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1.
  • Almquist, Joachim, 1980, et al. (författare)
  • Kinetic models in industrial biotechnology - Improving cell factory performance
  • 2014
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 24, s. 38-60
  • Tidskriftsartikel (refereegranskat)abstract
    • An increasing number of industrial bioprocesses capitalize on living cells by using them as cell factories that convert sugars into chemicals. These processes range from the production of bulk chemicals in yeasts and bacteria to the synthesis of therapeutic proteins in mammalian cell lines. One of the tools in the continuous search for improved performance of such production systems is the development and application of mathematical models. To be of value for industrial biotechnology, mathematical models should be able to assist in the rational design of cell factory properties or in the production processes in which they are utilized. Kinetic models are particularly suitable towards this end because they are capable of representing the complex biochemistry of cells in a more complete way compared to most other types of models. They can, at least in principle, be used to in detail understand, predict, and evaluate the effects of adding, removing, or modifying molecular components of a cell factory and for supporting the design of the bioreactor or fermentation process. However, several challenges still remain before kinetic modeling will reach the degree of maturity required for routine application in industry. Here we review the current status of kinetic cell factory modeling. Emphasis is on modeling methodology concepts, including model network structure, kinetic rate expressions, parameter estimation, optimization methods, identifiability analysis, model reduction, and model validation, but several applications of kinetic models for the improvement of cell factories are also discussed.
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2.
  • Asadollahi, M. A., et al. (författare)
  • Enhancing sesquiterpene production in Saccharomyces cerevisiae through in silico driven metabolic engineering
  • 2009
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 11:6, s. 328-334
  • Tidskriftsartikel (refereegranskat)abstract
    • A genome-scale metabolic model was used to identify new target genes for enhanced biosynthesis of sesquiterpenes in the yeast Saccharomyces cerevisiae. The effect of gene deletions on the flux distributions in the metabolic model of S. cerevisiae was assessed using Opt Gene as the modeling framework and minimization of metabolic adjustments (MOMA) as objective function. Deletion of NADPH-dependent glutamate dehydrogenase encoded by GDH1 was identified as the best target gene for the improvement of sesquiterpene biosynthesis in yeast. Deletion of this gene enhances the available NADPH in the cytosol for other NADPH requiring enzymes, including HMG-CoA reductase. However, since disruption of GDH1 impairs the ammonia utilization, simultaneous over-expression of the NADH-dependent glutamate dehydrogenase en coded by GDH2 was also considered in this study. Deletion of GDH1 led to an approximately 85% increase in the final cubebol titer. However, deletion of this gene also caused a significant decrease in the maximum specific growth rate. Over-expression of GDH2 did not show a further effect on the final cubebol titer but this alteration significantly improved the growth rate compared to the GDH1 deleted strain. (C) 2009 Elsevier Inc. All rights reserved.
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3.
  • Aslan, Selcuk, et al. (författare)
  • Wax esters of different compositions produced via engineering of leaf chloroplast metabolism in Nicotiana benthamiana
  • 2014
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 25, s. 103-112
  • Tidskriftsartikel (refereegranskat)abstract
    • In a future bin based economy, renewable sources for lipid compounds at attractive cost are needed for applications where today petrochemical derivatives are dominating. Wax esters and fatty alcohols provide diverse industrial uses, such as in lubricant and surfactant production. In this study, chloroplast metabolism was engineered to divert intermediates from de nova fatty acid biosynthesis to wax ester synthesis. To accomplish this, chloroplast targeted fatty acyl recluctases (EAR) and wax ester synthases (WS) were transiently expressed in Nic"onana benthamiuna loaves. Wax esters of different qualities and quantities were produced providing insights to the properties and interaction of the individual enzymes used. In particular, a phytyl ester synthase was found to be a premium candidate for medium chain wax ester synthesis. Catalytic activities of FAR and WS were also expressed as a fusion protein and determined functionally equivalent to the expression of individual enzymes for wax ester synthesis in chloroplasts. (C) 2014 The Authors. Published by Elsevier Inc. On behalf of International Metabolic Engineering Society.
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4.
  • Asplund-Samuelsson, Johannes, et al. (författare)
  • Thermodynamic analysis of computed pathways integrated into the metabolic networks of E. coli and Synechocystis reveals contrasting expansion potential
  • 2018
  • Ingår i: Metabolic engineering. - : Academic Press Inc.. - 1096-7176 .- 1096-7184. ; 45, s. 223-236
  • Tidskriftsartikel (refereegranskat)abstract
    • Introducing biosynthetic pathways into an organism is both reliant on and challenged by endogenous biochemistry. Here we compared the expansion potential of the metabolic network in the photoautotroph Synechocystis with that of the heterotroph E. coli using the novel workflow POPPY (Prospecting Optimal Pathways with PYthon). First, E. coli and Synechocystis metabolomic and fluxomic data were combined with metabolic models to identify thermodynamic constraints on metabolite concentrations (NET analysis). Then, thousands of automatically constructed pathways were placed within each network and subjected to a network-embedded variant of the max-min driving force analysis (NEM). We found that the networks had different capabilities for imparting thermodynamic driving forces toward certain compounds. Key metabolites were constrained differently in Synechocystis due to opposing flux directions in glycolysis and carbon fixation, the forked tri-carboxylic acid cycle, and photorespiration. Furthermore, the lysine biosynthesis pathway in Synechocystis was identified as thermodynamically constrained, impacting both endogenous and heterologous reactions through low 2-oxoglutarate levels. Our study also identified important yet poorly covered areas in existing metabolomics data and provides a reference for future thermodynamics-based engineering in Synechocystis and beyond. The POPPY methodology represents a step in making optimal pathway-host matches, which is likely to become important as the practical range of host organisms is diversified. 
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5.
  • Baebprasert, Wipawee, et al. (författare)
  • Increased H(2) production in the cyanobacterium Synechocystis sp strain PCC 6803 by redirecting the electron supply via genetic engineering of the nitrate assimilation pathway
  • 2011
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 13:5, s. 610-616
  • Tidskriftsartikel (refereegranskat)abstract
    • The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 contains a single bidirectional NiFe-Hox-hydrogenase, which evolves hydrogen under certain environmental conditions. The nitrate assimilation pathway is a potential competing pathway that may reduce the electron flow to the hydrogenase and thereby limit hydrogen production. To improve H(2) production, the nitrate assimilation pathway was disrupted by genetic engineering to redirect the electron flow towards the Hox-hydrogenase. Mutant strains disrupted in either nitrate reductase (Delta narB) or nitrite reductase (Delta nirA) or both nitrate reductase and nitrite reductase (Delta narB:Delta nirA) were constructed and tested for their ability to produce hydrogen. H(2) production and Hox-hydrogenase activities in all the mutant strains were higher than those in wild-type. Highest H(2) production was observed in the Delta narB:Delta nirA strain. Small changes were observed for Hox-hydrogenase enzyme activities and only minor changes in transcript levels of hoxH and hoxY were not correlated with H(2) production. The results suggest that the high rate of H(2) production observed in the Delta narB:Delta nirA strain of the cyanobacterium Synechocystis sp. strain PCC 6803 is the result of redirecting the electron supply from the nitrate assimilation pathway, through genetic engineering, towards the Hox-hydrogenase.
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6.
  • Borodina, I., et al. (författare)
  • Establishing a synthetic pathway for high-level production of 3-hydroxypropionic acid in Saccharomyces cerevisiae via beta-alanine
  • 2015
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 27, s. 57-64
  • Tidskriftsartikel (refereegranskat)abstract
    • Microbial fermentation of renewable feedstocks into plastic monomers can decrease our fossil dependence and reduce global CO2 emissions. 3-Hydroxypropionic acid (3HP) is a potential chemical building block for sustainable production of superabsorbent polymers and acrylic plastics. With the objective of developing Saccharolnyces cerevisiae as an efficient cell factory for high-level production of 3HP, we identified the beta-alanine biosynthetic route as the most economically attractive according to the metabolic modeling. We engineered and optimized a synthetic pathway for de novo biosynthesis of beta-alanine and its subsequent conversion into 3HP using a novel beta-alanine-pyruvate aminotransferase discovered in Bacillus cereus. The final strain produced 3HP at a titer of 13.7 +/- 0.3 g L-1 with a 0.14 +/- 0.0 C-mol C-mol(-1) yield on glucose in 80 h in controlled fed-batch fermentation in mineral medium at pH 5, and this work therefore lays the basis for developing a process for biological 3HP production.
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7.
  • Cao, Xuan, et al. (författare)
  • Engineering yeast for high-level production of diterpenoid sclareol
  • 2023
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 75, s. 19-28
  • Tidskriftsartikel (refereegranskat)abstract
    • The diterpenoid sclareol is an industrially important precursor for alternative sustainable supply of ambergris. However, its current production from plant extraction is neither economical nor environmental-friendly, since it requires laborious and cost-intensive purification procedures and plants cultivation is susceptible to environmental factors. Engineering cell factories for bio-manufacturing can enable sustainable production of natural products. However, stringent metabolic regulation poses challenges to rewire cellular metabolism for overproduction of compounds of interest. Here we used a modular approach to globally rewire the cellular metabolism for improving sclareol production to 11.4 g/L in budding yeast Saccharomyces cerevisiae, the highest reported diterpenoid titer in microbes. Metabolic flux analysis showed that modular balanced metabolism drove the metabolic flux toward the biosynthesis of targeted molecules, and transcriptomic analysis revealed that the expression of central metabolism genes was shaped for a new balanced metabolism, which laid a foundation in extensive metabolic engineering of other microbial species for sustainable bio-production.
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8.
  • Chen, Que, et al. (författare)
  • Combining retinal-based and chlorophyll-based (oxygenic) photosynthesis : Proteorhodopsin expression increases growth rate and fitness of a Delta PSI strain of Synechocystis sp. PCC6803
  • 2019
  • Ingår i: Metabolic engineering. - : Elsevier. - 1096-7176 .- 1096-7184. ; 52, s. 68-76
  • Tidskriftsartikel (refereegranskat)abstract
    • To fill the "green absorption gap", a green absorbing proteorhodopsin was expressed in a PSI-deletion strain (Delta PSI) of Synechocystis sp. PCC6803. Growth-rate measurements, competition experiments and physiological characterization of the proteorhodopsin-expressing strains, relative to the Delta PSI control strain, allow us to conclude that proteorhodopsin can enhance the rate of photoheterotrophic growth of Delta PSI Synechocystis strain. The physiological characterization included measurement of the amount of residual glucose in the spent medium and analysis of oxygen uptake- and production rates. To explore the use of solar radiation beyond the PAR region, a red-shifted variant Proteorhodopsin-D212N/F234S was expressed in a retinal-deficient PSI-deletion strain (Delta PSI/Delta SynACO). Via exogenous addition of retinal analogue an infrared absorbing pigment (maximally at 740 nm) was reconstituted in vivo. However, upon illumination with 746 nm light, it did not significantly stimulate the growth (rate) of this mutant. The inability of the proteorhodopsin-expressing Delta PSI strain to grow photoautotrophically is most likely due to a kinetic rather than a thermodynamic limitation of its NADPH-dehydrogenase in NADP(+)-reduction.
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9.
  • Chen, Xin, 1980, et al. (författare)
  • Suppressors of amyloid-β toxicity improve recombinant protein production in yeast by reducing oxidative stress and tuning cellular metabolism
  • 2022
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 72, s. 311-324
  • Tidskriftsartikel (refereegranskat)abstract
    • High-level production of recombinant proteins in industrial microorganisms is often limited by the formation of misfolded proteins or protein aggregates, which consequently induce cellular stress responses. We hypothesized that in a yeast Alzheimer's disease (AD) model overexpression of amyloid-β peptides (Aβ42), one of the main peptides relevant for AD pathologies, induces similar phenotypes of cellular stress. Using this humanized AD model, we previously identified suppressors of Aβ42 cytotoxicity. Here we hypothesize that these suppressors could be used as metabolic engineering targets to alleviate cellular stress and improve recombinant protein production in the yeast Saccharomyces cerevisiae. Forty-six candidate genes were individually deleted and twenty were individually overexpressed. The positive targets that increased recombinant α-amylase production were further combined leading to an 18.7-fold increased recombinant protein production. These target genes are involved in multiple cellular networks including RNA processing, transcription, ER-mitochondrial complex, and protein unfolding. By using transcriptomics and proteomics analyses, combined with reverse metabolic engineering, we showed that reduced oxidative stress, increased membrane lipid biosynthesis and repressed arginine and sulfur amino acid biosynthesis are significant pathways for increased recombinant protein production. Our findings provide new insights towards developing synthetic yeast cell factories for biosynthesis of valuable proteins.
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10.
  • Chen, Yun, 1978, et al. (författare)
  • Coupled incremental precursor and co-factor supply improves 3-hydroxypropionic acid production in Saccharomyces cerevisiae
  • 2014
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 22, s. 104-109
  • Tidskriftsartikel (refereegranskat)abstract
    • 3-Hydroxypropionic acid (3-HP) is an attractive platform chemical, which can be used to produce a variety of commodity chemicals, such as acrylic acid and acrylamide. For enabling a sustainable alternative to petrochemicals as the feedstock for these commercially important chemicals, fermentative production of 3-HP is widely investigated and is centered on bacterial systems in most cases. However, bacteria present certain drawbacks for large-scale organic acid production. In this study, we have evaluated the production of 3-HP in the budding yeast Saccharomyces cerevisiae through a route from malonyl-CoA, because this allows performing the fermentation at low pH thus making the overall process cheaper. We have further engineered the host strain by increasing availability of the precursor malonyl-CoA and by coupling the production with increased NADPH supply we were able to substantially improve 3-HP production by five-fold, up to a final titer of 463 mg l(-1). Our work thus led to a demonstration of 3-HP production in yeast via the malonyl-CoA pathway, and this opens for the use of yeast as a cell factory for production of bio-based 3-HP and derived acrylates in the future. (C) 2014 International Metabolic Engineering Society.
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11.
  • Chen, Yun, 1978, et al. (författare)
  • Establishing a platform cell factory through engineering of yeast acetyl-CoA metabolism
  • 2013
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 15:1, s. 48-54
  • Tidskriftsartikel (refereegranskat)abstract
    • Production of fuels and chemicals by industrial biotechnology requires efficient, safe and flexible cell factory platforms that can be used for production of a wide range of compounds. Here we developed a platform yeast cell factory for efficient provision of acetyl-CoA that serves as precursor metabolite for a wide range of industrially interesting products. We demonstrate that the platform cell factory can be used to improve the production of alpha-santalene, a plant sesquiterpene that can be used as a perfume by four-fold. This strain would be a useful tool to produce a wide range of acetyl-CoA-derived products.
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12.
  • Choi, BoHyun, 1986, et al. (författare)
  • Engineering of Saccharomyces cerevisiae for enhanced metabolic robustness and L-lactic acid production from lignocellulosic biomass
  • 2024
  • Ingår i: Metabolic Engineering. - 1096-7176 .- 1096-7184. ; 84, s. 23-33
  • Tidskriftsartikel (refereegranskat)abstract
    • Metabolic engineering for high productivity and increased robustness is needed to enable sustainable biomanufacturing of lactic acid from lignocellulosic biomass. Lactic acid is an important commodity chemical used for instance as a monomer for production of polylactic acid, a biodegradable polymer. Here, rational and model-based optimization was used to engineer a diploid, xylose fermenting Saccharomyces cerevisiae strain to produce L-lactic acid. The metabolic flux was steered towards lactic acid through the introduction of multiple lactate dehydrogenase encoding genes while deleting ERF2, GPD1, and CYB2. A production of 93 g/L of lactic acid with a yield of 0.84 g/g was achieved using xylose as the carbon source. To increase xylose utilization and reduce acetic acid synthesis, PHO13 and ALD6 were also deleted from the strain. Finally, CDC19 encoding a pyruvate kinase was overexpressed, resulting in a yield of 0.75 g lactic acid/g sugars consumed, when the substrate used was a synthetic lignocellulosic hydrolysate medium, containing hexoses, pentoses and inhibitors such as acetate and furfural. Notably, modeling also provided leads for understanding the influence of oxygen in lactic acid production. High lactic acid production from xylose, at oxygen-limitation could be explained by a reduced flux through the oxidative phosphorylation pathway. On the contrast, higher oxygen levels were beneficial for lactic acid production with the synthetic hydrolysate medium, likely as higher ATP concentrations are needed for tolerating the inhibitors therein. The work highlights the potential of S. cerevisiae for industrial production of lactic acid from lignocellulosic biomass.
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13.
  • Demski, Kamil, et al. (författare)
  • Manufacturing specialized wax esters in plants
  • 2022
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 72, s. 391-402
  • Tidskriftsartikel (refereegranskat)abstract
    • Biologically produced wax esters can fulfil different industrial purposes. These functionalities almost drove the sperm whale to extinction from hunting. After the ban on hunting, there is a niche in the global market for biolubricants with properties similar to spermaceti. Wax esters can also serve as a mechanism for producing insect sex pheromone fatty alcohols. Pheromone-based mating disruption strategies are in high demand to replace the toxic pesticides in agriculture and manage insect plagues threatening our food and fiber reserves. In this study we set out to investigate the possibilities of in planta assembly of wax esters, for specific applications, through transient expression of various mix-and-match combinations of genes in Nicotiana benthamiana leaves. Our synthetic biology designs were outlined in order to pivot plant lipid metabolism into producing wax esters with targeted fatty acyl and fatty alcohols moieties. Through this approach we managed to obtain industrially important spermaceti-like wax esters enriched in medium-chain fatty acyl and/or fatty alcohol moieties of wax esters. Via employment of plant codon-optimized moth acyl-CoA desaturases we also managed to capture unusual, unsaturated fatty alcohol and fatty acyl moieties, structurally similar to moth pheromone compounds, in plant-accumulated wax esters. Comparison between outcomes of different experimental designs identified targets for stable transformation to accumulate specialized wax esters and helped us to recognize possible bottlenecks of such accumulation.
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14.
  • Englund, Elias, et al. (författare)
  • Systematic overexpression study to find target enzymes enhancing production of terpenes in Synechocystis PCC 6803, using isoprene as a model compound
  • 2018
  • Ingår i: Metabolic engineering. - : Academic Press Inc.. - 1096-7176 .- 1096-7184. ; 49, s. 164-177
  • Tidskriftsartikel (refereegranskat)abstract
    • Of the two natural metabolic pathways for making terpenoids, biotechnological utilization of the mevalonate (MVA) pathway has enabled commercial production of valuable compounds, while the more recently discovered but stoichiometrically more efficient methylerythritol phosphate (MEP) pathway is underdeveloped. We conducted a study on the overexpression of each enzyme in the MEP pathway in the unicellular cyanobacterium Synechocystis sp. PCC 6803, to identify potential targets for increasing flux towards terpenoid production, using isoprene as a reporter molecule. Results showed that the enzymes Ipi, Dxs and IspD had the biggest impact on isoprene production. By combining and creating operons out of those genes, isoprene production was increased 2-fold compared to the base strain. A genome-scale model was used to identify targets upstream of the MEP pathway that could redirect flux towards terpenoids. A total of ten reactions from the Calvin-Benson-Bassham cycle, lower glycolysis and co-factor synthesis pathways were probed for their effect on isoprene synthesis by co-expressing them with the MEP enzymes, resulting in a 60% increase in production from the best strain. Lastly, we studied two isoprene synthases with the highest reported catalytic rates. Only by expressing them together with Dxs and Ipi could we get stable strains that produced 2.8 mg/g isoprene per dry cell weight, a 40-fold improvement compared to the initial strain. 
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15.
  • Fletcher, Eugene, 1986, et al. (författare)
  • Evolutionary engineering reveals divergent paths when yeast is adapted to different acidic environments
  • 2017
  • Ingår i: Metabolic engineering. - : Academic Press. - 1096-7176 .- 1096-7184. ; 39, s. 19-28
  • Tidskriftsartikel (refereegranskat)abstract
    • Tolerance of yeast to acid stress is important for many industrial processes including organic acid production. Therefore, elucidating the molecular basis of long term adaptation to acidic environments will be beneficial for engineering production strains to thrive under such harsh conditions. Previous studies using gene expression analysis have suggested that both organic and inorganic acids display similar responses during short term exposure to acidic conditions. However, biological mechanisms that will lead to long term adaptation of yeast to acidic conditions remains unknown and whether these mechanisms will be similar for tolerance to both organic and inorganic acids is yet to be explored. We therefore evolved Saccharomyces cerevisiae to acquire tolerance to HCl (inorganic acid) and to 0.3 M L-lactic acid (organic acid) at pH 2.8 and then isolated several low pH tolerant strains. Whole genome sequencing and RNA-seq analysis of the evolved strains revealed different sets of genome alterations suggesting a divergence in adaptation to these two acids. An altered sterol composition and impaired iron uptake contributed to HCl tolerance whereas the formation of a multicellular morphology and rapid lactate degradation was crucial for tolerance to high concentrations of lactic acid. Our findings highlight the contribution of both the selection pressure and nature of the acid as a driver for directing the evolutionary path towards tolerance to low pH. The choice of carbon source was also an important factor in the evolutionary process since cells evolved on two different carbon sources (raffinose and glucose) generated a different set of mutations in response to the presence of lactic acid. Therefore, different strategies are required for a rational design of low pH tolerant strains depending on the acid of interest.
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16.
  • Gatto, Francesco, 1987, et al. (författare)
  • Pan-cancer analysis of the metabolic reaction network
  • 2020
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 57, s. 51-62
  • Tidskriftsartikel (refereegranskat)abstract
    • Metabolic reprogramming is considered a hallmark of malignant transformation. However, it is not clear whether the network of metabolic reactions expressed by cancers of different origin differ from each other or from normal human tissues. In this study, we reconstructed functional and connected genome-scale metabolic models for 917 primary tumor samples across 13 types based on the probability of expression for 3765 reference metabolic genes in the sample. This network-centric approach revealed that tumor metabolic networks are largely similar in terms of accounted reactions, despite diversity in the expression of the associated genes. On average, each network contained 4721 reactions, of which 74% were core reactions (present in >95% of all models). Whilst 99.3% of the core reactions were classified as housekeeping also in normal tissues, we identified reactions catalyzed by ARG2, RHAG, SLC6 and SLC16 family gene members, and PTGS1 and PTGS2 as core exclusively in cancer. These findings were subsequently replicated in an independent validation set of 3388 genome-scale metabolic models. The remaining 26% of the reactions were contextual reactions. Their inclusion was dependent in one case (GLS2) on the absence of TP53 mutations and in 94.6% of cases on differences in cancer types. This dependency largely resembled differences in expression patterns in the corresponding normal tissues, with some exceptions like the presence of the NANP-encoded reaction in tumors not from the female reproductive system or of the SLC5A9-encoded reaction in kidney-pancreatic-colorectal tumors. In conclusion, tumors expressed a metabolic network virtually overlapping the matched normal tissues, raising the possibility that metabolic reprogramming simply reflects cancer cell plasticity to adapt to varying conditions thanks to redundancy and complexity of the underlying metabolic networks. At the same time, the here uncovered exceptions represent a resource to identify selective liabilities of tumor metabolism.
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17.
  • Grotkjær, Thomas, et al. (författare)
  • Comparative metabolic network analysis of two xylose fermenting recombinant Saccharomyces cerevisiae strains
  • 2005
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 7:5-6, s. 437-444
  • Tidskriftsartikel (refereegranskat)abstract
    • The recombinant xylose fermenting strain Saccharomyces cerevisiae TMB3001 can grow on xylose, but the xylose utilisation rate is low. One important reason for the inefficient fermentation of xylose to ethanol is believed to be the imbalance of redox co-factors. In the present study, a metabolic flux model was constructed for two recombinant S. cerevisiae strains: TMB3001 and CPB.CR4 which in addition to xylose metabolism have a modulated redox metabolism, i.e. ammonia assimilation was shifted from being NADPH to NADH dependent by deletion of gdh1 and over-expression of GDH2. The intracellular fluxes were estimated for both strains in anaerobic continuous cultivations when the growth limiting feed consisted of glucose (2.5 g L−1) and xylose (13 g L−1). The metabolic network analysis with 13C labelled glucose showed that there was a shift in the specific xylose reductase activity towards use of NADH as co-factor rather than NADPH. This shift is beneficial for solving the redox imbalance and it can therefore partly explain the 25% increase in the ethanol yield observed for CPB.CR4. Furthermore, the analysis indicated that the glyoxylate cycle was activated in CPB.CR4.
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18.
  • Headman Van Vleet, Jennifer, et al. (författare)
  • Deleting the para-nitrophenyl phosphatase (pNPPase), PHO13, in recombinant Saccharomyces cerevisiae improves growth and ethanol production on D-xylose
  • 2008
  • Ingår i: Metabolic Engineering. - 1096-7176 .- 1096-7184. ; :10, s. 360-369
  • Tidskriftsartikel (refereegranskat)abstract
    • Overexpression of D-xylulokinase in Saccharomyces cerevisiae engineered for assimilation of xylose results in growth inhibition that is more pronounced at higher xylose concentrations. Mutants deficient in the para-nitrophenyl phosphatase, PHO13, resist growth inhibition on xylose. We studied this inhibition under aerobic growth conditions in well-controlled bioreactors using engineered S. cerevisiae CEN.PK. Growth on glucose was not significantly affected in pho13∆ mutants, but acetate production increased by 75%. Cell growth, ethanol production, and xylose consumption all increased markedly in pho13∆ mutants. The specific growth rate and rate of specific xylose uptake were approximately 1.5 times higher in the deletion strain than in the parental strain when growing on glucose-xylose mixtures and up to 10-fold higher when growing on xylose alone. In addition to showing higher acetate levels, pho13∆ mutants also produced less glycerol on xylose, suggesting that deletion of Pho13p could improve growth by altering redox levels when cells are grown on xylose.
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19.
  • Hellgren, John, 1991, et al. (författare)
  • Promiscuous phosphoketolase and metabolic rewiring enables novel non-oxidative glycolysis in yeast for high-yield production of acetyl-CoA derived products
  • 2020
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 62, s. 150-160
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon-conserving pathways have the potential of increasing product yields in biotechnological processes. The aim of this project was to investigate the functionality of a novel carbon-conserving pathway that produces 3 mol of acetyl-CoA from fructose-6-phosphate without carbon loss in the yeast Saccharomyces cerevisiae. This cyclic pathway relies on a generalist phosphoketolase (Xfspk), which can convert xylulose-5-phosphate, fructose-6-phosphate and sedoheptulose-7-phosphate (S7P) to acetyl phosphate. This cycle is proposed to overcome bottlenecks from the previously reported non-oxidative glycolysis (NOG) cycle. Here, in silico simulations showed accumulation of S7P in the NOG cycle, which was resolved by blocking the non-oxidative pentose phosphate pathway and introducing Xfspk and part of the riboneogenesis pathway. To implement this, a transketolase and transaldolase deficient S. cerevisiae was generated and a cyclic pathway, the Glycolysis AlTernative High Carbon Yield Cycle (GATHCYC), was enabled through xfspk expression and sedoheptulose bisphosphatase (SHB17) overexpression. Flux through the GATHCYC was demonstrated in vitro with a phosphoketolase assay on crude cell free extracts, and in vivo by constructing a strain that was dependent on a functional pathway to survive. Finally, we showed that introducing the GATHCYC as a carbon-conserving route for 3-hydroxypropionic acid (3-HP) production resulted in a 109% increase in 3-HP titers when the glucose was exhausted compared to the phosphoketolase route only.
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20.
  • Hing, Nathaphon Yu King, et al. (författare)
  • Combining isotopically non-stationary metabolic flux analysis with proteomics to unravel the regulation of the Calvin-Benson-Bassham cycle in Synechocystis sp. PCC 6803
  • 2019
  • Ingår i: Metabolic engineering. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 1096-7176 .- 1096-7184. ; 56, s. 77-84
  • Tidskriftsartikel (refereegranskat)abstract
    • Photosynthetic microorganisms are increasingly being investigated as a sustainable alternative to existing bio-industrial processes, converting CO2 into desirable end products without the use of carbohydrate feedstock. The Calvin-Benson-Bassham (CBB) cycle is the main pathway of carbon fixation metabolism in photosynthetic organisms. In this study, we analyzed the metabolic fluxes in two strains of the unicellular cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis) that overexpressed fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) and transketolase (TK), respectively. These two potential carbon flux control enzymes in the CBB cycle had previously been shown to improve biomass accumulation when overexpressed under air and low light (15 mu mol m(-2) s(-1)) conditions (Liang and Lindblad, 2016). We measured the growth rates of Synechocystis under atmospheric and high (3% v/v) CO2 conditions at 80 mu mol m(-2) s(-1). Surprisingly, the cells overexpressing transketolase (tktA) demonstrated no significant increase in growth rates when CO2 was increased, suggesting an altered carbon flux distribution and a potential metabolic bottleneck in carbon fixation. Moreover, the tktA strain had an increased susceptibility to oxidative stress under high light as revealed by its chlorotic phenotype under high light conditions. In contrast, the fructose-1,6/sedoheptulose-1,7-bisphosphatase (70glpX) and wildtype cells demonstrated increases in growth rates as expected. To investigate the disparate phenotypical responses of these different Synechocystis strains, isotopically non-stationary metabolic flux analysis (INST-MFA) was used to estimate the carbon flux distribution of tktA, 70glpX, and a kanamycin-resistant control (Km), under atmospheric conditions. In addition, untargeted label-free proteomics, which can detect changes in relative enzymatic abundance, was employed to study the possible effects caused by overexpressing each enzyme. Fluxomic and proteomic results indicated a decrease in oxidative pentose phosphate pathway activity when either FBP/SBPase or TK were overexpressed, resulting in increased carbon fixation efficiency. These results are an example of the integration of multiple omic-level experimental techniques and can be used to guide future metabolic engineering efforts to improve performances and efficiencies.
  •  
21.
  • Hofmann, G., et al. (författare)
  • Recombinant bacterial hemoglobin alters metabolism of Aspergillus niger
  • 2009
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 11:1, s. 8-12
  • Tidskriftsartikel (refereegranskat)abstract
    • The filamentous fungus Aspergillus niger is used extensively for the production of enzymes and organic acids. A major problem in industrial fermentations with this fungus is to ensure sufficient supply of oxygen required for respiratory metabolism of the fungus. In case of oxygen limitation, the fungus will produce various by-products like organic acids and polyols. In order to circumvent this problem we here study the effects of the expression of a bacterial hemoglobin protein on the metabolism of A. niger. We integrated the vgb gene from Vitreoscilla sp. into the genome at the pyrA locus behind the strong gpdA promoter from Aspergillus nidulans. Analysis of secreted metabolites, oxygen uptake, CO2 evolution and biomass formation points towards a relief of stress in the mutant expressing VHB when it is exposed to oxygen limitation. Our findings therefore point to an interesting strategy to attenuate unwanted side effects resulting from oxygen limitation during industrial fermentations with A. niger. (C) 2008 Elsevier Inc. All rights reserved.
  •  
22.
  • Hong, Kuk-ki, 1976, et al. (författare)
  • Adaptively evolved yeast mutants on galactose show trade-offs in carbon utilization on glucose
  • 2013
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 16:1, s. 78-86
  • Tidskriftsartikel (refereegranskat)abstract
    • Adaptive evolution offers many opportunities in metabolic engineering; however, several constraints still exist as evolutionary trade-offs may impose collateral cost to obtain new traits. The application of adaptive evolution for strains development could be further improved by elucidating the molecular mechanisms. In this study, adaptively evolved yeast mutants with improved galactose utilization ability showed impaired glucose utilization. The molecular genetic basis of this trade-off was investigated using a systems biology approach. Transcriptional and metabolic changes resulting from the improvement of galactose utilization were found maintained during growth on glucose. Moreover, glucose repression related genes showed conserved expression patterns during growth on both sugars. Mutations in the RAS2 gene that were identified as beneficial for galactose utilization in evolved mutants exhibited significant correlation with attenuation of glucose utilization. These results indicate that antagonistic pleiotropy is the dominant mechanism in the observed trade-off, and it is likely realized by changes in glucose signaling.
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23.
  • Hou, Jin, 1982, et al. (författare)
  • Engineering of vesicle trafficking improves heterologous protein secretion in Saccharomyces cerevisiae
  • 2012
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 14:2, s. 120-127
  • Tidskriftsartikel (refereegranskat)abstract
    • The yeast Saccharomyces cerevisiae is a widely used platform for the production of heterologous proteins of medical or industrial interest. However, heterologous protein productivity is often restricted due to the limitations of the host strain. In the protein secretory pathway, the protein trafficking between different organelles is catalyzed by the soluble NSF (N-ethylmaleimide-sensitive factor) receptor (SNARE) complex and regulated by the Secl/Munc18 (SM) proteins. In this study, we report that over-expression of the SM protein encoding genes SEC1 and SLY1, improves the protein secretion in S. cerevisiae. Engineering Sec1p, the SM protein that is involved in vesicle trafficking from Golgi to cell membrane, improves the secretion of heterologous proteins human insulin precursor and alpha-amylase, and also the secretion of an endogenous protein invertase. Enhancing Sly1p, the SM protein regulating the vesicle fusion from endoplasmic reticulum (ER) to Golgi, increases alpha-amylase production only. Our study demonstrates that strengthening the protein trafficking in ER-to-Golgi and Golgi-to-plasma membrane process is a novel secretory engineering strategy for improving heterologous protein production in S. cerevisiae.
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24.
  • Hou, J., et al. (författare)
  • Metabolic impact of redox cofactor perturbations in Saccharomyces cerevisiae
  • 2009
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 11:4-5, s. 253-261
  • Tidskriftsartikel (refereegranskat)abstract
    • Redox cofactors play a pivotal role in coupling catabolism with anabolism and energy generation during metabolism. There exists a delicate balance in the intracellular level of these cofactors to ascertain an optimal metabolic output. Therefore, cofactors are emerging to be attractive targets to induce widespread changes in metabolism. We present a detailed analysis of the impact of perturbations in redox cofactors in the cytosol or mitochondria on glucose and energy metabolism in Saccharomyces cerevisiae to aid metabolic engineering decisions that involve cofactor engineering. We enhanced NADH oxidation by introducing NADH oxidase or alternative oxidase, its ATP-mediated conversion to NADPH using NADH kinase as well as the interconversion of NADH and NADPH independent of ATP by the soluble, non-proton-translocating bacterial transhydrogenase. Decreasing cytosolic NADH level lowered glycerol production, while decreasing mitochondrial NADH lowered ethanol production. However, when these reactions were coupled with NADPH production, the metabolic changes were more moderated. The direct consequence of these perturbations could be seen in the shift of the intracellular concentrations of the cofactors. The changes in product profile and intracellular metabolite levels were closely linked to the ATP requirement for biomass synthesis and the efficiency of oxidative phosphorylation, as estimated from a simple stoichiometric model. The results presented here will provide valuable insights for a quantitative understanding and prediction of cellular response to redox-based perturbations for metabolic engineering applications. (C) 2009 Elsevier Inc. All rights reserved.
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25.
  • Hou, Jianshen, et al. (författare)
  • Rewiring carbon flux in Escherichia coli using a bifunctional molecular switch
  • 2020
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 61, s. 47-57
  • Tidskriftsartikel (refereegranskat)abstract
    • The unbalanced distribution of carbon flux in microbial cell factories can lead to inefficient production and poor cell growth. Uncoupling cell growth and chemical synthesis can therefore improve microbial cell factory efficiency. Such uncoupling, which requires precise manipulation of carbon fluxes, can be achieved by up-regulating or down-regulating the expression of enzymes of various pathways. In this study, a dynamic turn-off switch (dTFS) and a dynamic turn-on switch (dTNS) were constructed using growth phase-dependent promoters and degrons. By combining the dTFS and dTNS, a bifunctional molecular switch that could orthogonally regulate two target proteins was introduced. This bifunctional molecular switch was used to uncouple cell growth from shikimic acid and D-glucaric acid synthesis, resulting in the production of 14.33 g/L shikimic acid and the highest reported productivity of D-glucaric acid (0.0325 g/L/h) in Escherichia coli MG1655. This proved that the bifunctional molecular switch could rewire carbon fluxes by controlling target protein abundance.
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26.
  • Hu, Yating, 1991, et al. (författare)
  • Heterologous transporter expression for improved fatty alcohol secretion in yeast
  • 2018
  • Ingår i: Metabolic engineering. - : Academic Press. - 1096-7176 .- 1096-7184. ; 45, s. 51-58
  • Tidskriftsartikel (refereegranskat)abstract
    • The yeast Saccharomyces cerevisiae is an attractive host for industrial scale production of biofuels including fatty alcohols due to its robustness and tolerance towards harsh fermentation conditions. Many metabolic engineering strategies have been applied to generate high fatty alcohol production strains. However, impaired growth caused by fatty alcohol accumulation and high cost of extraction are factors limiting large-scale production. Here, we demonstrate that the use of heterologous transporters is a promising strategy to increase fatty alcohol production. Among several plant and mammalian transporters tested, human FATP1 was shown to mediate fatty alcohol export in a high fatty alcohol production yeast strain. An approximately five-fold increase of fatty alcohol secretion was achieved. The results indicate that the overall cell fitness benefited from fatty alcohol secretion and that the acyl-CoA synthase activity of FATP1 contributed to increased cell growth as well. This is the first study that enabled an increased cell fitness for fatty alcohol production by heterologous transporter expression in yeast, and this investigation indicates a new potential function of FATP1, which has been known as a free fatty acid importer to date. We furthermore successfully identified the functional domain of FATP1 involved in fatty alcohol export through domain exchange between FATP1 and another transporter, FATP4. This study may facilitate a successful commercialization of fatty alcohol production in yeast and inspire the design of novel cell factories.
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27.
  •  
28.
  • Ishchuk, Olena, 1980, et al. (författare)
  • Improved production of human hemoglobin in yeast by engineering hemoglobin degradation
  • 2021
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 66, s. 259-267
  • Tidskriftsartikel (refereegranskat)abstract
    • With the increasing demand for blood transfusions, the production of human hemoglobin (Hb) from sustainable sources is increasingly studied. Microbial production is an attractive option, as it may provide a cheap, safe, and reliable source of this protein. To increase the production of human hemoglobin by the yeast Saccharomyces cerevisiae, the degradation of Hb was reduced through several approaches. The deletion of the genes HMX1 (encoding heme oxygenase), VPS10 (encoding receptor for vacuolar proteases), PEP4 (encoding vacuolar proteinase A), ROX1 (encoding heme-dependent repressor of hypoxic genes) and the overexpression of the HEM3 (encoding porphobilinogen deaminase) and the AHSP (encoding human alpha-hemoglobin-stabilizing protein) genes — these changes reduced heme and Hb degradation and improved heme and Hb production. The reduced hemoglobin degradation was validated by a bilirubin biosensor. During glucose fermentation, the engineered strains produced 18% of intracellular Hb relative to the total yeast protein, which is the highest production of human hemoglobin reported in yeast. This increased hemoglobin production was accompanied with an increased oxygen consumption rate and an increased glycerol yield, which (we speculate) is the yeast's response to rebalance its NADH levels under conditions of oxygen limitation and increased protein-production.
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29.
  • Janasch, Markus, et al. (författare)
  • Thermodynamic limitations of PHB production from formate and fructose in Cupriavidus necator
  • 2022
  • Ingår i: Metabolic engineering. - Elsevier BV : Elsevier BV. - 1096-7176 .- 1096-7184. ; 73, s. 256-269
  • Tidskriftsartikel (refereegranskat)abstract
    • The chemolithotroph Cupriavidus necator H16 is known as a natural producer of the bioplastic-polymer PHB, as well as for its metabolic versatility to utilize different substrates, including formate as the sole carbon and energy source. Depending on the entry point of the substrate, this versatility requires adjustment of the thermodynamic landscape to maintain sufficiently high driving forces for biological processes. Here we employed a model of the core metabolism of C. necator H16 to analyze the thermodynamic driving forces and PHB yields from formate for different metabolic engineering strategies. For this, we enumerated elementary flux modes (EFMs) of the network and evaluated their PHB yields as well as thermodynamics via Max-min driving force (MDF) analysis and random sampling of driving forces. A heterologous ATP:citrate lyase reaction was predicted to increase driving force for producing acetyl-CoA. A heterologous phosphoketolase reaction was predicted to increase maximal PHB yields as well as driving forces. These enzymes were then verified experimentally to enhance PHB titers between 60 and 300% in select conditions. The EFM analysis also revealed that PHB production from formate may be limited by low driving forces through citrate lyase and aconitase, as well as cofactor balancing, and identified additional reactions associated with low and high PHB yield. Proteomics analysis of the engineered strains confirmed an increased abundance of aconitase and cofactor balancing. The findings of this study aid in understanding metabolic adaptation. Furthermore, the outlined approach will be useful in designing metabolic engineering strategies in other non-model bacteria.
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30.
  • Kaczmarzyk, Danuta, et al. (författare)
  • Diversion of the long-chain acyl-ACP pool in Synechocystis to fatty alcohols through CRISPRi repression of the essential phosphate acyltransferase PlsX
  • 2018
  • Ingår i: Metabolic engineering. - : Academic Press. - 1096-7176 .- 1096-7184. ; 45, s. 59-66
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatty alcohol production in Synechocystis sp. PCC 6803 was achieved through heterologous expression of the fatty acyl-CoA/ACP reductase Maqu2220 from the bacteria Marinobacter aquaeolei VT8 and the fatty acyl-ACP reductase DPW from the rice Oryza sativa. These platform strains became models for testing multiplex CRISPR-interference (CRISPRi) metabolic engineering strategies to both improve fatty alcohol production and to study membrane homeostasis. CRISPRi allowed partial repression of up to six genes simultaneously, each encoding enzymes of acyl-ACP-consuming pathways. We identified the essential phosphate acyltransferase enzyme PlsX (slr1510) as a key node in C18 fatty acyl-ACP consumption, repression of slr1510 increased octadecanol productivity threefold over the base strain and gave the highest specific titers reported for this host, 10.3 mg g−1 DCW. PlsX catalyzes the first committed step of phosphatidic acid synthesis, and has not been characterized in Synechocystis previously. We found that accumulation of fatty alcohols impaired growth, altered the membrane composition, and caused a build-up of reactive oxygen species.
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31.
  • Kildegaard, Kanchana R., et al. (författare)
  • Evolution reveals a glutathione-dependent mechanism of 3-hydroxypropionic acid tolerance
  • 2014
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 26, s. 57-66
  • Tidskriftsartikel (refereegranskat)abstract
    • Biologically produced 3-hydroxypropionic acid (3HP) is a potential source for sustainable acrylates and can also find direct use as monomer in the production of biodegradable polymers. For industrial scale production there is a need for robust cell factories tolerant to high concentration of 3HP, preferably at low pH. Through adaptive laboratory evolution we selected S. cerevisiae strains with improved tolerance to 3HP at pH 3.5. Genome sequencing followed by functional analysis identified the causal mutation in SFA1 gene encoding S-(hyclroxymerhyl)glutathione dehydrogenase. Based on our findings, we propose that 3HP toxicity is mediated by 3-hydroxypropionic aldehyde (reuterin ) and that glutathione-dependent reactions are used for reuterin detoxification. The identified molecular response to 3HP and reuterin may well be a general mechanism for handling resistance to organic acid and aldehydes by living cells. (C) 2014 International Metabolic Engineering Society Published by Elsevier Inc. On behalf of International Metabolic Engineering Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/)
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32.
  • Krivoruchko, Anastasia, 1984, et al. (författare)
  • Microbial acetyl-CoA metabolism and metabolic engineering
  • 2015
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 28, s. 28-42
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Recent concerns over the sustainability of petrochemical-based processes for production of desired chemicals have fueled research into alternative modes of production. Metabolic engineering of microbial cell factories such as Saccharomyces cerevisiae and Escherichia coli offers a sustainable and flexible alternative for the production of various molecules. Acetyl-CoA is a key molecule in microbial central carbon metabolism and is involved in a variety of cellular processes. In addition, it functions as a precursor for many molecules of biotechnological relevance. Therefore, much interest exists in engineering the metabolism around the acetyl-CoA pools in cells in order to increase product titers. Here we provide an overview of the acetyl-CoA metabolism in eukaryotic and prokaryotic microbes (with a focus on S. cerevisiae and E. coli), with an emphasis on reactions involved in the production and consumption of acetyl-CoA. In addition, we review various strategies that have been used to increase acetyl-CoA production in these microbes.
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33.
  • Kugler, Amit, et al. (författare)
  • Machine learning predicts system-wide metabolic flux control in cyanobacteria
  • 2024
  • Ingår i: Metabolic engineering. - : Elsevier. - 1096-7176 .- 1096-7184. ; 82, s. 171-182
  • Tidskriftsartikel (refereegranskat)abstract
    • Metabolic fluxes and their control mechanisms are fundamental in cellular metabolism, offering insights for the study of biological systems and biotechnological applications. However, quantitative and predictive understanding of controlling biochemical reactions in microbial cell factories, especially at the system level, is limited. In this work, we present ARCTICA, a computational framework that integrates constraint-based modelling with machine learning tools to address this challenge. Using the model cyanobacterium Synechocystis sp. PCC 6803 as chassis, we demonstrate that ARCTICA effectively simulates global-scale metabolic flux control. Key findings are that (i) the photosynthetic bioproduction is mainly governed by enzymes within the Calvin-Benson-Bassham (CBB) cycle, rather than by those involve in the biosynthesis of the end-product, (ii) the catalytic capacity of the CBB cycle limits the photosynthetic activity and downstream pathways and (iii) ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is a major, but not the most, limiting step within the CBB cycle. Predicted metabolic reactions qualitatively align with prior experimental observations, validating our modelling approach. ARCTICA serves as a valuable pipeline for understanding cellular physiology and predicting rate-limiting steps in genome-scale metabolic networks, and thus provides guidance for bioengineering of cyanobacteria.
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34.
  • Kukil, Kateryna, et al. (författare)
  • Laboratory evolution of Synechocystis sp. PCC 6803 for phenylpropanoid production
  • 2023
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 79, s. 27-37
  • Tidskriftsartikel (refereegranskat)abstract
    • Cyanobacteria are promising as a biotechnological platform for production of various industrially relevant compounds, including aromatic amino acids and their derivatives, phenylpropanoids. In this study, we have generated phenylalanine resistant mutant strains (PRMs) of the unicellular cyanobacterium Synechocystis sp. PCC 6803, by laboratory evolution under the selective pressure of phenylalanine, which inhibits the growth of wild type Synechocystis. The new strains of Synechocystis were tested for their ability to secrete phenylalanine in the growth medium during cultivation in shake flasks as well as in a high-density cultivation (HDC) system. All PRM strains secreted phenylalanine into the culture medium, with one of the mutants, PRM8, demonstrating the highest specific production of 24.9 ± 7 mg L−1·OD750−1 or 610 ± 196 mg L−1 phenylalanine after four days of growth in HDC. We further overexpressed phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) in the mutant strains in order to determine the potential of PRMs for production of trans-cinnamic acid (tCA) and para-coumaric acid (pCou), the first intermediates of the plant phenylpropanoid pathway. Productivities of these compounds were found to be lower in the PRMs compared to respective control strains, except for PRM8 under HDC conditions. The PRM8 background strain in combination with PAL or TAL expression demonstrated a specific production of 52.7 ± 15 mg L−1·OD750−1 tCA and 47.1 ± 7 mg L−1·OD750−1 pCou, respectively, with a volumetric titer reaching above 1 g L−1 for both products after four days of HDC cultivation. The genomes of PRMs were sequenced in order to identify which mutations caused the phenotype. Interestingly, all of the PRMs contained at least one mutation in their ccmA gene, which encodes DAHP synthase, the first enzyme of the pathway for aromatic amino acids biosynthesis. Altogether, we demonstrate that the combination of laboratory-evolved mutants and targeted metabolic engineering can be a powerful tool in cyanobacterial strain development.
  •  
35.
  • Kumar, Manish, 1982, et al. (författare)
  • Gut microbiota dysbiosis is associated with malnutrition and reduced plasma amino acid levels: Lessons from genome-scale metabolic modeling
  • 2018
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 49, s. 128-142
  • Tidskriftsartikel (refereegranskat)abstract
    • Malnutrition is a severe non-communicable disease, which is prevalent in children from low-income countries. Recently, a number of metagenomics studies have illustrated associations between the altered gut microbiota and child malnutrition. However, these studies did not examine metabolic functions and interactions between individual species in the gut microbiota during health and malnutrition. Here, we applied genome-scale metabolic modeling to model the gut microbial species, which were selected from healthy and malnourished children from three countries. Our analysis showed reduced metabolite production capabilities in children from two lowincome countries compared with a high-income country. Additionally, the models were also used to predict the community-level metabolic potentials of gut microbes and the patterns of pairwise interactions among species. Hereby we found that due to bacterial interactions there may be reduced production of certain amino acids in malnourished children compared with healthy children from the same communities. To gain insight into alterations in the metabolism of malnourished (stunted) children, we also performed targeted plasma metabolic profiling in the first 2 years of life of 25 healthy and 25 stunted children. Plasma metabolic profiling further revealed that stunted children had reduced plasma levels of essential amino acids compared to healthy controls. Our analyses provide a framework for future efforts towards further characterization of gut microbial metabolic capabilities and their contribution to malnutrition.
  •  
36.
  • Li, M., et al. (författare)
  • De novo production of resveratrol from glucose or ethanol by engineered Saccharomyces cerevisiae
  • 2015
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 32, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Resveratrol is a natural antioxidant compound, used as food supplement and cosmetic ingredient. Microbial production of resveratrol has until now been achieved by supplementation of expensive substrates, p-coumaric acid or aromatic amino acids. Here we engineered the yeast Saccharomyces cerevisiae to produce resveratrol directly from glucose or ethanol via tyrosine intermediate. First we introduced the biosynthetic pathway, consisting of tyrosine ammonia-lyase from Herpetosiphon aurantiacus, 4-coumaryl-CoA ligase from Arabidopsis thaliana and resveratrol synthase from Vitis vinifera, and obtained 2.73±0.05mgL-1 resveratrol from glucose. Then we over-expressed feedback-insensitive alleles of ARO4 encoding 3-deoxy-D-arabino-heptulosonate-7-phosphate and ARO7 encoding chorismate mutase, resulting in production of 4.85±0.31mgL-1 resveratrol from glucose as the sole carbon source. Next we improved the supply of the precursor malonyl-CoA by over-expressing a post-translational de-regulated version of the acetyl-CoA carboxylase encoding gene ACC1; this strategy further increased resveratrol production to 6.39±0.03mgL-1. Subsequently, we improved the strain by performing multiple-integration of pathway genes resulting in resveratrol production of 235.57±7.00mgL-1. Finally, fed-batch fermentation of the final strain with glucose or ethanol as carbon source resulted in a resveratrol titer of 415.65 and 531.41mgL-1, respectively.
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37.
  • Li, Peishun, 1988, et al. (författare)
  • Metabolic engineering of human gut microbiome: Recent developments and future perspectives
  • 2023
  • Ingår i: Metabolic Engineering. - 1096-7176 .- 1096-7184. ; 79, s. 1-13
  • Forskningsöversikt (refereegranskat)abstract
    • Many studies have demonstrated that the gut microbiota is associated with human health and disease. Manipulation of the gut microbiota, e.g. supplementation of probiotics, has been suggested to be feasible, but subject to limited therapeutic efficacy. To develop efficient microbiota-targeted diagnostic and therapeutic strategies, metabolic engineering has been applied to construct genetically modified probiotics and synthetic microbial consortia. This review mainly discusses commonly adopted strategies for metabolic engineering in the human gut microbiome, including the use of in silico, in vitro, or in vivo approaches for iterative design and construction of engineered probiotics or microbial consortia. Especially, we highlight how genome-scale metabolic models can be applied to advance our understanding of the gut microbiota. Also, we review the recent applications of metabolic engineering in gut microbiome studies as well as discuss important challenges and opportunities.
  •  
38.
  • Liang, Feiyan, et al. (författare)
  • Effects of overexpressing photosynthetic carbon flux control enzymes in the cyanobacterium Synechocystis PCC 6803
  • 2016
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 38, s. 56-64
  • Tidskriftsartikel (refereegranskat)abstract
    • Synechocystis PCC 6803 is a model unicellular cyanobacterium used in e.g. photosynthesis and CO2 assimilation research. In the present study we examined the effects of overexpressing Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), sedoheptulose 1,7-biphosphatase (SBPase), fructose-bisphosphate aldolase (FBA) and transketolase (TK), confirmed carbon flux control enzymes of the Calvin-Bassham-Benson (CBB) cycle in higher plants, in Synechocystis PCC 6803. Overexpressing RuBisCO, SBPase and FBA resulted in increased in vivo oxygen evolution (maximal 115%), growth rate and biomass accumulation (maximal 52%) under 100μmolphotonsm(-2)s(-1) light condition. Cells overexpressing TK showed a chlorotic phenotype but increased biomass by approximately 42% under 100μmolphotonsm(-2)s(-1) light condition. Under 15μmolphotonsm(-2)s(-1) light condition, cells overexpressing TK showed enhanced in vivo oxygen evolution. This study demonstrates increased growth and biomass accumulation when overexpressing selected enzymes of the CBB cycle. RuBisCO, SBPase, FBA and TK are identified as four potential targets to improve growth and subsequently also yield of valuable products from Synechocystis PCC 6803.
  •  
39.
  • Liang, Feiyan, et al. (författare)
  • Engineered cyanobacteria with enhanced growth show increased ethanol production and higher biofuel to biomass ratio
  • 2018
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 46, s. 51-59
  • Tidskriftsartikel (refereegranskat)abstract
    • The Calvin-Benson-Bassham (CBB) cycle is the main pathway to fix atmospheric CO2 and store energy in carbon bonds, forming the precursors of most primary and secondary metabolites necessary for life. Speeding up the CBB cycle theoretically has positive effects on the subsequent growth and/or the end metabolite(s) production. Four CBB cycle enzymes, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase), transketolase (TK) and aldolase (FBA) were selected to be co-overexpressed with the ethanol synthesis enzymes pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) in the cyanobacterium Synechocystis PCC 6803. An inducible promoter, PnrsB, was used to drive PDC and ADH expression. When PnrsB was induced and cells were cultivated at 65 µmol photons m−2 s−1, the RuBisCO-, FBP/SBPase-, TK-, and FBA-expressing strains produced 55%, 67%, 37% and 69% more ethanol and 7.7%, 15.1%, 8.8% and 10.1% more total biomass (the sum of dry cell weight and ethanol), respectively, compared to the strain only expressing the ethanol biosynthesis pathway. The ethanol to total biomass ratio was also increased in CBB cycle enzymes overexpressing strains. This study experimentally demonstrates that using the cells with enhanced carbon fixation, when the product synthesis pathway is not the main bottleneck, can significantly increase the generation of a product (exemplified with ethanol), which acts as a carbon sink.
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40.
  • Lindberg, Pia, et al. (författare)
  • Engineering a platform for photosynthetic isoprene production in cyanobacteria, using Synechocystis as the model organism.
  • 2010
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 12:1, s. 70-9
  • Tidskriftsartikel (refereegranskat)abstract
    • The concept of "photosynthetic biofuels" envisions application of a single organism, acting both as photo-catalyst and producer of ready-made fuel. This concept was applied upon genetic engineering of the cyanobacterium Synechocystis, conferring the ability to generate volatile isoprene hydrocarbons from CO(2) and H(2)O. Heterologous expression of the Pueraria montana (kudzu) isoprene synthase (IspS) gene in Synechocystis enabled photosynthetic isoprene generation in these cyanobacteria. Codon-use optimization of the kudzu IspS gene improved expression of the isoprene synthase in Synechocystis. Use of the photosynthesis psbA2 promoter, to drive the expression of the IspS gene, resulted in a light-intensity-dependent isoprene synthase expression. Results showed that oxygenic photosynthesis can be re-directed to generate useful small volatile hydrocarbons, while consuming CO(2), without a prior requirement for the harvesting, dewatering and processing of the respective biomass.
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41.
  • Liu, Lifang, 1979, et al. (författare)
  • Balanced globin protein expression and heme biosynthesis improve production of human hemoglobin in Saccharomyces cerevisiae
  • 2014
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 21, s. 9-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to limitations associated with whole blood for transfusions (antigen compatibility, transmission of infections, supply and storage), the use of cell-free hemoglobin as an oxygen carrier substitute has been in the center of research interest for decades. Human hemoglobin has previously been synthesized in yeast, however the challenge is to balance the expression of the two different globin subunits, as well as the supply of the prosthetic heme required for obtaining the active hemoglobin (alpha(2)beta(2)). In this work we evaluated the expression of different combinations of alpha and beta peptides and combined this with metabolic engineering of the heme biosynthetic pathway. Through evaluation of several different strategies we showed that engineering the biosynthesis pathway can substantially increase the heme level in yeast cells, and this resulted in a significant enhancement of human hemoglobin production. Besides demonstration of improved hemoglobin production our work demonstrates a novel strategy for improving the production of complex proteins, especially multimers with a prosthetic group. Crown Copyright (C) 2013 Published by Elsevier Inc. on behalf of International Metabolic Engineering Society. All rights reserved.
  •  
42.
  • Liu, Zhengtao, et al. (författare)
  • Pyruvate kinase L/R is a regulator of lipid metabolism and mitochondrial function
  • 2019
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 52, s. 263-272
  • Tidskriftsartikel (refereegranskat)abstract
    • The pathogenesis of non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC) has been associated with altered expression of liver-specific genes including pyruvate kinase liver and red blood cell (PKLR), patatin-like phospholipase domain containing 3 (PNPLA3) and proprotein convertase subtilisin/kexin type 9 (PCSK9). Here, we inhibited and overexpressed the expression of these three genes in HepG2 cells, generated RNA-seq data before and after perturbation and revealed the altered global biological functions with the modulation of these genes using integrated network (IN) analysis. We found that modulation of these genes effects the total triglycerides levels within the cells and viability of the cells. Next, we generated IN for HepG2 cells, identified reporter transcription factors based on IN and found that the modulation of these genes affects key metabolic pathways associated with lipid metabolism (steroid biosynthesis, PPAR signalling pathway, fatty acid synthesis and oxidation) and cancer development (DNA replication, cell cycle and p53 signalling) involved in the progression of NAFLD and HCC. Finally, we observed that inhibition of PKLR lead to decreased glucose uptake and decreased mitochondrial activity in HepG2 cells. Hence, our systems level analysis indicated that PKLR can be targeted for development efficient treatment strategy for NAFLD and HCC.
  •  
43.
  • Luo, Hao, 1992, et al. (författare)
  • Modeling the metabolic dynamics at the genome-scale by optimized yield analysis
  • 2023
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 75, s. 119-130
  • Tidskriftsartikel (refereegranskat)abstract
    • The hybrid cybernetic model (HCM) approach is a dynamic modeling framework that integrates enzyme synthesis and activity regulation. It has been widely applied in bioreaction engineering, particularly in the simulation of microbial growth in different mixtures of carbon sources. In a HCM, the metabolic network is decomposed into elementary flux modes (EFMs), whereby the network can be reduced into a few pathways by yield analysis. However, applying the HCM approach on conventional genome-scale metabolic models (GEMs) is still a challenge due to the high computational demands. Here, we present a HCM strategy that introduced an optimized yield analysis algorithm (opt-yield-FBA) to simulate metabolic dynamics at the genome-scale without the need for EFMs calculation. The opt-yield-FBA is a flux-balance analysis (FBA) based method that can calculate optimal yield solutions and yield space for GEM. With the opt-yield-FBA algorithm, the HCM strategy can be applied to get the yield spaces and avoid the computational burden of EFMs, and it can therefore be applied for developing dynamic models for genome-scale metabolic networks. Here, we illustrate the strategy by applying the concept to simulate the dynamics of microbial communities.
  •  
44.
  • Ma, Tian, et al. (författare)
  • Lipid engineering combined with systematic metabolic engineering of Saccharomyces cerevisiae for high-yield production of lycopene
  • 2019
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 52, s. 134-142
  • Tidskriftsartikel (refereegranskat)abstract
    • Saccharomyces cerevisiae is an efficient host for natural-compound production and preferentially employed in academic studies and bioindustries. However, S. cerevisiae exhibits limited production capacity for lipophilic natural products, especially compounds that accumulate intracellularly, such as polyketides and carotenoids, with some engineered compounds displaying cytotoxicity. In this study, we used a nature-inspired strategy to establish an effective platform to improve lipid oil–triacylglycerol (TAG) metabolism and enable increased lycopene accumulation. Through systematic traditional engineering methods, we achieved relatively high-level production at 56.2 mg lycopene/g cell dry weight (cdw). To focus on TAG metabolism in order to increase lycopene accumulation, we overexpressed key genes associated with fatty acid synthesis and TAG production, followed by modulation of TAG fatty acyl composition by overexpressing a fatty acid desaturase (OLE1) and deletion of Seipin (FLD1), which regulates lipid-droplet size. Results showed that the engineered strain produced 70.5 mg lycopene/g cdw, a 25% increase relative to the original high-yield strain, with lycopene production reaching 2.37 g/L and 73.3 mg/g cdw in fed-batch fermentation and representing the highest lycopene yield in S. cerevisiae reported to date. These findings offer an effective strategy for extended systematic metabolic engineering through lipid engineering.
  •  
45.
  • Malm, Magdalena, 1983-, et al. (författare)
  • Harnessing secretory pathway differences between HEK293 and CHO to rescue production of difficult to express proteins
  • 2022
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 72, s. 171-187
  • Tidskriftsartikel (refereegranskat)abstract
    • Biologics represent the fastest growing group of therapeutics, but many advanced recombinant protein moieties remain difficult to produce. Here, we identify metabolic engineering targets limiting expression of recombinant human proteins through a systems biology analysis of the transcriptomes of CHO and HEK293 during recombinant expression. In an expression comparison of 24 difficult to express proteins, one third of the challenging human proteins displayed improved secretion upon host cell swapping from CHO to HEK293. Guided by a comprehensive transcriptomics comparison between cell lines, especially highlighting differences in secretory pathway utilization, a co-expression screening of 21 secretory pathway components validated ATF4, SRP9, JUN, PDIA3 and HSPA8 as productivity boosters in CHO. Moreover, more heavily glycosylated products benefitted more from the elevated activities of the N- and O-glycosyltransferases found in HEK293. Collectively, our results demonstrate the utilization of HEK293 for expression rescue of human proteins and suggest a methodology for identification of secretory pathway components for metabolic engineering of HEK293 and CHO.
  •  
46.
  • Mao, Jiwei, 1990, et al. (författare)
  • Fine-tuning of p-coumaric acid synthesis to increase (2S)-naringenin production in yeast
  • 2023
  • Ingår i: Metabolic Engineering. - 1096-7176 .- 1096-7184. ; 79, s. 192-202
  • Tidskriftsartikel (refereegranskat)abstract
    • (2S)-Naringenin is a key precursor for biosynthesis of various high-value flavonoids and possesses a variety of nutritional and pharmaceutical properties on human health. Systematic optimization approaches have been employed to improve (2S)-naringenin production in different microbial hosts. However, very few studies have focused on the spatiotemporal distribution of (2S)-naringenin and the related pathway intermediate p-coumaric acid, which is an important factor for efficient production. Here, we first optimized the (2S)-naringenin biosynthetic pathway by alleviating the bottleneck downstream of p-coumaric acid and increasing malonyl-CoA supply, which improved (2S)-naringenin production but significant accumulation of p-coumaric acid still existed extracellularly. We thus established a dual dynamic control system through combining a malonyl-CoA biosensor regulator and an RNAi strategy, to autonomously control the synthesis of p-coumaric acid with the supply of malonyl-CoA. Furthermore, screening potential transporters led to identification of Pdr12 for improved (2S)-naringenin production and reduced accumulation of p-coumaric acid. Finally, a titer of 2.05 g/L (2S)-naringenin with negligible accumulation of p-coumaric acid was achieved in a fed batch fermentation. Our work highlights the importance of systematic control of pathway intermediates for efficient microbial production of plant natural products.
  •  
47.
  • Mapelli, Valeria, 1978, et al. (författare)
  • Metabolic and Bioprocess Engineering for Production of selenized yeast with increased content of seleno-methylselenocysteine
  • 2011
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 13:3, s. 282-293
  • Tidskriftsartikel (refereegranskat)abstract
    • Specific Se-metabolites have been recognized as main responsible for beneficial effects of Se-enriched diet and Se-methylselenocysteine (SeMCys) is thought to be among the most effective ones. Here we show that an engineered Saccharomyces cerevisiae strain expressing a codon optimized heterologous selenocysteine-methyltransferase and endowed with high intracellular levels of S-adenosyl-methionine was able to accumulate SeMCys at levels higher than commercial selenized yeasts. A fine tuned carbon- and sulphate-limited fed-batch bioprocess was crucial to achieve good yields of biomass and SeMCys. Through the coupling of metabolic and bioprocess engineering we achieved a ~24-fold increase in SeMCys, compared to certified reference material of selenized yeast. In addition, we investigated the interplay between sulphur and selenium metabolism and the possibility that redox imbalance occurred along with intracellular accumulation of Se. Collectively, our data show how the combination of metabolic and bioprocess engineering can be used for the production of selenized yeast enriched with beneficial Se-metabolites.
  •  
48.
  • Marques, W. L., et al. (författare)
  • Combined engineering of disaccharide transport and phosphorolysis for enhanced ATP yield from sucrose fermentation in Saccharomyces cerevisiae
  • 2018
  • Ingår i: Metabolic engineering. - : Academic Press Inc.. - 1096-7176 .- 1096-7184. ; 45, s. 121-133
  • Tidskriftsartikel (refereegranskat)abstract
    • Anaerobic industrial fermentation processes do not require aeration and intensive mixing and the accompanying cost savings are beneficial for production of chemicals and fuels. However, the free-energy conservation of fermentative pathways is often insufficient for the production and export of the desired compounds and/or for cellular growth and maintenance. To increase free-energy conservation during fermentation of the industrially relevant disaccharide sucrose by Saccharomyces cerevisiae, we first replaced the native yeast α-glucosidases by an intracellular sucrose phosphorylase from Leuconostoc mesenteroides (LmSPase). Subsequently, we replaced the native proton-coupled sucrose uptake system by a putative sucrose facilitator from Phaseolus vulgaris (PvSUF1). The resulting strains grew anaerobically on sucrose at specific growth rates of 0.09 ± 0.02 h−1 (LmSPase) and 0.06 ± 0.01 h−1 (PvSUF1, LmSPase). Overexpression of the yeast PGM2 gene, which encodes phosphoglucomutase, increased anaerobic growth rates on sucrose of these strains to 0.23 ± 0.01 h−1 and 0.08 ± 0.00 h−1, respectively. Determination of the biomass yield in anaerobic sucrose-limited chemostat cultures was used to assess the free-energy conservation of the engineered strains. Replacement of intracellular hydrolase with a phosphorylase increased the biomass yield on sucrose by 31%. Additional replacement of the native proton-coupled sucrose uptake system by PvSUF1 increased the anaerobic biomass yield by a further 8%, resulting in an overall increase of 41%. By experimentally demonstrating an energetic benefit of the combined engineering of disaccharide uptake and cleavage, this study represents a first step towards anaerobic production of compounds whose metabolic pathways currently do not conserve sufficient free-energy.
  •  
49.
  • Meijer, S, et al. (författare)
  • Overexpression of isocitrate lyase-glyoxylate bypass influence on matabolism in Aspergillus niger
  • 2009
  • Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; :11, s. 107-116
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to improve the production of succinate and malate by the filamentous fungus Aspergillus niger the activity of the glyoxylate bypass pathway was increased by over-expression of the isocitrate lyase (icl) gene. The hypothesis was that when isocitrate lyase was up-regulated the flux towards glyoxylate would increase, leading to excess formation of malate and succinate compared to the wild-type. However, metabolic network analysis showed that an increased icl expression did not result in an increased glyoxylate bypass flux. The analysis did show a global response with respect to gene expression, leading to an increased flux through the oxidative part of the TCA cycle. Instead of an increased production of succinate and malate, a major increase in fumarate production was observed. The effect of malonate, a competative inhibitor of succinate dehydrogenase (SDH), on the physiological behaviour of the cells was investigated. Inhibition of SDH was expected to lead to succinate production, but this was not observed. There was an increase in citrate and oxalate production in the wild-type strain. Furthermore, in the strain with over-expression of icl the organic acid production shifted from fumarate towards malate production when malonate was added to the cultivation medium. Overall, the icl over-expression and malonate addition had a significant impact on metabolism and on organic acid production profiles. Although the expected succiante and malate formation was not observed, a distinct and interesting production of fumarate and malate was found.
  •  
50.
  • Miao, Rui, et al. (författare)
  • Protein engineering of α-ketoisovalerate decarboxylase for improved isobutanol production in Synechocystis PCC 6803
  • 2018
  • Ingår i: Metabolic engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 47, s. 42-48
  • Tidskriftsartikel (refereegranskat)abstract
    • Protein engineering is a powerful tool to modify e.g. protein stability, activity and substrate selectivity. Heterologous expression of the enzyme α-ketoisovalerate decarboxylase (Kivd) in the unicellular cyanobacterium Synechocystis PCC 6803 results in cells producing isobutanol and 3-methyl-1-butanol, with Kivd identified as a potential bottleneck. In the present study, we used protein engineering of Kivd to improve isobutanol production in Synechocystis PCC 6803. Isobutanol is a flammable compound that can be used as a biofuel due to its high energy density and suitable physical and chemical properties. Single replacement, either Val461 to isoleucine or Ser286 to threonine, increased the Kivd activity significantly, both in vivo and in vitro resulting in increased overall production while isobutanol production was increased more than 3-methyl-1-butanol production. Moreover, among all the engineered strains examined, the strain with the combined modification V461I/S286T showed the highest (2.4 times) improvement of isobutanol-to-3M1B molar ratio, which was due to a decrease of the activity towards 3M1B production. Protein engineering of Kivd resulted in both enhanced total catalytic activity and preferential shift towards isobutanol production in Synechocystis PCC 6803.
  •  
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