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Chen Y, Nielsen J. Biobased organic acids production by metabolically engineered microorganisms. Curr Opin Biotechnol 2015; 37:165-172. [PMID: 26748037 DOI: 10.1016/j.copbio.2015.11.004] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Revised: 10/26/2015] [Accepted: 11/03/2015] [Indexed: 12/30/2022]
Abstract
Bio-based production of organic acids via microbial fermentation has been traditionally used in food industry. With the recent desire to develop more sustainable bioprocesses for production of fuels, chemicals and materials, the market for microbial production of organic acids has been further expanded as organic acids constitute a key group among top building block chemicals that can be produced from renewable resources. Here we review the current status for production of citric acid and lactic acid, and we highlight the use of modern metabolic engineering technologies to develop high performance microbes for production of succinic acid and 3-hydroxypropionic acid. Also, the key limitations and challenges in microbial organic acids production are discussed.
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Affiliation(s)
- Yun Chen
- Department of Biology & Biological Engineering, Chalmers University of Technology, SE412 96 Gothenburg, Sweden; Novo Nordisk Foundation Center for Biosustainability, Chalmers University of Technology, SE412 96 Gothenburg, Sweden
| | - Jens Nielsen
- Department of Biology & Biological Engineering, Chalmers University of Technology, SE412 96 Gothenburg, Sweden; Novo Nordisk Foundation Center for Biosustainability, Chalmers University of Technology, SE412 96 Gothenburg, Sweden; Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, DK2970 Hørsholm, Denmark.
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52
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13C-Metabolic Flux Analysis: An Accurate Approach to Demystify Microbial Metabolism for Biochemical Production. Bioengineering (Basel) 2015; 3:bioengineering3010003. [PMID: 28952565 PMCID: PMC5597161 DOI: 10.3390/bioengineering3010003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 12/10/2015] [Accepted: 12/18/2015] [Indexed: 12/15/2022] Open
Abstract
Metabolic engineering of various industrial microorganisms to produce chemicals, fuels, and drugs has raised interest since it is environmentally friendly, sustainable, and independent of nonrenewable resources. However, microbial metabolism is so complex that only a few metabolic engineering efforts have been able to achieve a satisfactory yield, titer or productivity of the target chemicals for industrial commercialization. In order to overcome this challenge, 13C Metabolic Flux Analysis (13C-MFA) has been continuously developed and widely applied to rigorously investigate cell metabolism and quantify the carbon flux distribution in central metabolic pathways. In the past decade, many 13C-MFA studies have been performed in academic labs and biotechnology industries to pinpoint key issues related to microbe-based chemical production. Insightful information about the metabolic rewiring has been provided to guide the development of the appropriate metabolic engineering strategies for improving the biochemical production. In this review, we will introduce the basics of 13C-MFA and illustrate how 13C-MFA has been applied via integration with metabolic engineering to identify and tackle the rate-limiting steps in biochemical production for various host microorganisms
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53
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Top value platform chemicals: bio-based production of organic acids. Curr Opin Biotechnol 2015; 36:168-75. [DOI: 10.1016/j.copbio.2015.08.022] [Citation(s) in RCA: 193] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 08/11/2015] [Accepted: 08/18/2015] [Indexed: 11/19/2022]
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54
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McAtee AG, Jazmin LJ, Young JD. Application of isotope labeling experiments and 13C flux analysis to enable rational pathway engineering. Curr Opin Biotechnol 2015; 36:50-6. [DOI: 10.1016/j.copbio.2015.08.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 08/06/2015] [Accepted: 08/09/2015] [Indexed: 12/24/2022]
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55
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Systems strategies for developing industrial microbial strains. Nat Biotechnol 2015; 33:1061-72. [DOI: 10.1038/nbt.3365] [Citation(s) in RCA: 357] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Accepted: 08/23/2015] [Indexed: 12/11/2022]
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56
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Ruckerbauer DE, Jungreuthmayer C, Zanghellini J. Predicting genetic engineering targets with Elementary Flux Mode Analysis: a review of four current methods. N Biotechnol 2015; 32:534-46. [PMID: 25917465 DOI: 10.1016/j.nbt.2015.03.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 03/21/2015] [Accepted: 03/30/2015] [Indexed: 01/14/2023]
Abstract
Elementary flux modes (EFMs) are a well-established tool in metabolic modeling. EFMs are minimal, feasible, steady state pathways through a metabolic network. They are used in various approaches to predict targets for genetic interventions in order to increase production of a molecule of interest via a host cell. Here we give an introduction to the concept of EFMs, present an overview of four methods which use EFMs in order to predict engineering targets and lastly use a toy model and a small-scale metabolic model to demonstrate and compare the capabilities of these methods.
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Affiliation(s)
- David E Ruckerbauer
- Austrian Centre of Industrial Biotechnology, Muthgasse 11, A1190 Vienna, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Christian Jungreuthmayer
- Austrian Centre of Industrial Biotechnology, Muthgasse 11, A1190 Vienna, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Jürgen Zanghellini
- Austrian Centre of Industrial Biotechnology, Muthgasse 11, A1190 Vienna, Austria; Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria.
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57
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Becker J, Wittmann C. Advanced Biotechnology: Metabolically Engineered Cells for the Bio-Based Production of Chemicals and Fuels, Materials, and Health-Care Products. Angew Chem Int Ed Engl 2015; 54:3328-50. [DOI: 10.1002/anie.201409033] [Citation(s) in RCA: 223] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Indexed: 12/16/2022]
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58
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Biotechnologie von Morgen: metabolisch optimierte Zellen für die bio-basierte Produktion von Chemikalien und Treibstoffen, Materialien und Gesundheitsprodukten. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201409033] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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59
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Large-Scale 13C flux profiling reveals conservation of the Entner-Doudoroff pathway as a glycolytic strategy among marine bacteria that use glucose. Appl Environ Microbiol 2015; 81:2408-22. [PMID: 25616803 DOI: 10.1128/aem.03157-14] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Marine bacteria form one of the largest living surfaces on Earth, and their metabolic activity is of fundamental importance for global nutrient cycling. Here, we explored the largely unknown intracellular pathways in 25 microbes representing different classes of marine bacteria that use glucose: Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia of the Bacteriodetes phylum. We used (13)C isotope experiments to infer metabolic fluxes through their carbon core pathways. Notably, 90% of all strains studied use the Entner-Doudoroff (ED) pathway for glucose catabolism, whereas only 10% rely on the Embden-Meyerhof-Parnas (EMP) pathway. This result differed dramatically from the terrestrial model strains studied, which preferentially used the EMP pathway yielding high levels of ATP. Strains using the ED pathway exhibited a more robust resistance against the oxidative stress typically found in this environment. An important feature contributing to the preferential use of the ED pathway in the oceans could therefore be enhanced supply of NADPH through this pathway. The marine bacteria studied did not specifically rely on a distinct anaplerotic route, but the carboxylation of phosphoenolpyruvate (PEP) or pyruvate for fueling of the tricarboxylic acid (TCA) cycle was evenly distributed. The marine isolates studied belong to clades that dominate the uptake of glucose, a major carbon source for bacteria in seawater. Therefore, the ED pathway may play a significant role in the cycling of mono- and polysaccharides by bacterial communities in marine ecosystems.
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60
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Choi S, Song CW, Shin JH, Lee SY. Biorefineries for the production of top building block chemicals and their derivatives. Metab Eng 2015; 28:223-239. [PMID: 25576747 DOI: 10.1016/j.ymben.2014.12.007] [Citation(s) in RCA: 252] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Revised: 12/27/2014] [Accepted: 12/29/2014] [Indexed: 01/11/2023]
Abstract
Due to the growing concerns on the climate change and sustainability on petrochemical resources, DOE selected and announced the bio-based top 12 building blocks and discussed the needs for developing biorefinery technologies to replace the current petroleum based industry in 2004. Over the last 10 years after its announcement, many studies have been performed for the development of efficient technologies for the bio-based production of these chemicals and derivatives. Now, ten chemicals among these top 12 chemicals, excluding the l-aspartic acid and 3-hydroxybutyrolactone, have already been commercialized or are close to commercialization. In this paper, we review the current status of biorefinery development for the production of these platform chemicals and their derivatives. In addition, current technological advances on industrial strain development for the production of platform chemicals using micro-organisms will be covered in detail with case studies on succinic acid and 3-hydroxypropionic acid as examples.
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Affiliation(s)
- Sol Choi
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus program), Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea; BioProcess Engineering Research Center, KAIST, Daejeon 305-701, Republic of Korea
| | - Chan Woo Song
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus program), Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
| | - Jae Ho Shin
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus program), Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea
| | - Sang Yup Lee
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus program), Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea; BioProcess Engineering Research Center, KAIST, Daejeon 305-701, Republic of Korea; BioInformatics Research Center, KAIST, Daejeon 305-701, Republic of Korea; The Novo Nordisk Foundation Center for Biosustainability, Technical University Denmark, Hørsholm, Denmark.
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61
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Li Q, Xing J. Microbial Succinic Acid Production Using Different Bacteria Species. MICROORGANISMS IN BIOREFINERIES 2015. [DOI: 10.1007/978-3-662-45209-7_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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62
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Jansen MLA, van Gulik WM. Towards large scale fermentative production of succinic acid. Curr Opin Biotechnol 2014; 30:190-7. [DOI: 10.1016/j.copbio.2014.07.003] [Citation(s) in RCA: 151] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 06/18/2014] [Accepted: 07/21/2014] [Indexed: 01/04/2023]
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63
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Bücker R, Heroven AK, Becker J, Dersch P, Wittmann C. The pyruvate-tricarboxylic acid cycle node: a focal point of virulence control in the enteric pathogen Yersinia pseudotuberculosis. J Biol Chem 2014; 289:30114-32. [PMID: 25164818 DOI: 10.1074/jbc.m114.581348] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Despite our increasing knowledge of the specific pathogenicity factors in bacteria, the contribution of metabolic processes to virulence is largely unknown. Here, we elucidate a tight connection between pathogenicity and core metabolism in the enteric pathogen Yersinia pseudotuberculosis by integrated transcriptome and [(13)C]fluxome analysis of the wild type and virulence-regulator mutants. During aerobic growth on glucose, Y. pseudotuberculosis reveals an unusual flux distribution with a high level of secreted pyruvate. The absence of the transcriptional and post-transcriptional regulators RovA, CsrA, and Crp strongly perturbs the fluxes of carbon core metabolism at the level of pyruvate metabolism and the tricarboxylic acid (TCA) cycle, and these perturbations are accompanied by transcriptional changes in the corresponding enzymes. Knock-outs of regulators of this metabolic branch point and of its central enzyme, pyruvate kinase (ΔpykF), result in mutants with significantly reduced virulence in an oral mouse infection model. In summary, our work identifies the pyruvate-TCA cycle node as a focal point for controlling the host colonization and virulence of Yersinia.
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Affiliation(s)
- René Bücker
- From the Institute of Systems Biotechnology, Saarland University, 66123 Saarbrücken, the Institute of Biochemical Engineering, Technische Universität, Braunschweig and
| | - Ann Kathrin Heroven
- the Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Judith Becker
- From the Institute of Systems Biotechnology, Saarland University, 66123 Saarbrücken
| | - Petra Dersch
- the Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Christoph Wittmann
- From the Institute of Systems Biotechnology, Saarland University, 66123 Saarbrücken,
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64
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Jeong BY, Wittmann C, Kato T, Park EY. Comparative metabolic flux analysis of an Ashbya gossypii wild type strain and a high riboflavin-producing mutant strain. J Biosci Bioeng 2014; 119:101-6. [PMID: 25128926 DOI: 10.1016/j.jbiosc.2014.06.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 06/18/2014] [Accepted: 06/19/2014] [Indexed: 11/18/2022]
Abstract
In the present study, we analyzed the central metabolic pathway of an Ashbya gossypii wild type strain and a riboflavin over-producing mutant strain developed in a previous study in order to characterize the riboflavin over-production pathway. (13)C-Metabolic flux analysis ((13)C-MFA) was carried out in both strains, and the resulting data were fit to a steady-state flux isotopomer model using OpenFLUX. Flux to pentose-5-phosphate (P5P) via the pentose phosphate pathway (PPP) was 9% higher in the mutant strain compared to the wild type strain. The flux from purine synthesis to riboflavin in the mutant strain was 1.6%, while that of the wild type strain was only 0.1%, a 16-fold difference. In addition, the flux from the cytoplasmic pyruvate pool to the extracellular metabolites, pyruvate, lactate, and alanine, was 2-fold higher in the mutant strain compared to the wild type strain. This result demonstrates that increased guanosine triphosphate (GTP) flux through the PPP and purine synthesis pathway (PSP) increased riboflavin production in the mutant strain. The present study provides the first insight into metabolic flux through the central carbon pathway in A. gossypii and sets the foundation for development of a quantitative and functional model of the A. gossypii metabolic network.
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Affiliation(s)
- Bo-Young Jeong
- Laboratory of Biotechnology, Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan.
| | - Christoph Wittmann
- Institute of Biochemical Engineering, Braunschweig University of Technology, Gauss Street 17, Braunschweig 38106, Germany.
| | - Tatsuya Kato
- Research Institute of Green Science and Technology, Shizuoka University, 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan.
| | - Enoch Y Park
- Laboratory of Biotechnology, Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan; Research Institute of Green Science and Technology, Shizuoka University, 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan.
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65
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Hollinshead W, He L, Tang YJ. Biofuel production: an odyssey from metabolic engineering to fermentation scale-up. Front Microbiol 2014; 5:344. [PMID: 25071754 PMCID: PMC4088188 DOI: 10.3389/fmicb.2014.00344] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 06/20/2014] [Indexed: 12/21/2022] Open
Abstract
Metabolic engineering has developed microbial cell factories that can convert renewable carbon sources into biofuels. Current molecular biology tools can efficiently alter enzyme levels to redirect carbon fluxes toward biofuel production, but low product yield and titer in large bioreactors prevent the fulfillment of cheap biofuels. There are three major roadblocks preventing economical biofuel production. First, carbon fluxes from the substrate dissipate into a complex metabolic network. Besides the desired product, microbial hosts direct carbon flux to synthesize biomass, overflow metabolites, and heterologous enzymes. Second, microbial hosts need to oxidize a large portion of the substrate to generate both ATP and NAD(P)H to power biofuel synthesis. High cell maintenance, triggered by the metabolic burdens from genetic modifications, can significantly affect the ATP supply. Thereby, fermentation of advanced biofuels (such as biodiesel and hydrocarbons) often requires aerobic respiration to resolve the ATP shortage. Third, mass transfer limitations in large bioreactors create heterogeneous growth conditions and micro-environmental fluctuations (such as suboptimal O2 level and pH) that induce metabolic stresses and genetic instability. To overcome these limitations, fermentation engineering should merge with systems metabolic engineering. Modern fermentation engineers need to adopt new metabolic flux analysis tools that integrate kinetics, hydrodynamics, and 13C-proteomics, to reveal the dynamic physiologies of the microbial host under large bioreactor conditions. Based on metabolic analyses, fermentation engineers may employ rational pathway modifications, synthetic biology circuits, and bioreactor control algorithms to optimize large-scale biofuel production.
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Affiliation(s)
- Whitney Hollinshead
- Department of Energy, Environmental and Chemical Engineering, Washington University St. Louis, MO, USA
| | - Lian He
- Department of Energy, Environmental and Chemical Engineering, Washington University St. Louis, MO, USA
| | - Yinjie J Tang
- Department of Energy, Environmental and Chemical Engineering, Washington University St. Louis, MO, USA
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66
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Elucidation of intrinsic biosynthesis yields using 13C-based metabolism analysis. Microb Cell Fact 2014; 13:42. [PMID: 24642094 PMCID: PMC3994946 DOI: 10.1186/1475-2859-13-42] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 03/12/2014] [Indexed: 11/10/2022] Open
Abstract
This paper discusses the use of 13C-based metabolism analysis for the assessment of intrinsic product yields - the actual carbon contribution from a single carbon substrate to the final product via a specific biosynthesis route - in the following four cases. First, undefined nutrients (such as yeast extract) in fermentation may contribute significantly to product synthesis, which can be quantified through an isotopic dilution method. Second, product and biomass synthesis may be dependent on the co-metabolism of multiple-carbon sources. 13C labeling experiments can track the fate of each carbon substrate in the cell metabolism and identify which substrate plays a main role in product synthesis. Third, 13C labeling can validate and quantify the contribution of the engineered pathway (versus the native pathway) to the product synthesis. Fourth, the loss of catabolic energy due to cell maintenance (energy used for functions other than production of new cell components) and low P/O ratio (Phosphate/Oxygen Ratio) significantly reduces product yields. Therefore, 13C-metabolic flux analysis is needed to assess the influence of suboptimal energy metabolism on microbial productivity, and determine how ATP/NAD(P)H are partitioned among various cellular functions. Since product yield is a major determining factor in the commercialization of a microbial cell factory, we foresee that 13C-isotopic labeling experiments, even without performing extensive flux calculations, can play a valuable role in the development and verification of microbial cell factories.
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67
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Carbon flux analysis by 13C nuclear magnetic resonance to determine the effect of CO2 on anaerobic succinate production by Corynebacterium glutamicum. Appl Environ Microbiol 2014; 80:3015-24. [PMID: 24610842 DOI: 10.1128/aem.04189-13] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Wild-type Corynebacterium glutamicum produces a mixture of lactic, succinic, and acetic acids from glucose under oxygen deprivation. We investigated the effect of CO2 on the production of organic acids in a two-stage process: cells were grown aerobically in glucose, and subsequently, organic acid production by nongrowing cells was studied under anaerobic conditions. The presence of CO2 caused up to a 3-fold increase in the succinate yield (1 mol per mol of glucose) and about 2-fold increase in acetate, both at the expense of l-lactate production; moreover, dihydroxyacetone formation was abolished. The redistribution of carbon fluxes in response to CO2 was estimated by using (13)C-labeled glucose and (13)C nuclear magnetic resonance (NMR) analysis of the labeling patterns in end products. The flux analysis showed that 97% of succinate was produced via the reductive part of the tricarboxylic acid cycle, with the low activity of the oxidative branch being sufficient to provide the reducing equivalents needed for the redox balance. The flux via the pentose phosphate pathway was low (~5%) regardless of the presence or absence of CO2. Moreover, there was significant channeling of carbon to storage compounds (glycogen and trehalose) and concomitant catabolism of these reserves. The intracellular and extracellular pools of lactate and succinate were measured by in vivo NMR, and the stoichiometry (H(+):organic acid) of the respective exporters was calculated. This study shows that it is feasible to take advantage of natural cellular regulation mechanisms to obtain high yields of succinate with C. glutamicum without genetic manipulation.
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68
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Physiological characterization of the high malic acid-producing Aspergillus oryzae strain 2103a-68. Appl Microbiol Biotechnol 2014; 98:3517-27. [DOI: 10.1007/s00253-013-5465-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 12/09/2013] [Accepted: 12/10/2013] [Indexed: 01/11/2023]
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