Vanda Mimi Palmer (VMP), an orchid hybrid of Vanda tesselata and Vanda Tan Chay Yan is a highly scented tropical orchid which blooms all year round. Previous studies revealed that VMP produces a variety of isoprenoid volatiles during daylight. Isoprenoids are well known to contribute significantly to the scent of most fragrant plants. They are a large group of secondary metabolites which may possess valuable characteristics such as flavor, fragrance and toxicity and are produced via two pathways, the mevalonate (MVA) pathway or/and the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. In this study, a sesquiterpene synthase gene denoted VMPSTS, previously isolated from a floral cDNA library of VMP was cloned and expressed in Lactococcus lactis to characterize the functionality of the protein. L. lactis, a food grade bacterium which utilizes the mevalonate pathway for isoprenoid production was found to be a suitable host for the characterization of plant terpene synthases. Through recombinant expression of VMPSTS, it was revealed that VMPSTS produced multiple sesquiterpenes and germacrene D dominates its profile.

Sandalwood oil is one of the worlds most highly prized fragrances. To identify the genes and encoded enzymes responsible for santalene biosynthesis, we cloned and characterized three orthologous terpene synthase (TPS) genes SaSSy, SauSSy, and SspiSSy from three divergent sandalwood species; Santalum album, S. austrocaledonicum, and S. spicatum, respectively. The encoded enzymes catalyze the formation of α-, β-, epi-β-santalene, and α-exo-bergamotene from (E,E)-farnesyl diphosphate (E,E-FPP). Recombinant SaSSy was additionally tested with (Z,Z)-farnesyl diphosphate (Z,Z-FPP) and remarkably, found to produce a mixture of α-endo-bergamotene, α-santalene,(Z)-β-farnesene, epi-β-santalene, and β-santalene. Additional cDNAs that encode bisabolene/bisabolol synthases were also cloned and functionally characterized from these three species. Both the santalene synthases and the bisabolene/bisabolol synthases reside in the TPS-b phylogenetic clade, which is more commonly associated with angiosperm monoterpene synthases. An orthologous set of TPS-a synthases responsible for formation of macrocyclic and bicyclic sesquiterpenes were characterized. Strict functionality and limited sequence divergence in the santalene and bisabolene synthases are in contrast to the TPS-a synthases, suggesting these compounds have played a significant role in the evolution of the Santalum genus.

Taxol (paclitaxel) is a potent anticancer drug first isolated from the Taxus brevifolia Pacific yew tree. Currently, cost-efficient production of Taxol and its analogs remains limited. Here, we report a multivariate-modular approach to metabolic-pathway engineering that succeeded in increasing titers of taxadiene--the first committed Taxol intermediate--approximately 1 gram per liter (~15,000-fold) in an engineered Escherichia coli strain. Our approach partitioned the taxadiene metabolic pathway into two modules: a native upstream methylerythritol-phosphate (MEP) pathway forming isopentenyl pyrophosphate and a heterologous downstream terpenoid-forming pathway. Systematic multivariate search identified conditions that optimally balance the two pathway modules so as to maximize the taxadiene production with minimal accumulation of indole, which is an inhibitory compound found here. We also engineered the next step in Taxol biosynthesis, a P450-mediated 5α-oxidation of taxadiene to taxadien-5α-ol. More broadly, the modular pathway engineering approach helped to unlock the potential of the MEP pathway for the engineered production of terpenoid natural products.

Synthetic biology is the attempt to apply the concepts of engineering to biological systems with the aim to create organisms with new emergent properties. These organisms might have desirable novel biosynthetic capabilities, act as biosensors or help us to understand the intricacies of living systems. This approach has the potential to assist the discovery and production of pharmaceutical compounds at various stages. New sources of bioactive compounds can be created in the form of genetically encoded small molecule libraries. The recombination of individual parts has been employed to design proteins that act as biosensors, which could be used to identify and quantify molecules of interest. New biosynthetic pathways may be designed by stitching together enzymes with desired activities, and genetic code expansion can be used to introduce new functionalities into peptides and proteins to increase their chemical scope and biological stability. This review aims to give an insight into recently developed individual components and modules that might serve as parts in a synthetic biology approach to pharmaceutical biotechnology.

An acyclic diterpene alcohol,(E,E,E)-geranylgeraniol (GGOH), is one of the important compounds used as perfume and pharmacological agents. A deficiency of squalene (SQ) synthase activity allows yeasts to accumulate an acyclic sesquiterpene alcohol,(E,E)-farnesol, in their cells. Since sterols are essential for the growth of yeasts, a deficiency of SQ synthase activity makes the addition of supplemental sterols to the culture media necessary. To develop a GGOH production method not requiring any supplemental sterols, we overexpressed HMG1 encoding hydroxymethylglutaryl-CoA reductase and the genes of two prenyl diphosphate synthases, ERG20 and BTS1, in Saccharomyces cerevisiae. A prototrophic diploid coexpressing HMG1 and the ERG20-BTS1 fusion accumulated GGOH with neither disruption of the SQ synthase gene nor the addition of any supplemental sterols. The GGOH content on the diploid cultivation in a 5-l jar fermenter reached 138.8 mg/l under optimal conditions.

In the urgent search for more effective ways to treat cancer, new extraction methods of taxol from endophytic fungus have demonstrated high potential in increasing the efficiency of taxol extraction for more efficient and sustainable production of taxol and cancer treatment products. This paper summarizes recent advances in taxol-producing endophytic fungi, both in China and abroad, in the following areas: isolation and identification of endophytic fungi types, extraction and detection methods of endophytic taxol in plants, and improved efficiency of the extraction process. With the advancement of science and technology, new techniques in biotechnology, such as fungal strain improvement and recombining technique and microbial fermentation engineering, have increased the extraction yield from taxol-producing fungi, thereby improved the overall efficiency of taxol production.

For a long time people are using plants not only as crop cultures but also for obtaining of various chemicals. Currently plants remain one of the most important and essential sources of biologically active compounds in spite of progress in chemical or microbial synthesis. In our review we compare potentials and perspectives of modern genetic engineering approaches for pharmaceutical biotechnology and give examples of actual biotechnological systems used for production of several promising natural compounds: artemisinin, paclitaxel and scopolamine.

Terpenoids belong to the largest class of natural compounds and are produced in all living organisms. The isoprenoid skeleton is based on assembling of C5 building blocks, but the biosynthesis of a great variety of terpenoids ranging from monoterpenoids to polyterpenoids is not fully understood today. Terpenoids play a fundamental role in human nutrition, cosmetics, and medicine. In the past 10 years, many metabolic engineering efforts have been undertaken in plants but also in microorganisms to improve the production of various terpenoids like artemisinin and paclitaxel. Recently, inverse metabolic engineering and combinatorial biosynthesis as main strategies in synthetic biology have been applied to produce high-cost natural products like artemisinin and paclitaxel in heterologous microorganisms. This review describes the recent progresses made in metabolic engineering of the terpenoid pathway with particular focus on fundamental aspects of host selection, vector design, and system biotechnology.

A eukaryotic mevalonate pathway transferred and expressed in Escherichia coli, and a mammalian hydrocortisone biosynthetic pathway rebuilt in Saccharomyces cerevisiae are examples showing that transferring metabolic pathways from one organism to another can have a powerful impact on cell properties. In this study, we reconstructed the E. coli isoprenoid biosynthetic pathway in S. cerevisiae. Genes encoding the seven enzymatic steps of the pathway were cloned and expressed in S. cerevisiae. mRNA from the seven genes was detected, and the pathway was shown able to sustain growth of yeast in conditions of inhibition of its constitutive isoprenoid biosynthetic pathway.

The biosynthesis of vitamin B(12) is summarized, emphasizing the differences observed between the aerobic and anaerobic pathways. The biosynthetic route to adenosylcobalamin from its five-carbon precursor, 5-aminolaevulinic acid, can be divided into three sections:(1) the biosynthesis of uroporphyrinogen III from 5-aminolaevulinic acid, which is common to both pathways;(2) the conversion of uroporphyrinogen III into the ring-contracted, deacylated intermediate precorrin 6 or cobalt-precorrin 6, which includes the primary differences between the two pathways; and (3) the transformation of this intermediate to form adenosylcobalamin.

BACKGROUND The crystal structure of precorrin-8x methyl mutase (CobH), an enzyme of the aerobic pathway to vitamin B12, provides evidence that the mechanism for methyl migration can plausibly be regarded as an allowed [1,5]-sigmatropic shift of a methyl group from C-11 to C-12 at the C ring of precorrin-8x to afford hydrogenobyrinic acid. RESULTS The dimeric structure of CobH creates a set of shared active sites that readily discriminate between different tautomers of precorrin-8x and select a discrete tautomer for sigmatropic rearrangement. The active site contains a strictly conserved histidine residue close to the site of methyl migration in ring C of the substrate. CONCLUSION Analysis of the structure with bound product suggests that the [1,5]-sigmatropic shift proceeds by protonation of the ring C nitrogen, leading to subsequent methyl migration.

The manner in which vitamin B12 is synthesized is detailed with emphasis on the different mechanisms for ring contraction encountered in aerobic and anaerobic organisms. The aerobic process utilizes two enzymes and is dependent on molecular oxygen, in stark contrast to the anaerobic mechanism which is controlled by cobalt and requires only one enzyme.

The construction of a new recombinant strain of Escherichia coli in which two vitamin B12 biosynthetic genes, cobA and cobI, from Pseudomonas denitrificans are simultaneously overexpressed has resulted in the in vivo synthesis and accumulation of Factor III, an isobacteriochlorin not normally synthesized in E. coli. A lysate of the new strain can take the place of two lysates normally required to provide uroporphyrinogen III methyltransferase (cobA) and precorrin-2 methyltransferase (cobI) in an anaerobic five-enzyme synthesis of the early B12 intermediate, precorrin-3 (the reduced form of Factor III) from delta-aminolevulinic acid.

Taxadiene synthase catalyzes the conversion of the universal precursor of diterpenoids, geranylgeranyl diphosphate, to taxadiene, a key intermediate in Taxol (paclitaxel) biosynthesis. The gene encoding taxadiene synthase was cloned recently. Here we report a method for the heterologous overexpression of cDNA encoding taxadiene synthase in Escherichia coli using a thioredoxin fusion expression system, which increases the solubility of expressed protein. Taxadiene synthase cDNA was amplified by polymerase chain reaction and then subcloned into pET3d and pET32a(+) to form pET3dTX and pET32TX, respectively. The expressed taxadiene synthase from E. coli BL21(DE3)/pET3dTX was present completely as inclusion bodies. The transformant E. coli BL21(DE3)/pET32TX produced a thioredoxin fusion taxadiene synthase (15-20% of total soluble protein) when induced with isopropyl beta-D-thiogalactopyranoside at low temperature (20 degrees C). The recombinant enzyme was purified by a single step with a His-binding metal affinity column. The maximal production attained was 13 mg of purified, active fusion protein per 500 ml culture of E. coli BL21(DE3)/pET32TX. The purified recombinant taxadiene synthase fusion protein was similar to native protein in steady-state kinetic parameters and mobility on sodium sulfate-polyacrylamide gel electrophoresis. The protein purified from E. coli BL21(DE3)/pET3dTX had the expected N-terminal (AQLSFNA) sequence.

BACKGROUND: Genetically engineered synthesis, in which the gene products, cofactors, and substrates of a complete pathway are combined in vitro in a single flask to give the target, can be a viable alternative to conventional chemical construction of molecules of complex structure and stereochemistry. We chose to attempt to synthesize the metal-free corrinoid hydrogenobyrinic acid, an advanced precursor of vitamin B12. RESULTS: Cloning and overexpression of the genes necessary for the S-adenosyl methionine dependent conversion of 5-aminolevulinic acid (ALA) to precorrin-3 and those required for the synthesis of hydrogenobyrinic acid from precorrin-3 completed the repertoire of the 12 biosynthetic enzymes involved in corrin synthesis. Using these enzymes and the necessary cofactors, the multi-enzyme synthesis of hydrogenobyrinic acid from ALA can be achieved in 20% overall yield in a single reaction vessel, corresponding to an average of at least 90% conversion for each of the 17 steps involved. CONCLUSIONS: By replacing the cell wall with glass, and by mixing the soluble biosynthetic enzymes and necessary cofactors, the major segment of the physiological synthesis of vitamin B12 has been accomplished. Since only those enzymes necessary for the synthesis of hydrogenobyrinic acid from ALA are supplied, none of the intermediates is deflected from the direct pathway. This results in an efficiency which in fact surpasses that of nature.

BACKGROUND During the biosynthesis of vitamin B12, the aerobic bacterium Pseudomonas denitrificans uses two enzymes, CobG and CobJ, to convert precorrin-3 to the ring-contracted intermediate, precorrin-4. CobG is a monooxygenase that adds a hydroxyl group, derived from molecular oxygen, to C-20, whereas CobJ is bifunctional, inserting a methyl group at C-17 of the macrocycle and catalyzing ring contraction. Molecular oxygen is not available to vitamin B12-producing anaerobic bacteria and members of the ancient Archaea, so the question arises of how these microbes accomplish the key ring-contraction process. RESULTS Cloning and overexpression of Salmonella typhimurium genes has led to the discovery that a single enzyme, CbiH, is responsible for ring contraction during anaerobic biosynthesis of vitamin B12. The process occurs when CbiH is incubated with precorrin-3, but only in the presence of cobalt. CbiH functions as a C-17 methyltransferase and mediates ring contraction and lactonization to yield the intermediate, cobalt-precorrin-4, isolated as cobalt-factor IV. 13C labeling studies have proved that cobalt-precorrin-4 is incorporated into cobyrinic acid, thereby confirming that cobalt-precorrin-4 is an intermediate in vitamin B12 biosynthesis. CONCLUSIONS Two distinct mechanisms exist in nature for the ring contraction of porphyrinoids to corrinoids-an ancient anaerobic pathway that requires cobalt complexation prior to nonoxidative rearrangement, and a more recent aerobic route in which molecular oxygen serves as the cofactor. The present results offer a rationale for the main differences between aerobic and anaerobic biosynthesis of vitamin B12. Thus, in anaerobes there is exchange of oxygen at the C-27 acetate site, extrusion of acetaldehyde and early insertion of cobalt, whereas the aerobes show no exchange of oxygen at C-27, extrude acetic acid and insert cobalt very late in the biosynthetic pathway, after ring contraction has occurred. These parallel routes to vitamin B12 have now been clearly distinguished by their differing mechanisms for ring contraction.

The problems inherent in the enzymatic and chemical synthesis of S-adenosyl-L-methionine (SAM) led us to develop an efficient, simple method for the synthesis of large amounts of labeled SAM. Previously, we reported that the problem of product inhibition of E. coli SAM synthetase encoded by the metK gene was successfully overcome in the presence of sodium p-toluenesulfonate (pTsONa). This research has now been expanded to demonstrate that product inhibition of this enzyme can also be overcome by adding a high concentration of beta-mercaptoethanol (beta ME), acetonitrile, or urea. In addition a recombinant strain of E. coli has been constructed that expresses the yeast SAM synthetase encoded by the sam2 gene. The yeast enzyme does not have the problem of product inhibition seen with the E. coli enzyme. Complete conversion of 10 mM methionine to SAM was achieved in incubations with either the recombinant yeast enzyme and 1 molar potassium ion or the E. coli enzyme in the presence of additives such as beta ME, acetonitrile, urea, or pTsONa. The recombinant yeast SAM synthetase was used to generate SAM in situ for use in the multi-enzymatic synthesis of precorrin 2.

Because many natural products are of biological and medicinal importance, methods are continually being sought for studying their biosynthetic pathways, which may eventually result in increased production and the generation of novel compounds. Advances in genetic engineering have enabled the homologous or heterologous expression of many natural product biosynthetic genes from divergent sources, resulting in a supply of enzymes not readily available by isolation from the producing organism. Mixing and matching of these enzymes in cell-free reactions can provide information, not available by any other means, about enzyme mechanisms, pathway intermediates, and possible variations in the structure of the final product.

Recent studies on ex vivo synthesis of natural products reveal that even complex multistep pathways can be successfully reconstructed. Genetic engineering of such reconstituted pathways has already been used to generate 'unnatural' natural products related to the original compound. In the future, it may be possible to use these approaches to make natural products that are currently inaccessible to conventional synthesis.

We constructed a biosynthetic pathway of isoprene production in Escherichia coli by introducing isoprene synthase (ispS) from Populus alba. 1-deoxy-D-xylulose 5-phosphate synthase (dxs), 1-deoxy-D-xylulose 5-phosphate reductoisomerase (dxr) and isopentenyl diphosphate (IPP) isomerase (idi) were overexpressed to enhance the isoprene production. The isoprene production was improved 0.65, 0.16, and 1.22 fold over the recombinant BL21 (pET-30a-ispS), respectively, and idi was found to be a key regulating point for isoprene production. In order to optimize the production of isoprene in E. coli, we attempted to construct polycistronic operons based on pET-30a with genes dxs, dxr, and idi in various orders. The highest isoprene production yield of 2.727 mg g(-1) h(-1)(per dry weight) was achieved by E. coli transformed with pET-30a-dxs/dxr/idi. Interestingly, the gene order was found to be consistent with that of the metabolic pathway. This indicates that order of genes is a significant concern in metabolic engineering and a sequential expression pattern can be optimized according to the biosynthetic pathway for efficient product synthesis.

Nasutitermes takasagoensis soldiers defend their colonies using characteristic diterpenes. Diterpenes are thought to be synthesized in the frontal gland cells surrounding the gland reservoir. To identify the genes involved in diterpene synthesis, a cDNA library was prepared from the frontal gland cells and exhaustively sequenced using a 454 pyrosequencer (GS Junior; Roche, Branford, CT, USA). A total of 50 290 clean sequences were assembled into 1111 contigs, which were grouped into 774 genes (isogroups). Based on sequence similarity with known proteins, we identified seven genes encoding the following four enzymes associated with diterpene synthesis: 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase (HMGS), HMG-CoA reductase (HMGR), farnesyl diphosphate synthase, and geranylgeranyl diphosphate synthases. The expression levels of two enzymes, HMGS and HMGR, involved in the mevalonate pathway were examined, assuming that the site of the defensive terpenoid synthesis strongly activates the mevalonate pathway, which produces a precursor of terpenoids. Real-time quantitative reverse-transcriptase PCR confirmed significantly higher expression of HMGS and HMGR in the heads of soldiers. We then divided the head into three parts and found that the expression levels of HMGS and HMGR were significantly higher in the part containing class 1 secretory cells of the frontal gland. Overall, the results suggested that the mevalonate pathway for diterpene synthesis occurs in class 1 cells around the frontal gland reservoir.

The vitamin E family consists of 4 tocopherol and 4 tocotrienol compounds. During recent years, tocotrienols have gained increased interest due to their biological activities that are beyond the vitamin E activity. Here we report the engineering of plasmid-free Escherichia coli strains for an efficient synthesis of 2-methyl-6-geranylgeranyl-benzoquinol (MGGBQ), the central precursor for all four natural tocotrienol compounds. Heterologous genes needed for the in vivo synthesis of MGGBQ in E. coli (crtE, hpd, and hpt) were individually integrated into the chromosome of E. coli. The yield of MGGBQ after cultivation of the plasmid-free recombinant E. coli strain was significantly higher (604μg/gcdw) compared to an E. coli strain that carries these biosynthesis genes on a multi-copy expression plasmid (325μg/gcdw). Further chromosomal integration of an additional copy of the isopentenyl-diphosphate isomerase gene (idi) and a subsequent increase in expression level of the deoxy-xylulose synthase gene (dxs) increased the MGGBQ yield by 80%(1110μg/gcdw) and 135%(1425μg/gcdw), respectively. MGGBQ which accumulated in the membrane fraction of the recombinant E. coli cells was isolated and its structure was completely elucidated by 1D and 2D NMR and MS measurements. The engineered, plasmid-free E. coli strain is a promising host for the heterologous in vivo production of tocotrienol and its derivatives.

ABSTRACT: BACKGROUND: 2'-Fucosyllactose (2-FL) is a functional oligosaccharide present in human milk which protects against the infection of enteric pathogens. Because 2-FL can be synthesized through the enzymatic fucosylation of lactose with guanosine 5'-diphosphate (GDP)-L-fucose by alpha-1,2 fucosyltransferase (FucT2), an 2-FL producing Escherichia coli can be constructed through overexpressing genes coding for endogenous GDP-L-fucose biosynthetic enzymes and heterologous fucosyltransferase. RESULTS: The gene for FucT2 from Helicobacter pylori was introduced to the GDP-L-fucose producing recombinant E. coli BL21 star(DE3) strain. However, only small amount of 2-FL was produced in a batch fermentation because the E. coli BL21star(DE3) strain assimilated lactose instead of converting to 2-FL. As an alternative host, the E. coli JM109(DE3) strain which is incapable of assimilating lactose was chosen as a 2-FL producer. Whole cell biosynthesis of 2-FL from lactose was investigated in a series of batch fermentations using various concentrations of lactose. The results of batch fermentations showed that lactose was slowly assimilated by the engineered E. coli JM109(DE3) strain and 2-FL was synthesized without supplementation of another auxiliary sugar for cell growth. A maximum 2-FL concentration of 1.23 g/l was obtained from a batch fermentation with 14.5 g/l lactose. The experimentally obtained yield (g 2-FL/g lactose) corresponded to 20% of the theoretical maximum yield estimated by the elementary flux mode (EFM) analysis. CONCLUSIONS: The experimental 2-FL yield in this study corresponded to about 20% of the theoretical maximum yield, which suggests further modifications via metabolic engineering of a host strain or optimization of fermentation processes might be carried out for improving 2-FL yield. Improvement of microbial production of 2-FL from lactose by engineered E. coli would increase the feasibility of utilizing 2-FL as a prebiotic in various foods.

Escherichia coli offers unparalleled engineering capacity in the context of heterologous natural product biosynthesis. However, as with other heterologous hosts, cellular metabolism must be designed or redesigned to support final compound formation. This task is at once complicated and aided by the fact that the cell does not natively produce an abundance of natural products. As a result, the metabolic engineer avoids complicated interactions with native pathways closely associated with the outcome of interest, but this convenience is tempered by the need to implement the required metabolism to allow functional biosynthesis. This review focuses on engineering E. coli for the purpose of polyisoprene formation, as it is related to isoprenoid compounds currently being pursued through a heterologous approach. In particular, the review features the compound paclitaxel and early efforts to design and overproduce intermediates through E. coli.

The traditional Chinese medicinal plant, Isodon L., is remarkably rich in pharmacologically active ent-kaurane diterpenoids of diverse carbon skeletons. In an effort to create a resource for gene discovery and elucidate the biosynthesis of Isodonent-kaurane diterpenoids, three cDNAs (named IeCPS1, IeCPS2 and IeCPS2a) were isolated putatively encoding copalyl diphosphate synthases from Isodoneriocalyx leaves. Recombinant proteins of IeCPS1 and IeCPS2 were expressed, respectively, in Escherichia coli, and were shown to specifically convert geranylgeranyl diphosphate to copalyl diphosphate as demonstrated by GC-MS analyses. Based on tissue-specific expression and metabolic localization studies, the IeCPS2 transcripts were detected in young and mature leaves where the dominant ent-kaurane diterpenoid maoecrystal B accumulates, whereas no detectable expression of IeCPS2 was observed in germinating seeds where the gibberellin biosynthetic pathway is usually active. In addition, no evidence for maoecrystal B was found in germinating seeds. On the other hand, IeCPS1 transcripts significantly accumulated in germinating seeds as well as in leaves. The biochemical and molecular genetic evidence thus indicated that IeCPS2 is a copalyl diphosphate synthase potentially involved in the biosynthesis of Isodon diterpenoids in leaves, while IeCPS1 is more probably relevant to gibberellin formation and may, in addition, participate in Isodonent-kaurane diterpenoid production.

In this study, PHA biosynthesis operon of Comamonas sp. EB172, an acid-tolerant strain, consisting of three genes encoding acetyl-CoA acetyltransferase (phaA(Co) gene, 1182bp), acetoacetyl-CoA reductase (phaB(Co) gene, 738bp) and PHA synthase, class I (phaC(Co) gene, 1694bp) were identified. Sequence analysis of the phaA(Co), phaB(Co) and phaC(Co) genes revealed that they shared more than 85%, 89% and 69% identity, respectively, with orthologues from Delftia acidovorans SPH-1 and Acidovorax ebreus TPSY. The PHA biosynthesis genes (phaC(Co) and phaAB(Co)) were successfully cloned in a heterologous host, Escherichia coli JM109. E. coli JM109 transformants harbouring pGEM'-phaC(Co)AB(Re) and pGEM'-phaC(Re)AB(Co) were shown to be functionally active synthesising 33wt.% and 17wt.% of poly(3-hydroxybutyrate)[P(3HB)]. E. coli JM109 transformant harbouring the three genes from the acid-tolerant Comamonas sp. EB172 (phaCAB(Co)) under the control of native promoter from Cupriavidus necator, in vivo polymerised P(3HB) when fed with glucose and volatile mixed organic acids (acetic acid:propionic acid:n-butyric acid) in ration of 3:1:1, respectively. The E. coli JM109 transformant harbouring phaCAB(Co) could accumulate P(3HB) at 2g/L of propionic acid. P(3HB) contents of 40.9% and 43.6% were achieved by using 1% of glucose and mixed organic acids, respectively.

The pduP gene encodes a propionaldehyde dehydrogenase (PduP) was investigated for the role in 3-hydroxypropionic acid (3-HP) glycerol metabolism in Klebsiella pneumoniae. The enzyme assay showed that cell extracts from a pduP mutant strain lacked measurable dehydrogenase activity. Additionally, the mutant strain accumulated the cytotoxic intermediate metabolite 3-hydroxypropionaldehyde (3-HPA), causing both cell death and a lower final 3-HP titer. Ectopic expression of pduP restored normal cell growth to mutant. The enzymatic property of recombinant protein from Escherichia coli was examined, exhibiting a broad substrate specificity, being active on 3-HPA. The present work is thus the first to demonstrate the role of PduP in glycerol metabolism and biosynthesis of 3-HP.

In this work, Escherichia coli was engineered to produce a medically valuable cofactor, coenzyme Q(10)(CoQ(10)), by removing the endogenous octaprenyl diphosphate synthase gene and functionally replacing it with a decaprenyl diphosphate synthase gene from Sphingomonas baekryungensis. In addition, by over-expressing genes coding for rate-limiting enzymes of the aromatic pathway, biosynthesis of the CoQ(10) precursor para-hydroxybenzoate (PHB) was increased. The production of isoprenoid precursors of CoQ(10) was also improved by the heterologous expression of a synthetic mevalonate operon, which permits the conversion of exogenously supplied mevalonate to farnesyl diphosphate. The over-expression of these precursors in the CoQ(10)-producing E. coli strain resulted in an increase in CoQ(10) content, as well as in the accumulation of an intermediate of the ubiquinone pathway, decaprenylphenol (10P-Ph). In addition, the over-expression of a PHB decaprenyl transferase (UbiA) encoded by a gene from Erythrobacter sp. NAP1 was introduced to direct the flux of DPP and PHB towards the ubiquinone pathway. This further increased CoQ(10) content in engineered E. coli, but decreased the accumulation of 10P-Ph. Finally, we report that the combined over-production of isoprenoid precursors and over-expression of UbiA results in the decaprenylation of para-aminobenzoate, a biosynthetic precursor of folate, which is structurally similar to PHB.

Taxa-4(5),11(12)-diene is the first dedicated intermediate in the metabolic pathway responsible for synthesizing the anticancer compound Taxol. In this study, the heterologous production of taxadiene was established in and analyzed between K- and B-derived Escherichia coli strains. First, recombinant parameters associated with precursor metabolism (the upstream methylerythritol phosphate (MEP) pathway) and taxadiene biosynthesis (the downstream pathway) were varied to probe the effect different promoters and cellular backgrounds have on taxadiene production. Specifically, upstream MEP pathway genes responsible for the taxadiene precursors, dimethylallyl diphosphate and isopentenyl diphosphate, were tested with an inducible T7 promoter system within K and B E. coli strains. Whereas, inducible T7, Trc, and T5 promoters were tested with the plasmid-borne geranylgeranyl diphosphate synthase and taxadiene synthase genes responsible for the downstream pathway. The K-derivative produced taxadiene roughly 2.5-fold higher than the B-derivative. A transcriptomics study revealed significant differences in pyruvate metabolism between the K and B strains, providing insight into the differences observed in taxadiene biosynthesis and targets for future metabolic engineering efforts. Next, the effect of temperature on cell growth and taxadiene production was analyzed in these two strains, revealing similar phenotypes between the two with 22°C as the optimal production temperature. Lastly, the effect of indole on cell growth was investigated between the two strains, showing that the K-derivative demonstrated greater growth inhibition compared to the B-derivative.