide-sugar dependent glycosyltransferases (UGTs) were screened to find a UGT that could use dTDP-6-deoxytalose. Supplementation of this engineered strain of E. coli with quercetin resulted in the production of quercetin-3-O-(6-deoxytalose). To increase the production of quercetin 3-O-(6-deoxytalose) by increasing the supplement of dTDP-6-deoxytalose in E. coli, we engineered nucleotide biosynthetic genes of E. coli, such as galU (UTP-glucose 1-phosphate uridyltransferase), rffA (dTDP-4-oxo-6-deoxy-d-glucose transaminase), and/or rfbD (dTDP-4-dehydrorahmnose reductase). The engineered E. coli strain produced approximately 98 mg of quercetin 3-O-(6-deoxytalose)/liter, which is 7-fold more than that produced by the wild-type strain, and the by-products, quercetin 3-O-glucose and quercetin 3-O-rhamnose, were also significantly reduced.

SUBMITTER: Yoon JA

PROVIDER: S-EPMC3370505 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Production of a novel quercetin glycoside through metabolic engineering of Escherichia coli.

Yoon Jeong-A JA Kim Bong-Gyu BG Lee Woo Ju WJ Lim Yoongho Y Chong Youhoon Y Ahn Joong-Hoon JH

Applied and environmental microbiology 20120406 12

Most flavonoids exist as sugar conjugates. Naturally occurring flavonoid sugar conjugates include glucose, galactose, glucuronide, rhamnose, xylose, and arabinose. These flavonoid glycosides have diverse physiological activities, depending on the type of sugar attached. To synthesize an unnatural flavonoid glycoside, Actinobacillus actinomycetemcomitans gene tll (encoding dTDP-6-deoxy-L-lyxo-4-hexulose reductase, which converts the endogenous nucleotide sugar dTDP-4-dehydro-6-deoxy-L-mannose to ...[more]

PMID: 22492444

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Project description:BACKGROUND:The biosynthesis of high value-added compounds using metabolically engineered strains has received wide attention in recent years. Myo-inositol (inositol), an important compound in the pharmaceutics, cosmetics and food industries, is usually produced from phytate via a harsh set of chemical reactions. Recombinant Escherichia coli strains have been constructed by metabolic engineering strategies to produce inositol, but with a low yield. The proper distribution of carbon flux between cell growth and inositol production is a major challenge for constructing an efficient inositol-synthesis pathway in bacteria. Construction of metabolically engineered E. coli strains with high stoichiometric yield of inositol is desirable. RESULTS:In the present study, we designed an inositol-synthesis pathway from glucose with a theoretical stoichiometric yield of 1 mol inositol/mol glucose. Recombinant E. coli strains with high stoichiometric yield (>?0.7 mol inositol/mol glucose) were obtained. Inositol was successfully biosynthesized after introducing two crucial enzymes: inositol-3-phosphate synthase (IPS) from Trypanosoma brucei, and inositol monophosphatase (IMP) from E. coli. Based on starting strains E. coli BW25113 (wild-type) and SG104 (?ptsG::glk, ?galR::zglf, ?poxB::acs), a series of engineered strains for inositol production was constructed by deleting the key genes pgi, pfkA and pykF. Plasmid-based expression systems for IPS and IMP were optimized, and expression of the gene zwf was regulated to enhance the stoichiometric yield of inositol. The highest stoichiometric yield (0.96 mol inositol/mol glucose) was achieved from recombinant strain R15 (SG104, ?pgi, ?pgm, and RBSL5-zwf). Strain R04 (SG104 and ?pgi) reached high-density in a 1-L fermenter when using glucose and glycerol as a mixed carbon source. In scaled-up fed-batch bioconversion in situ using strain R04, 0.82 mol inositol/mol glucose was produced within 23 h, corresponding to a titer of 106.3 g/L (590.5 mM) inositol. CONCLUSIONS:The biosynthesis of inositol from glucose in recombinant E. coli was optimized by metabolic engineering strategies. The metabolically engineered E. coli strains represent a promising method for future inositol production. This study provides an essential reference to obtain a suitable distribution of carbon flux between glycolysis and inositol synthesis.

Project description:BACKGROUND: Riboflavin (vitamin B2), the precursor of the flavin cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is used commercially as an animal feed supplement and food colorant. E. coli is a robust host for various genetic manipulations and has been employed for efficient production of biofuels, polymers, amino acids, and bulk chemicals. Thus, the aim of this study was to understand the metabolic capacity of E. coli for the riboflavin production by modification of central metabolism, riboflavin biosynthesis pathway and optimization of the fermentation conditions. RESULTS: The basic producer RF01S, in which the riboflavin biosynthesis genes ribABDEC from E. coli were overexpressed under the control of the inducible trc promoter, could accumulate 229.1 mg/L of riboflavin. Further engineering was performed by examining the impact of expression of zwf (encodes glucose 6-phosphate dehydrogenase) and gnd (encodes 6-phosphogluconate dehydrogenase) from Corynebacterium glutamicum and pgl (encodes 6-phosphogluconolactonase) from E. coli on riboflavin production. Deleting pgi (encodes glucose-6-phosphate isomerase) and genes of Entner-Doudoroff (ED) pathway successfully redirected the carbon flux into the oxidative pentose phosphate pathway, and overexpressing the acs (encodes acetyl-CoA synthetase) reduced the acetate accumulation. These modifications increased riboflavin production to 585.2 mg/L. By further modulating the expression of ribF (encodes riboflavin kinase) for reducing the conversion of riboflavin to FMN in RF05S, the final engineering strain RF05S-M40 could produce 1036.1 mg/L riboflavin in LB medium at 37°C. After optimizing the fermentation conditions, strain RF05S-M40 produced 2702.8 mg/L riboflavin in the optimized semi-defined medium, which was a value nearly 12-fold higher than that of RF01S, with a yield of 137.5 mg riboflavin/g glucose. CONCLUSIONS: The engineered strain RF05S-M40 has the highest yield among all reported riboflavin production strains in shake flask culture. This work collectively demonstrates that E. coli has a potential to be a microbial cell factory for riboflavin bioproduction.

Project description:BackgroundShikimic acid (SA) produced from the seeds of Chinese star anise (Illicium verum) is a key intermediate for the synthesis of neuraminidase inhibitors such as oseltamivir (Tamiflu®), an anti-influenza drug. However, plants cannot deliver a stable supply of SA. To avoid the resulting shortages and price fluctuations, a stable source of affordable SA is required. Although recent achievements in metabolic engineering of Escherichia coli strains have significantly increased SA productivity, commonly-used plasmid-based expression systems are prone to genetic instability and require constant selective pressure to ensure plasmid maintenance. Cofactors also play an important role in the biosynthesis of different fermentation products. In this study, we first constructed an E. coli SA production strain that carries no plasmid or antibiotic marker. We then investigated the effect of endogenous NADPH availability on SA production.ResultsThe pps and csrB genes were first overexpressed by replacing their native promoter and integrating an additional copy of the genes in a double gene knockout (aroK and aroL) of E. coli. The aroG(fbr), aroB, aroE and tktA gene cluster was integrated into the above E. coli chromosome by direct transformation. The gene copy number was then evolved to the desired value by triclosan induction. The resulting strain, E. coli SA110, produced 8.9-fold more SA than did the parental strain E. coli (?aroK?aroL). Following qRT-PCR analysis, another copy of the tktA gene under the control of the 5P(tac) promoter was inserted into the chromosome of E. coli SA110 to obtain the more productive strain E. coli SA110. Next, the NADPH availability was increased by overexpressing the pntAB or nadK genes, which further enhanced SA production. The final strain, E. coli SA116, produced 3.12 g/L of SA with a yield on glucose substrate of 0.33 mol/mol.ConclusionAn SA-producing E. coli strain that carries neither a plasmid nor an antibiotic marker was constructed by triclosan-induced chromosomal evolution. We present the first demonstration that increasing NADPH availability by overexpressing the pntAB or nadK genes significantly enhances SA production.

Project description:BackgroundL(-)-carnitine production has been widely studied because of its beneficial properties on various diseases and dysfunctions. Enterobacteria possess a specific biotransformation pathway which can be used for the enantioselective production of L(-)-carnitine. Although bioprocesses catalyzed by enzymes or whole cells can overcome the lack of enantioselectivity of chemical methods, current processes for L(-)-carnitine production still have severe disadvantages, such as the low yields, side reactions and the need of high catalyst concentrations and anaerobic conditions for proper expression of the biotransformation pathway. Additionally, genetically engineered strains so far constructed for L(-)-carnitine production are based on plasmids and, therefore, suffer from segregational unstability.ResultsIn this work, a stable, high yielding strain for L(-)-carnitine production from low cost substrates was constructed. A metabolic engineering strategy was implemented in a multiple mutant for use in both growing and resting cells systems. The effect of mutations on gene expression and metabolism was analyzed to characterize the productivity constraints of the wild type and the overproducer strains. Precise deletion of genes which encode proteins of central and carnitine metabolisms were performed. Specifically, flux through the TCA cycle was increased by deletion of aceK (which encodes a bifunctional kinase/phosphatase which inhibits isocitrate dehydrogenase activity) and the synthesis of the by-product ?-butyrobetaine was prevented by deletion of caiA (which encodes a crotonobetainyl-CoA reductase). Both mutations led to improve the L(-)-carnitine production by 20 and 42%, respectively. Moreover, the highly regulated promoter of the cai operon was substituted by a constitutive artificial promoter increasing the biotransformation rate, even under aerobic conditions. Resting cells of the BW ?aceK ?caiA p37cai strain produced 59.6 mmol l(-1)?·?h(-1) of L(-)-carnitine, doubling the productivity of the wild type strain. In addition, almost total conversion was attained in less than two hours without concomitant production of the side product ?-butyrobetaine.ConclusionsL(-)-carnitine production has been enhanced by strain engineering. Metabolic engineering strategies herein implemented allowed obtaining a robust and high yielding E. coli strain. The new overproducer strain attained almost complete conversion of crotonobetaine into L(-)-carnitine with growing and resting cells, and even under aerobic conditions, overcoming the main environmental restriction to carnitine metabolism expression. So far, this is the best performing L(-)-carnitine production E. coli strain described.

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Production of a novel quercetin glycoside through metabolic engineering of Escherichia coli.

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Production of a novel quercetin glycoside through metabolic engineering of Escherichia coli.

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