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Nawab S, Zhang Y, Ullah MW, Lodhi AF, Shah SB, Rahman MU, Yong YC. Microbial host engineering for sustainable isobutanol production from renewable resources. Appl Microbiol Biotechnol 2024; 108:33. [PMID: 38175234 DOI: 10.1007/s00253-023-12821-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Revised: 12/10/2023] [Accepted: 12/18/2023] [Indexed: 01/05/2024]
Abstract
Due to the limited resources and environmental problems associated with fossil fuels, there is a growing interest in utilizing renewable resources for the production of biofuels through microbial fermentation. Isobutanol is a promising biofuel that could potentially replace gasoline. However, its production efficiency is currently limited by the use of naturally isolated microorganisms. These naturally isolated microorganisms often encounter problems such as a limited range of substrates, low tolerance to solvents or inhibitors, feedback inhibition, and an imbalanced redox state. This makes it difficult to improve their production efficiency through traditional process optimization methods. Fortunately, recent advancements in genetic engineering technologies have made it possible to enhance microbial hosts for the increased production of isobutanol from renewable resources. This review provides a summary of the strategies and synthetic biology approaches that have been employed in the past few years to improve naturally isolated or non-natural microbial hosts for the enhanced production of isobutanol by utilizing different renewable resources. Furthermore, it also discusses the challenges that are faced by engineered microbial hosts and presents future perspectives to enhancing isobutanol production. KEY POINTS: • Promising potential of isobutanol to replace gasoline • Engineering of native and non-native microbial host for isobutanol production • Challenges and opportunities for enhanced isobutanol production.
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Affiliation(s)
- Said Nawab
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - YaFei Zhang
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Muhammad Wajid Ullah
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Adil Farooq Lodhi
- Department of Microbiology, Faculty of Biological and Health Sciences, Hazara University, Mansehra, Pakistan
| | - Syed Bilal Shah
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Mujeeb Ur Rahman
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Yang-Chun Yong
- Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013, China.
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Moreira JPC, Heap JT, Alves JI, Domingues L. Developing a genetic engineering method for Acetobacterium wieringae to expand one-carbon valorization pathways. BIOTECHNOLOGY FOR BIOFUELS AND BIOPRODUCTS 2023; 16:24. [PMID: 36788587 PMCID: PMC9930230 DOI: 10.1186/s13068-023-02259-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 01/05/2023] [Indexed: 02/16/2023]
Abstract
BACKGROUND Developing new bioprocesses to produce chemicals and fuels with reduced production costs will greatly facilitate the replacement of fossil-based raw materials. In most fermentation bioprocesses, the feedstock usually represents the highest cost, which becomes the target for cost reduction. Additionally, the biorefinery concept advocates revenue growth from the production of several compounds using the same feedstock. Taken together, the production of bio commodities from low-cost gas streams containing CO, CO2, and H2, obtained from the gasification of any carbon-containing waste streams or off-gases from heavy industry (steel mills, processing plants, or refineries), embodies an opportunity for affordable and renewable chemical production. To achieve this, by studying non-model autotrophic acetogens, current limitations concerning low growth rates, toxicity by gas streams, and low productivity may be overcome. The Acetobacterium wieringae strain JM is a novel autotrophic acetogen that is capable of producing acetate and ethanol. It exhibits faster growth rates on various gaseous compounds, including carbon monoxide, compared to other Acetobacterium species, making it potentially useful for industrial applications. The species A. wieringae has not been genetically modified, therefore developing a genetic engineering method is important for expanding its product portfolio from gas fermentation and overall improving the characteristics of this acetogen for industrial demands. RESULTS This work reports the development and optimization of an electrotransformation protocol for A. wieringae strain JM, which can also be used in A. wieringae DSM 1911, and A. woodii DSM 1030. We also show the functionality of the thiamphenicol resistance marker, catP, and the functionality of the origins of replication pBP1, pCB102, pCD6, and pIM13 in all tested Acetobacterium strains, with transformation efficiencies of up to 2.0 × 103 CFU/μgDNA. Key factors affecting electrotransformation efficiency include OD600 of cell harvesting, pH of resuspension buffer, the field strength of the electric pulse, and plasmid amount. Using this method, the acetone production operon from Clostridium acetobutylicum was efficiently introduced in all tested Acetobacterium spp., leading to non-native biochemical acetone production via plasmid-based expression. CONCLUSIONS A. wieringae can be electrotransformed at high efficiency using different plasmids with different replication origins. The electrotransformation procedure and tools reported here unlock the genetic and metabolic manipulation of the biotechnologically relevant A. wieringae strains. For the first time, non-native acetone production is shown in A. wieringae.
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Affiliation(s)
- João P. C. Moreira
- grid.10328.380000 0001 2159 175XCEB - Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal ,LABBELS - Associate Laboratory, Braga/Guimarães, Portugal
| | - John T. Heap
- grid.4563.40000 0004 1936 8868School of Life Sciences, University of Nottingham, Biodiscovery Institute, University Park, Nottingham, NG7 2RD UK
| | - Joana I. Alves
- grid.10328.380000 0001 2159 175XCEB - Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal ,LABBELS - Associate Laboratory, Braga/Guimarães, Portugal
| | - Lucília Domingues
- CEB - Centre of Biological Engineering, University of Minho, 4710-057, Braga, Portugal. .,LABBELS - Associate Laboratory, Braga/Guimarães, Portugal.
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Zeldes B, Poehlein A, Jain S, Baum C, Daniel R, Müller V, Basen M. DNA uptake from a laboratory environment drives unexpected adaptation of a thermophile to a minor medium component. ISME COMMUNICATIONS 2023; 3:2. [PMID: 37938748 PMCID: PMC9834392 DOI: 10.1038/s43705-022-00211-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Revised: 12/19/2022] [Accepted: 12/22/2022] [Indexed: 06/01/2023]
Abstract
DNA uptake is widespread among microorganisms and considered a strategy for rapid adaptation to new conditions. While both DNA uptake and adaptation are referred to in the context of natural environments, they are often studied in laboratories under defined conditions. For example, a strain of the thermophile Thermoanaerobacter kivui had been adapted to growth on high concentrations of carbon monoxide (CO). Unusual phenotypes of the CO-adapted strain prompted us to examine it more closely, revealing a horizontal gene transfer (HGT) event from another thermophile, Thermoanaerobacter sp. strain X514, being cultured in the same laboratory. The transferred genes conferred on T. kivui the ability to utilize trehalose, a trace component of the yeast-extract added to the media during CO-adaptation. This same HGT event simultaneously deleted a native operon for thiamine biosynthesis, which likely explains why the CO-adapted strain grows poorly without added vitamins. Attempts to replicate this HGT by providing T. kivui with genomic DNA from Thermoanaerobacter sp. strain X514 revealed that it is easily reproducible in the lab. This subtle form of "genome contamination" is difficult to detect, since the genome remains predominantly T. kivui, and no living cells from the original contamination remain. Unexpected HGT between two microorganisms as well as simultaneous adaptation to several conditions may occur often and unrecognized in laboratory environments, requiring caution and careful monitoring of phenotype and genotype of microorganisms that are naturally-competent for DNA uptake.
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Affiliation(s)
- Benjamin Zeldes
- Microbiology, Institute of Biological Sciences, University of Rostock, Rostock, Germany
| | - Anja Poehlein
- Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Georg-August University, Göttingen, Germany
| | - Surbhi Jain
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe University, Frankfurt/Main, Germany
| | - Christoph Baum
- Microbiology, Institute of Biological Sciences, University of Rostock, Rostock, Germany
| | - Rolf Daniel
- Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Georg-August University, Göttingen, Germany
| | - Volker Müller
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Goethe University, Frankfurt/Main, Germany
| | - Mirko Basen
- Microbiology, Institute of Biological Sciences, University of Rostock, Rostock, Germany.
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Ricci L, Seifert A, Bernacchi S, Fino D, Pirri CF, Re A. Leveraging substrate flexibility and product selectivity of acetogens in two-stage systems for chemical production. Microb Biotechnol 2022; 16:218-237. [PMID: 36464980 PMCID: PMC9871533 DOI: 10.1111/1751-7915.14172] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 10/31/2022] [Accepted: 11/08/2022] [Indexed: 12/09/2022] Open
Abstract
Carbon dioxide (CO2 ) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H2 -dependent CO2 gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state-of-the-art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double-stage biotechnological production processes that use CO2 as sole carbon feedstock and H2 as energy carrier for products' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products' spectrum. Alternatively, when the first stage is abiotic, the integrated two-stage scheme foresees, in the first stage, the catalytic transformation of CO2 into C1 products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO2 abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production.
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Affiliation(s)
- Luca Ricci
- Department of Applied Science and TechnologyPolitecnico di TorinoTurinItaly,Centre for Sustainable Future TechnologiesFondazione Istituto Italiano di TecnologiaTurinItaly
| | | | | | - Debora Fino
- Department of Applied Science and TechnologyPolitecnico di TorinoTurinItaly,Centre for Sustainable Future TechnologiesFondazione Istituto Italiano di TecnologiaTurinItaly
| | - Candido Fabrizio Pirri
- Department of Applied Science and TechnologyPolitecnico di TorinoTurinItaly,Centre for Sustainable Future TechnologiesFondazione Istituto Italiano di TecnologiaTurinItaly
| | - Angela Re
- Department of Applied Science and TechnologyPolitecnico di TorinoTurinItaly,Centre for Sustainable Future TechnologiesFondazione Istituto Italiano di TecnologiaTurinItaly
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Dykstra JC, van Oort J, Yazdi AT, Vossen E, Patinios C, van der Oost J, Sousa DZ, Kengen SWM. Metabolic engineering of Clostridium autoethanogenum for ethyl acetate production from CO. Microb Cell Fact 2022; 21:243. [DOI: 10.1186/s12934-022-01964-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Accepted: 10/18/2022] [Indexed: 11/25/2022] Open
Abstract
Abstract
Background
Ethyl acetate is a bulk chemical traditionally produced via energy intensive chemical esterification. Microbial production of this compound offers promise as a more sustainable alternative process. So far, efforts have focused on using sugar-based feedstocks for microbial ester production, but extension to one-carbon substrates, such as CO and CO2/H2, is desirable. Acetogens present a promising microbial platform for the production of ethyl esters from these one-carbon substrates.
Results
We engineered the acetogen C. autoethanogenum to produce ethyl acetate from CO by heterologous expression of an alcohol acetyltransferase (AAT), which catalyzes the formation of ethyl acetate from acetyl-CoA and ethanol. Two AATs, Eat1 from Kluyveromyces marxianus and Atf1 from Saccharomyces cerevisiae, were expressed in C. autoethanogenum. Strains expressing Atf1 produced up to 0.2 mM ethyl acetate. Ethyl acetate production was barely detectable (< 0.01 mM) for strains expressing Eat1. Supplementation of ethanol was investigated as potential boost for ethyl acetate production but resulted only in a 1.5-fold increase (0.3 mM ethyl acetate). Besides ethyl acetate, C. autoethanogenum expressing Atf1 could produce 4.5 mM of butyl acetate when 20 mM butanol was supplemented to the growth medium.
Conclusions
This work offers for the first time a proof-of-principle that autotrophic short chain ester production from C1-carbon feedstocks is possible and offers leads on how this approach can be optimized in the future.
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Baur T, Wentzel A, Dürre P. Production of propionate using metabolically engineered strains of Clostridium saccharoperbutylacetonicum. Appl Microbiol Biotechnol 2022; 106:7547-7562. [PMID: 36282302 PMCID: PMC9666320 DOI: 10.1007/s00253-022-12210-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 09/22/2022] [Accepted: 09/23/2022] [Indexed: 12/04/2022]
Abstract
Abstract The carboxylic acid propionate is a valuable platform chemical with applications in various fields. The biological production of this acid has become of great interest as it can be considered a sustainable alternative to petrochemical synthesis. In this work, Clostridium saccharoperbutylacetonicum was metabolically engineered to produce propionate via the acrylate pathway. In total, the established synthetic pathway comprised eight genes encoding the enzymes catalyzing the conversion of pyruvate to propionate. These included the propionate CoA-transferase, the lactoyl-CoA dehydratase, and the acryloyl-CoA reductase from Anaerotignum neopropionicum as well as a D-lactate dehydrogenase from Leuconostoc mesenteroides subsp. mesenteroides. Due to difficulties in assembling all genes on one plasmid under the control of standard promoters, the PtcdB-tcdR promoter system from Clostridium difficile was integrated into a two-plasmid system carrying the acrylate pathway genes. Several promoters were analyzed for their activity in C. saccharoperbutylacetonicum using the fluorescence-activating and absorption-shifting tag (FAST) as a fluorescent reporter to identify suitable candidates to drive tcdR expression. After selecting the lactose-inducible PbgaL promoter, engineered C. saccharoperbutylacetonicum strains produced 0.7 mM propionate upon induction of gene expression. The low productivity was suspected to be a consequence of a metabolic imbalance leading to acryloyl-CoA accumulation in the cells. To even out the proposed imbalance, the propionate-synthesis operons were rearranged, thereby increasing the propionate concentration by almost four-fold. This study is the first one to report recombinant propionate production using a clostridial host strain that has opened a new path towards bio-based propionate to be improved further in subsequent work. Key points • Determination of promoter activities in C. saccharoperbutylacetonicum using FAST. • Implementation of propionate production in C. saccharoperbutylacetonicum. • Elevation of propionate production by 375% to a concentration of 3 mM. Supplementary Information The online version contains supplementary material available at 10.1007/s00253-022-12210-8.
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Guo L, Sun L, Huo YX. Toward bioproduction of oxo chemicals from C1 feedstocks using isobutyraldehyde as an example. BIOTECHNOLOGY FOR BIOFUELS AND BIOPRODUCTS 2022; 15:80. [PMID: 35945564 PMCID: PMC9361566 DOI: 10.1186/s13068-022-02178-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 07/30/2022] [Indexed: 11/10/2022]
Abstract
AbstractOxo chemicals are valuable chemicals for synthesizing a wide array of industrial and consumer products. However, producing of oxo chemicals is predominately through the chemical process called hydroformylation, which requires petroleum-sourced materials and generates abundant greenhouse gas. Current concerns on global climate change have renewed the interest in reducing greenhouse gas emissions and recycling the plentiful greenhouse gas. A carbon–neutral manner in this regard is producing oxo chemicals biotechnologically using greenhouse gas as C1 feedstocks. Exemplifying isobutyraldehyde, this review demonstrates the significance of using greenhouse gas for oxo chemicals production. We highlight the current state and the potential of isobutyraldehyde synthesis with a special focus on the in vivo and in vitro scheme of C1-based biomanufacturing. Specifically, perspectives and scenarios toward carbon– and nitrogen–neutral isobutyraldehyde production are proposed. In addition, key challenges and promising approaches for enhancing isobutyraldehyde bioproduction are thoroughly discussed. This study will serve as a reference case in exploring the biotechnological potential and advancing oxo chemicals production derived from C1 feedstocks.
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Lauer I, Philipps G, Jennewein S. Metabolic engineering of Clostridium ljungdahlii for the production of hexanol and butanol from CO 2 and H 2. Microb Cell Fact 2022; 21:85. [PMID: 35568911 PMCID: PMC9107641 DOI: 10.1186/s12934-022-01802-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Accepted: 04/11/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The replacement of fossil fuels and petrochemicals with sustainable alternatives is necessary to mitigate the effects of climate change and also to counteract diminishing fossil resources. Acetogenic microorganisms such as Clostridium spp. are promising sources of fuels and basic chemical precursors because they efficiently utilize CO and CO2 as carbon source. However the conversion into high titers of butanol and hexanol is challenging. RESULTS Using a metabolic engineering approach we transferred a 17.9-kb gene cluster via conjugation, containing 13 genes from C. kluyveri and C. acetobutylicum for butanol and hexanol biosynthesis, into C. ljungdahlii. Plasmid-based expression resulted in 1075 mg L-1 butanol and 133 mg L-1 hexanol from fructose in complex medium, and 174 mg L-1 butanol and 15 mg L-1 hexanol from gaseous substrate (20% CO2 and 80% H2) in minimal medium. Product formation was increased by the genomic integration of the heterologous gene cluster. We confirmed the expression of all 13 enzymes by targeted proteomics and identified potential rate-limiting steps. Then, we removed the first-round selection marker using CRISPR/Cas9 and integrated an additional 7.8 kb gene cluster comprising 6 genes from C. carboxidivorans. This led to a significant increase in the hexanol titer (251 mg L-1) at the expense of butanol (158 mg L-1), when grown on CO2 and H2 in serum bottles. Fermentation of this strain at 2-L scale produced 109 mg L-1 butanol and 393 mg L-1 hexanol. CONCLUSIONS We thus confirmed the function of the butanol/hexanol biosynthesis genes and achieved hexanol biosynthesis in the syngas-fermenting species C. ljungdahlii for the first time, reaching the levels produced naturally by C. carboxidivorans. The genomic integration strain produced hexanol without selection and is therefore suitable for continuous fermentation processes.
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Affiliation(s)
- Ira Lauer
- Department for Industrial Biotechnology, Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Forckenbeckstr. 6, 52074, Aachen, Germany
| | - Gabriele Philipps
- Department for Industrial Biotechnology, Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Forckenbeckstr. 6, 52074, Aachen, Germany
| | - Stefan Jennewein
- Department for Industrial Biotechnology, Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Forckenbeckstr. 6, 52074, Aachen, Germany.
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Hu L, Guo S, Wang B, Fu R, Fan D, Jiang M, Fei Q, Gonzalez R. Bio-valorization of C1 gaseous substrates into bioalcohols: Potentials and challenges in reducing carbon emissions. Biotechnol Adv 2022; 59:107954. [DOI: 10.1016/j.biotechadv.2022.107954] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2021] [Revised: 03/29/2022] [Accepted: 04/04/2022] [Indexed: 11/02/2022]
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Hermann M, Teleki A, Weitz S, Niess A, Freund A, Bengelsdorf FR, Dürre P, Takors R. Identifying and Engineering Bottlenecks of Autotrophic Isobutanol Formation in Recombinant C. ljungdahlii by Systemic Analysis. Front Bioeng Biotechnol 2021; 9:647853. [PMID: 33748092 PMCID: PMC7968104 DOI: 10.3389/fbioe.2021.647853] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 02/09/2021] [Indexed: 11/13/2022] Open
Abstract
Clostridium ljungdahlii (C. ljungdahlii, CLJU) is natively endowed producing acetic acid, 2,3-butandiol, and ethanol consuming gas mixtures of CO2, CO, and H2 (syngas). Here, we present the syngas-based isobutanol formation using C. ljungdahlii harboring the recombinant amplification of the "Ehrlich" pathway that converts intracellular KIV to isobutanol. Autotrophic isobutanol production was studied analyzing two different strains in 3-L gassed and stirred bioreactors. Physiological characterization was thoroughly applied together with metabolic profiling and flux balance analysis. Thereof, KIV and pyruvate supply were identified as key "bottlenecking" precursors limiting preliminary isobutanol formation in CLJU[KAIA] to 0.02 g L-1. Additional blocking of valine synthesis in CLJU[KAIA]:ilvE increased isobutanol production by factor 6.5 finally reaching 0.13 g L-1. Future metabolic engineering should focus on debottlenecking NADPH availability, whereas NADH supply is already equilibrated in the current generation of strains.
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Affiliation(s)
- Maria Hermann
- Institute of Biochemical Engineering, Faculty of Energy-, Process-, and Bio-Engineering, University of Stuttgart, Stuttgart, Germany
| | - Attila Teleki
- Institute of Biochemical Engineering, Faculty of Energy-, Process-, and Bio-Engineering, University of Stuttgart, Stuttgart, Germany
| | - Sandra Weitz
- Institute of Microbiology and Biotechnology, Faculty of Natural Sciences, University of Ulm, Ulm, Germany
| | - Alexander Niess
- Institute of Biochemical Engineering, Faculty of Energy-, Process-, and Bio-Engineering, University of Stuttgart, Stuttgart, Germany
| | - Andreas Freund
- Institute of Biochemical Engineering, Faculty of Energy-, Process-, and Bio-Engineering, University of Stuttgart, Stuttgart, Germany
| | - Frank Robert Bengelsdorf
- Institute of Microbiology and Biotechnology, Faculty of Natural Sciences, University of Ulm, Ulm, Germany
| | - Peter Dürre
- Institute of Microbiology and Biotechnology, Faculty of Natural Sciences, University of Ulm, Ulm, Germany
| | - Ralf Takors
- Institute of Biochemical Engineering, Faculty of Energy-, Process-, and Bio-Engineering, University of Stuttgart, Stuttgart, Germany
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