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Ma JY, Yan Z, Sun XD, Jiang YQ, Duan JL, Feng LJ, Zhu FP, Liu XY, Xia PF, Yuan XZ. A hybrid photocatalytic system enables direct glucose utilization for methanogenesis. Proc Natl Acad Sci U S A 2024; 121:e2317058121. [PMID: 38232281 PMCID: PMC10823229 DOI: 10.1073/pnas.2317058121] [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: 10/04/2023] [Accepted: 11/20/2023] [Indexed: 01/19/2024] Open
Abstract
Integration of methanogenic archaea with photocatalysts presents a sustainable solution for solar-driven methanogenesis. However, maximizing CH4 conversion efficiency remains challenging due to the intrinsic energy conservation and strictly restricted substrates of methanogenic archaea. Here, we report a solar-driven biotic-abiotic hybrid (biohybrid) system by incorporating cadmium sulfide (CdS) nanoparticles with a rationally designed methanogenic archaeon Methanosarcina acetivorans C2A, in which the glucose synergist protein and glucose kinase, an energy-efficient route for glucose transport and phosphorylation from Zymomonas mobilis, were implemented to facilitate nonnative substrate glucose for methanogenesis. We demonstrate that the photo-excited electrons facilitate membrane-bound electron transport chain, thereby augmenting the Na+ and H+ ion gradients across membrane to enhance adenosine triphosphate (ATP) synthesis. Additionally, this biohybrid system promotes the metabolism of pyruvate to acetyl coenzyme A (AcCoA) and inhibits the flow of AcCoA to the tricarboxylic acid (TCA) cycle, resulting in a 1.26-fold augmentation in CH4 production from glucose-derived carbon. Our results provide a unique strategy for enhancing methanogenesis through rational biohybrid design and reprogramming, which gives a promising avenue for sustainably manufacturing value-added chemicals.
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Affiliation(s)
- Jing-Ya Ma
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Zhen Yan
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Xiao-Dong Sun
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Yu-Qian Jiang
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Jian-Lu Duan
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Li-Juan Feng
- College of Geography and Environment, Shandong Normal University, Jinan250014, People’s Republic of China
| | - Fan-Ping Zhu
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Xiao-Yu Liu
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Peng-Fei Xia
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
| | - Xian-Zheng Yuan
- Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao266237, People’s Republic of China
- Sino-French Research Institute for Ecology and Environment, Shandong University, Qingdao266237, People’s Republic of China
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Cofactor Self-Sufficient Whole-Cell Biocatalysts for the Relay-Race Synthesis of Shikimic Acid. FERMENTATION 2022. [DOI: 10.3390/fermentation8050229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Shikimic acid (SA) is a key intermediate in the aromatic amino-acid biosynthetic pathway, as well as an important precursor for synthesizing many valuable antiviral drugs. The asymmetric reduction of 3-dehydroshikimic acid (DHS) to SA is catalyzed by shikimate dehydrogenase (AroE) using NADPH as the cofactor; however, the intracellular NADPH supply limits the biosynthetic capability of SA. Glucose dehydrogenase (GDH) is an efficient enzyme which is typically used for NAD(P)H regeneration in biocatalytic processes. In this study, a series of NADPH self-sufficient whole-cell biocatalysts were constructed, and the biocatalyst co-expressing Bmgdh–aroE showed the highest conversion rate for the reduction of DHS to SA. Then, the preparation of whole-cell biocatalysts by fed-batch fermentation without supplementing antibiotics was developed on the basis of the growth-coupled l-serine auxotroph. After optimizing the whole-cell biocatalytic conditions, a titer of 81.6 g/L SA was obtained from the supernatant of fermentative broth in 98.4% yield (mol/mol) from DHS with a productivity of 40.8 g/L/h, and cofactor NADP+ or NADPH was not exogenously supplemented during the whole biocatalytic process. The efficient relay-race synthesis of SA from glucose by coupling microbial fermentation with a biocatalytic process was finally achieved. This work provides an effective strategy for the biosynthesis of fine chemicals that are difficult to obtain through de novo biosynthesis from renewable feedstocks, as well as for biocatalytic studies that strictly rely on NAD(P)H regeneration.
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Braga A, Gomes D, Rainha J, Amorim C, Cardoso BB, Gudiña EJ, Silvério SC, Rodrigues JL, Rodrigues LR. Zymomonas mobilis as an emerging biotechnological chassis for the production of industrially relevant compounds. BIORESOUR BIOPROCESS 2021; 8:128. [PMID: 38650193 PMCID: PMC10992037 DOI: 10.1186/s40643-021-00483-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Accepted: 12/06/2021] [Indexed: 11/10/2022] Open
Abstract
Zymomonas mobilis is a well-recognized ethanologenic bacterium with outstanding characteristics which make it a promising platform for the biotechnological production of relevant building blocks and fine chemicals compounds. In the last years, research has been focused on the physiological, genetic, and metabolic engineering strategies aiming at expanding Z. mobilis ability to metabolize lignocellulosic substrates toward biofuel production. With the expansion of the Z. mobilis molecular and computational modeling toolbox, the potential of this bacterium as a cell factory has been thoroughly explored. The number of genomic, transcriptomic, proteomic, and fluxomic data that is becoming available for this bacterium has increased. For this reason, in the forthcoming years, systems biology is expected to continue driving the improvement of Z. mobilis for current and emergent biotechnological applications. While the existing molecular toolbox allowed the creation of stable Z. mobilis strains with improved traits for pinpointed biotechnological applications, the development of new and more flexible tools is crucial to boost the engineering capabilities of this bacterium. Novel genetic toolkits based on the CRISPR-Cas9 system and recombineering have been recently used for the metabolic engineering of Z. mobilis. However, they are mostly at the proof-of-concept stage and need to be further improved.
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Affiliation(s)
- Adelaide Braga
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Daniela Gomes
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - João Rainha
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Cláudia Amorim
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Beatriz B Cardoso
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Eduardo J Gudiña
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Sara C Silvério
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Joana L Rodrigues
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
| | - Lígia R Rodrigues
- CEB-Centre of Biological Engineering, Universidade Do Minho, Campus de Gualtar, 4710-057, Braga, Portugal.
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Kurgan G, Onyeabor M, Holland SC, Taylor E, Schneider A, Kurgan L, Billings T, Wang X. Directed evolution of Zymomonas mobilis sugar facilitator Glf to overcome glucose inhibition. J Ind Microbiol Biotechnol 2021; 49:6371102. [PMID: 34529081 PMCID: PMC9118996 DOI: 10.1093/jimb/kuab066] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 09/04/2021] [Indexed: 12/01/2022]
Abstract
Cellular import of D-xylose, the second most abundant sugar in typical lignocellulosic biomass, has been evidenced to be an energy-depriving process in bacterial biocatalysts. The sugar facilitator of Zymomonas mobilis, Glf, is capable of importing xylose at high rates without extra energy input, but is inhibited by D-glucose (the primary biomass sugar), potentially limiting the utility of this transporter for fermentation of sugar mixtures derived from lignocellulose. In this work we developed an Escherichia coli platform strain deficient in glucose and xylose transport to facilitate directed evolution of Glf to overcome glucose inhibition. Using this platform, we isolated nine Glf variants created by both random and site-saturation mutagenesis with increased xylose utilization rates ranging from 4.8-fold to 13-fold relative to wild-type Glf when fermenting 100 g l–1 glucose–xylose mixtures. Diverse point mutations such as A165M and L445I were discovered leading to released glucose inhibition. Most of these mutations likely alter sugar coordinating pocket for the 6-hydroxymethyl group of D-glucose. These discovered glucose-resistant Glf variants can be potentially used as energy-conservative alternatives to the native sugar transport systems of bacterial biocatalysts for fermentation of lignocellulose-derived sugars.
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Affiliation(s)
- Gavin Kurgan
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Moses Onyeabor
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Steven C Holland
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Eric Taylor
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Aidan Schneider
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Logan Kurgan
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Tommy Billings
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
| | - Xuan Wang
- School of Life Sciences, Arizona State University, Tempe, Arizona, USA
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Folch PL, Bisschops MM, Weusthuis RA. Metabolic energy conservation for fermentative product formation. Microb Biotechnol 2021; 14:829-858. [PMID: 33438829 PMCID: PMC8085960 DOI: 10.1111/1751-7915.13746] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 12/16/2020] [Accepted: 12/21/2020] [Indexed: 12/02/2022] Open
Abstract
Microbial production of bulk chemicals and biofuels from carbohydrates competes with low-cost fossil-based production. To limit production costs, high titres, productivities and especially high yields are required. This necessitates metabolic networks involved in product formation to be redox-neutral and conserve metabolic energy to sustain growth and maintenance. Here, we review the mechanisms available to conserve energy and to prevent unnecessary energy expenditure. First, an overview of ATP production in existing sugar-based fermentation processes is presented. Substrate-level phosphorylation (SLP) and the involved kinase reactions are described. Based on the thermodynamics of these reactions, we explore whether other kinase-catalysed reactions can be applied for SLP. Generation of ion-motive force is another means to conserve metabolic energy. We provide examples how its generation is supported by carbon-carbon double bond reduction, decarboxylation and electron transfer between redox cofactors. In a wider perspective, the relationship between redox potential and energy conservation is discussed. We describe how the energy input required for coenzyme A (CoA) and CO2 binding can be reduced by applying CoA-transferases and transcarboxylases. The transport of sugars and fermentation products may require metabolic energy input, but alternative transport systems can be used to minimize this. Finally, we show that energy contained in glycosidic bonds and the phosphate-phosphate bond of pyrophosphate can be conserved. This review can be used as a reference to design energetically efficient microbial cell factories and enhance product yield.
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Affiliation(s)
- Pauline L. Folch
- Bioprocess EngineeringWageningen University & ResearchPost office box 16Wageningen6700 AAThe Netherlands
| | - Markus M.M. Bisschops
- Bioprocess EngineeringWageningen University & ResearchPost office box 16Wageningen6700 AAThe Netherlands
| | - Ruud A. Weusthuis
- Bioprocess EngineeringWageningen University & ResearchPost office box 16Wageningen6700 AAThe Netherlands
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Shanmugam KT, Ingram LO. Principles and practice of designing microbial biocatalysts for fuel and chemical production. J Ind Microbiol Biotechnol 2021; 49:6158391. [PMID: 33686428 PMCID: PMC9118985 DOI: 10.1093/jimb/kuab016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 03/03/2021] [Indexed: 11/14/2022]
Abstract
The finite nature of fossil fuels and the environmental impact of its use have raised interest in alternate renewable energy sources. Specifically, non-food carbohydrates, such as lignocellulosic biomass, can be used to produce next generation biofuels, including cellulosic ethanol and other non-ethanol fuels like butanol. However, currently there is no native microorganism that can ferment all lignocellulosic sugars to fuel molecules. Thus, research is focused on engineering improved microbial biocatalysts for production of liquid fuels at high productivity, titer and yield. A clear understanding and application of the basic principles of microbial physiology and biochemistry are crucial to achieve this goal. In this review, we present and discuss the construction of microbial biocatalysts that integrate these principles with ethanol-producing Escherichia coli as an example of metabolic engineering. These principles also apply to fermentation of lignocellulosic sugars to other chemicals that are currently produced from petroleum.
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Affiliation(s)
- K T Shanmugam
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
| | - Lonnie O Ingram
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
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Li Y, Sun Z, Xu Y, Luan Y, Xu J, Liang Q, Qi Q, Wang Q. Enhancing the Glucose Flux of an Engineered EP-Bifido Pathway for High Poly(Hydroxybutyrate) Yield Production. Front Bioeng Biotechnol 2020; 8:517336. [PMID: 32984296 PMCID: PMC7481327 DOI: 10.3389/fbioe.2020.517336] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Accepted: 08/12/2020] [Indexed: 11/25/2022] Open
Abstract
Background As the greenhouse effect becomes more serious and carbon dioxide emissions continue rise, the application prospects of carbon sequestration or carbon-saving pathways increase. Previously, we constructed an EP-bifido pathway in Escherichia coli by combining Embden-Meyerhof-Parnas pathway, pentose phosphate pathway and “bifid shunt” for high acetyl-CoA production. There is much room for improvement in the EP-bifido pathway, including in production of target compounds such as poly(hydroxybutyrate) (PHB). Result To optimize the EP-bifido pathway and obtain higher PHB yields, we knocked out the specific phosphoenolpyruvate phosphate transferase system (PTS) component II Cglc, encoded by ptsG. This severely inhibited the growth and sugar consumption of the bacterial cells. Subsequently, we used multiple automated genome engineering (MAGE) to optimize the ribosome binding site (RBS) sequences of galP (galactose: H (+) symporter) and glk (glucokinase gene bank: NC_017262.1), encoding galactose permease and glucokinase, respectively. Growth and glucose uptake were partially restored in the bacteria. Finally, we introduced the glf (UDP-galactopyranose) from Zymomonas mobilis mutase sugar transport vector into the host strain genome. Conclusion After optimizing RBS of galP, the resulting strain L-6 obtained a PHB yield of 71.9% (mol/mol) and a 76 wt% PHB content using glucose as the carbon source. Then when glf was integrated into the genome strain L-6, the resulting strain M-6 reached a 5.81 g/L PHB titer and 85.1 wt% PHB content.
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Affiliation(s)
- Ying Li
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Zhijie Sun
- Marine Biology Institute, Shantou University, Shantou, China
| | - Ya Xu
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Yaqi Luan
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Jiasheng Xu
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Quanfeng Liang
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Qingsheng Qi
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China.,CAS Key Lab of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
| | - Qian Wang
- National Glycoengineering Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
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Combination of the CRP mutation and ptsG deletion in Escherichia coli to efficiently synthesize xylitol from corncob hydrolysates. Appl Microbiol Biotechnol 2020; 104:2039-2050. [PMID: 31950219 DOI: 10.1007/s00253-019-10324-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 12/05/2019] [Accepted: 12/15/2019] [Indexed: 12/16/2022]
Abstract
The biotechnology-based production of xylitol has received widespread attention because it can use cheap and renewable lignocellulose as a raw material, thereby decreasing costs and pollution. The simultaneous use of various sugars in lignocellulose hydrolysates is a primary prerequisite for efficient xylitol production. In this study, a ΔptsG and crp* combinatorial strategy was used to generate Escherichia coli W3110 strain IS5-dI, which completely eliminated glucose repression and simultaneously used glucose and xylose. This strain produced 164 g/L xylitol from detoxified corncob hydrolysates during a fed-batch fermentation in a 15-L bioreactor, which was 14.7% higher than the xylitol produced by the starting strain, IS5-d (143 g/L), and the xylitol productivity was 3.04 g/L/h. These results represent the highest xylitol concentration and productivity reported to date for bacteria and hemicellulosic sugars. Additionally, strain IS5-dG, which differs from IS5-dI at CRP amino acid residue 127 (I127G), was tolerant to the toxins in corncob hydrolysates. In a fed-batch fermentation experiment involving a 15-L bioreactor, IS5-dG produced 137 g/L xylitol from non-detoxified corncob hydrolysates, with a productivity of 1.76 g/L/h. On the basis of these results, we believe that IS5-dI and IS5-dG may be useful host strains for the industrial-scale production of xylitol from detoxified or non-detoxified corncob hydrolysates.
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Zymomonas mobilis metabolism: Novel tools and targets for its rational engineering. Adv Microb Physiol 2020; 77:37-88. [PMID: 34756211 DOI: 10.1016/bs.ampbs.2020.08.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Zymomonas mobilis is an α-proteobacterium that interests the biofuel industry due to its perfect ethanol fermentation yields. From its first description as a bacterial isolate in fermented alcoholic beverages to date, Z. mobilis has been rigorously studied in directions basic and applied. The Z. mobilis powerful Entner-Doudoroff glycolytic pathway has been the center of rigorous biochemical studies and, aside from ethanol, it has attracted interest in terms of high-added-value chemical manufacturing. Energetic balances and the effects of respiration have been explored in fundamental directions as also in applications pursuing strain enhancement and the utilization of alternative carbon sources. Metabolic modeling has addressed the optimization of the biochemical circuitry at various conditions of growth and/or substrate utilization; it has been also critical in predicting desirable end-product yields via flux redirection. Lastly, stress tolerance has received particular attention, since it directly determines biocatalytical performance at challenging bioreactor conditions. At a genetic level, advances in the genetic engineering of the organism have brought forth beneficial manipulations in the Z. mobilis gene pool, e.g., knock-outs, knock-ins and gene stacking, aiming to broaden the metabolic repertoire and increase robustness. Recent omic and expressional studies shed light on the genomic content of the most applied strains and reveal landscapes of activity manifested at ambient or reactor-based conditions. Studies such as those reviewed in this work, contribute to the understanding of the biology of Z. mobilis, enable insightful strain development, and pave the way for the transformation of Z. mobilis into a consummate organism for biomass conversion.
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Tröndle J, Schoppel K, Bleidt A, Trachtmann N, Sprenger GA, Weuster-Botz D. Metabolic control analysis of L-tryptophan production with Escherichia coli based on data from short-term perturbation experiments. J Biotechnol 2019; 307:15-28. [PMID: 31639341 DOI: 10.1016/j.jbiotec.2019.10.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2019] [Accepted: 10/10/2019] [Indexed: 12/21/2022]
Abstract
E. coli strain NT1259 /pF112aroFBLkan was able to produce 14.3 g L-1 L-tryptophan within 68 h in a fed-batch process from glycerol on a 15 L scale. To gain detailed insight into metabolism of this E. coli strain in the fed-batch process, a sample of L-tryptophan producing cells was withdrawn after 47 h, was separated rapidly and then resuspended in four parallel stirred-tank bioreactors with fresh media. Four different carbon sources (glucose, glycerol, succinate, pyruvate) were supplied individually with varying feeding rates within 19 min and the metabolic reactions of the cells in the four parallel reactors were analyzed by quantification of extracellular and intracellular substrate, product and metabolite concentrations. Data analysis allowed the estimation of intracellular carbon fluxes and of thermodynamic limitations concerning intracellular concentrations and reaction energies. Carbon fluxes and intracellular metabolite concentrations enabled the estimation of elasticities and flux control coefficients by applying metabolic control analysis making use of a metabolic model considering 48 enzymatic reactions and 56 metabolites. As the flux control coefficients describe connections between enzyme activities and metabolic fluxes, they reveal genetic targets for strain improvement. Metabolic control analysis of the recombinant E. coli cells withdrawn from the fed-batch production process clearly indicated that (i) the supply of two precursors for L-tryptophan biosynthesis, L-serine and phosphoribosyl-pyrophosphate, as well as (ii) the formation of aromatic byproducts and (iii) the enzymatic steps of igps and trps2 within the L-tryptophan biosynthesis pathway have major impact on fed-batch production of L-tryptophan from glycerol and should be the targets for further strain improvements.
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Affiliation(s)
- Julia Tröndle
- Technical University of Munich, Institute of Biochemical Engineering, Boltzmannstr. 15, 85748, Garching, Germany
| | - Kristin Schoppel
- Technical University of Munich, Institute of Biochemical Engineering, Boltzmannstr. 15, 85748, Garching, Germany
| | - Arne Bleidt
- Technical University of Munich, Institute of Biochemical Engineering, Boltzmannstr. 15, 85748, Garching, Germany
| | - Natalia Trachtmann
- University of Stuttgart, Institute of Microbiology, Allmandring 31, 70569, Stuttgart, Germany
| | - Georg A Sprenger
- University of Stuttgart, Institute of Microbiology, Allmandring 31, 70569, Stuttgart, Germany
| | - Dirk Weuster-Botz
- Technical University of Munich, Institute of Biochemical Engineering, Boltzmannstr. 15, 85748, Garching, Germany.
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11
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Metabolic Engineering and Fermentation Process Strategies for L-Tryptophan Production by Escherichia coli. Processes (Basel) 2019. [DOI: 10.3390/pr7040213] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
L-tryptophan is an essential aromatic amino acid that has been widely used in medicine, food, and animal feed. Microbial biosynthesis of L-tryptophan through metabolic engineering approaches represents a sustainable, cost-effective, and environmentally friendly route compared to chemical synthesis. In particular, metabolic pathway engineering allows enhanced product titers by inactivating/blocking the competing pathways, increasing the intracellular level of essential precursors, and overexpressing rate-limiting enzymatic steps. Based on the route of the l-tryptophan biosynthesis pathway, this review presents a systematic and detailed summary of the contemporary metabolic engineering approaches employed for l-tryptophan production. In addition to the engineering of the l-tryptophan biosynthesis pathway, the metabolic engineering modification of carbon source uptake, by-product formation, key regulatory factors, and the polyhydroxybutyrate biosynthesis pathway in l-tryptophan biosynthesis are discussed. Moreover, fermentation bioprocess optimization strategies used for l-tryptophan overproduction are also delineated. Towards the end, the review is wrapped up with the concluding remarks, and future strategies are outlined for the development of a high l-tryptophan production strain.
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Kyselova L, Kreitmayer D, Kremling A, Bettenbrock K. Type and capacity of glucose transport influences succinate yield in two-stage cultivations. Microb Cell Fact 2018; 17:132. [PMID: 30153840 PMCID: PMC6112142 DOI: 10.1186/s12934-018-0980-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Accepted: 08/22/2018] [Indexed: 12/03/2022] Open
Abstract
Background Glucose is the main carbon source of E. coli and a typical substrate in production processes. The main glucose uptake system is the glucose specific phosphotransferase system (Glc-PTS). The PTS couples glucose uptake with its phosphorylation. This is achieved by the concomitant conversion of phosphoenolpyruvate (PEP) to pyruvate. The Glc-PTS is hence unfavorable for the production of succinate as this product is derived from PEP. Results We studied, in a systematic manner, the effect of knocking out the Glc-PTS and of replacing it with the glucose facilitator (Glf) of Zymomonas mobilis on succinate yield and productivity. For this study a set of strains derived from MG1655, carrying deletions of ackA-pta, adhE and ldhA that prevent the synthesis of competing fermentation products, were constructed and tested in two-stage cultivations. The data show that inactivation of the Glc-PTS achieved a considerable increase in succinate yield and productivity. On the other hand, aerobic growth of this strain on glucose was strongly decreased. Expression of the alternative glucose transporter, Glf, in this strain enhanced aerobic growth but productivity and yield under anaerobic conditions were slightly decreased. This decrease in succinate yield was accompanied by pyruvate production. Yield could be increased in both Glc-PTS mutants by overexpressing phosphoenolpyruvate carboxykinase (Pck). Productivity on the other hand, was decreased in the strain without alternative glucose transporter but strongly increased in the strain expressing Glf. The experiments were complemented by flux balance analysis in order to check the observed yields against the maximal theoretical yields. Furthermore, the phosphorylation state of EIIAGlc was determined. The data indicate that the ratio of PEP to pyruvate is correlating with pyruvate excretion. This ratio is affected by the PTS reaction as well as by further reactions at the PEP/pyruvate node. Conclusions The results show that for optimization of succinate yield and productivity it is not sufficient to knock out or introduce single reactions. Rather, balancing of the fluxes of central metabolism most important at the PEP/pyruvate node is important. Electronic supplementary material The online version of this article (10.1186/s12934-018-0980-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- L Kyselova
- Team Experimental Systems Biology, Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstr.1, 39106, Magdeburg, Germany
| | - D Kreitmayer
- Systembiotechnologie, Technische Universität München, Bolzmannstr. 15, 85748, Garching, Germany
| | - A Kremling
- Systembiotechnologie, Technische Universität München, Bolzmannstr. 15, 85748, Garching, Germany
| | - K Bettenbrock
- Team Experimental Systems Biology, Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstr.1, 39106, Magdeburg, Germany.
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Panichkin VB, Livshits VA, Biryukova IV, Mashko SV. Metabolic engineering of Escherichia coli for L-tryptophan production. APPL BIOCHEM MICRO+ 2017. [DOI: 10.1134/s0003683816090052] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Zhang L, Wang X, Yu M, Qiao Y, Zhang XH. Genomic analysis of Luteimonas abyssi XH031(T): insights into its adaption to the subseafloor environment of South Pacific Gyre and ecological role in biogeochemical cycle. BMC Genomics 2015; 16:1092. [PMID: 26690083 PMCID: PMC4687298 DOI: 10.1186/s12864-015-2326-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 12/15/2015] [Indexed: 01/22/2023] Open
Abstract
Background Luteimonas abyssi XH031T, which was previously isolated from subseafloor environment of the South Pacific Gyre (SPG), was an aerobic, gram-negative bacterium, and was identified to be a novel species of the genus Luteimonas in the family of Xanthomonadaceae. The nutrients utilization and metabolic mechanisms of XH031T indicate its plasticity. In view of the above characteristics, its genome was sequenced, and an in-depth analysis of the XH031T genome was performed to elucidate its adaption to extreme ecological environment. Results Various macromolecules including polysaccharide, protein, lipid and DNA could be degraded at low temperature by XH031T under laboratory conditions, and its degradation abilities to starch, gelatin and casein were considerably strong. Genome sequence analysis indicated that XH031T possesses extensive enzyme-encoding genes compared with four other Luteimonas strains. In addition, intricate systems (such as two-component regulatory systems, secretion systems, etc.), which are often used by bacteria to modulate the interactions of bacteria with their environments, were predicted in the genome of XH031T. Genes encoding a choline-glycine betaine transporter and 99 extracellular peptidases featured with halophilicity were predicted in the genome, which might help the bacterium to adapt to the salty marine environment. Moreover, there were many gene clusters in the genome encoding ATP-binding cassette superfamily transporters, major facilitator superfamily transporters and cytochrome P450s that might function in the process of various substrate transportation and metabolisms. Furthermore, drug resistance genes harbored in the genome might signify that XH031T has evolved hereditary adaptation to toxic environment. Finally, the annotation of metabolic pathways of the elements (such as carbon, nitrogen, sulfur, phosphor and iron) in the genome elucidated the degradation of organic matter in the deep sediment of the SPG. Conclusions The genome analysis showed that XH031T had genetic advantages to adapt to subseafloor environment. The material metabolism manifests that the strain may play an important ecological role in the biogeochemical cycle of the SPG, and various cold-adapted extracelluar enzymes produced by the strain may have significant value in application. Electronic supplementary material The online version of this article (doi:10.1186/s12864-015-2326-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Li Zhang
- College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao, 266003, China. .,College of Life Science, Qingdao Agriculture University, Qingdao, 266109, China.
| | - Xiaolei Wang
- College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao, 266003, China.
| | - Min Yu
- College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao, 266003, China.
| | - Yanlu Qiao
- College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao, 266003, China.
| | - Xiao-Hua Zhang
- College of Marine Life Sciences, Ocean University of China, 5 Yushan Road, Qingdao, 266003, China.
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Vargas-Tah A, Gosset G. Production of Cinnamic and p-Hydroxycinnamic Acids in Engineered Microbes. Front Bioeng Biotechnol 2015; 3:116. [PMID: 26347861 PMCID: PMC4542537 DOI: 10.3389/fbioe.2015.00116] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 07/30/2015] [Indexed: 11/13/2022] Open
Abstract
The aromatic compounds cinnamic and p-hydroxycinnamic acids (pHCAs) are phenylpropanoids having applications as precursors for the synthesis of thermoplastics, flavoring, cosmetic, and health products. These two aromatic acids can be obtained by chemical synthesis or extraction from plant tissues. However, both manufacturing processes have shortcomings, such as the generation of toxic subproducts or a low concentration in plant material. Alternative production methods are being developed to enable the biotechnological production of cinnamic and (pHCAs) by genetically engineering various microbial hosts, including Escherichia coli, Saccharomyces cerevisiae, Pseudomonas putida, and Streptomyces lividans. The natural capacity to synthesize these aromatic acids is not existent in these microbial species. Therefore, genetic modification have been performed that include the heterologous expression of genes encoding phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities, which catalyze the conversion of l-phenylalanine (l-Phe) and l-tyrosine (l-Tyr) to cinnamic acid and (pHCA), respectively. Additional host modifications include the metabolic engineering to increase carbon flow from central metabolism to the l-Phe or l-Tyr biosynthetic pathways. These strategies include the expression of feedback insensitive mutant versions of enzymes from the aromatic pathways, as well as genetic modifications to central carbon metabolism to increase biosynthetic availability of precursors phosphoenolpyruvate and erythrose-4-phosphate. These efforts have been complemented with strain optimization for the utilization of raw material, including various simple carbon sources, as well as sugar polymers and sugar mixtures derived from plant biomass. A systems biology approach to production strains characterization has been limited so far and should yield important data for future strain improvement.
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Affiliation(s)
- Alejandra Vargas-Tah
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México , Cuernavaca , Mexico
| | - Guillermo Gosset
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México , Cuernavaca , Mexico
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Increasing succinic acid production using the PTS-independent glucose transport system in a Corynebacterium glutamicum PTS-defective mutant. ACTA ACUST UNITED AC 2015; 42:1073-82. [DOI: 10.1007/s10295-015-1630-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 04/28/2015] [Indexed: 12/29/2022]
Abstract
Abstract
Succinic acid synthesized from glucose shows potential as a bio-based platform chemical. However, the need for a high glucose concentration, and the accompanying low yields, limit its industrial applications. Despite efficient glucose uptake by the phosphotransferase system (PTS), 1 mol of phosphoenolpyruvate is required for each mole of internalized glucose. Therefore, a PTS-defective Corynebacterium glutamicum mutant was constructed to increase phosphoenolpyruvate availability for succinic acid synthesis, resulting in a lower glucose utilization rate and slower growth. The transcriptional regulator iolR was also deleted to enable the PTS-defective mutant to utilize glucose via iolT-mediated glucose transport. Deletion of iolR and overexpression of iolT1 and ppgk (polyphosphate glucokinase) in the PTS-deficient C. glutamicum strain completely restored glucose utilization, increasing production by 11.6 % and yield by 32.4 % compared with the control. This study revealed for the first time that iolR represses the expression of the two glucokinase genes (glk and ppgk).
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17
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The transport and mediation mechanisms of the common sugars in Escherichia coli. Biotechnol Adv 2014; 32:905-19. [DOI: 10.1016/j.biotechadv.2014.04.009] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 03/23/2014] [Accepted: 04/18/2014] [Indexed: 11/17/2022]
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18
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Liu SP, Liu RX, Xiao MR, Zhang L, Ding ZY, Gu ZH, Shi GY. A systems level engineered E. coli capable of efficiently producing L-phenylalanine. Process Biochem 2014. [DOI: 10.1016/j.procbio.2014.01.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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19
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Yuzbashev TV, Vybornaya TV, Larina AS, Gvilava IT, Voyushina NE, Mokrova SS, Yuzbasheva EY, Manukhov IV, Sineoky SP, Debabov VG. Directed modification of Escherichia coli metabolism for the design of threonine-producing strains. APPL BIOCHEM MICRO+ 2013. [DOI: 10.1134/s0003683813090056] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Recruiting alternative glucose utilization pathways for improving succinate production. Appl Microbiol Biotechnol 2012; 97:2513-20. [PMID: 22895848 DOI: 10.1007/s00253-012-4344-1] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Revised: 07/28/2012] [Accepted: 07/30/2012] [Indexed: 01/14/2023]
Abstract
The phosphoenolpyruvate (PEP): carbohydrate phosphotransferase system (PTS) of Escherichia coli was usually inactivated to increase PEP supply for succinate production. However, cell growth and glucose utilization rate decreased significantly with PTS inactivation. In this work, two glucose transport proteins and two glucokinases (Glk) from E. coli and Zymomonas mobilis were recruited in PTS(-) strains, and their impacts on glucose utilization and succinate production were compared. All PTS(-) strains recruiting Z. mobilis glucose facilitator Glf had higher glucose utilization rates than PTS(-) strains using E. coli galactose permease (GalP), which was suggested to be caused by higher glucose transport velocity and lower energetic cost of Glf. The highest rate obtained by combinatorial modulation of glf and glk E. coli (2.13 g/L•h) was 81 % higher than the wild-type E. coli and 30 % higher than the highest rate obtained by combinatorial modulation of galP and glk E. coli . On the other hand, although glucokinase activities increased after replacing E. coli Glk with isoenzyme of Z. mobilis, glucose utilization rate decreased to 0.58 g/L•h, which was assumed due to tight regulation of Z. mobilis Glk by energy status of the cells. For succinate production, using GalP led to a 20 % increase in succinate productivity, while recruiting Glf led to a 41 % increase. These efficient alternative glucose utilization pathways obtained in this work can also be used for production of many other PEP-derived chemicals, such as malate, fumarate, and aromatic compounds.
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Chávez-Béjar MI, Báez-Viveros JL, Martínez A, Bolívar F, Gosset G. Biotechnological production of l-tyrosine and derived compounds. Process Biochem 2012. [DOI: 10.1016/j.procbio.2012.04.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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22
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Lindner SN, Seibold GM, Henrich A, Krämer R, Wendisch VF. Phosphotransferase system-independent glucose utilization in corynebacterium glutamicum by inositol permeases and glucokinases. Appl Environ Microbiol 2011; 77:3571-81. [PMID: 21478323 PMCID: PMC3127631 DOI: 10.1128/aem.02713-10] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 03/26/2011] [Indexed: 12/30/2022] Open
Abstract
Phosphoenolpyruvate-dependent glucose phosphorylation via the phosphotransferase system (PTS) is the major path of glucose uptake in Corynebacterium glutamicum, but some growth from glucose is retained in the absence of the PTS. The growth defect of a deletion mutant lacking the general PTS component HPr in glucose medium could be overcome by suppressor mutations leading to the high expression of inositol utilization genes or by the addition of inositol to the growth medium if a glucokinase is overproduced simultaneously. PTS-independent glucose uptake was shown to require at least one of the inositol transporters IolT1 and IolT2 as a mutant lacking IolT1, IolT2, and the PTS component HPr could not grow with glucose as the sole carbon source. Efficient glucose utilization in the absence of the PTS necessitated the overexpression of a glucokinase gene in addition to either iolT1 or iolT2. IolT1 and IolT2 are low-affinity glucose permeases with K(s) values of 2.8 and 1.9 mM, respectively. As glucose uptake and phosphorylation via the PTS differs from glucose uptake via IolT1 or IolT2 and phosphorylation via glucokinase by the requirement for phosphoenolpyruvate, the roles of the two pathways for l-lysine production were tested. The l-lysine yield by C. glutamicum DM1729, a rationally engineered l-lysine-producing strain, was lower than that by its PTS-deficient derivate DM1729Δhpr, which, however, showed low production rates. The combined overexpression of iolT1 or iolT2 with ppgK, the gene for PolyP/ATP-dependent glucokinase, in DM1729Δhpr enabled l-lysine production as fast as that by the parent strain DM1729 but with 10 to 20% higher l-lysine yield.
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Affiliation(s)
- Steffen N. Lindner
- Chair of Genetics of Prokaryotes, Faculty of Biology & CeBiTec, Bielefeld University, D-33501 Bielefeld, Germany
| | - Gerd M. Seibold
- Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany
| | - Alexander Henrich
- Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany
| | - Reinhard Krämer
- Institute of Biochemistry, University of Cologne, D-50674 Cologne, Germany
| | - Volker F. Wendisch
- Chair of Genetics of Prokaryotes, Faculty of Biology & CeBiTec, Bielefeld University, D-33501 Bielefeld, Germany
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23
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Ji XJ, Nie ZK, Huang H, Ren LJ, Peng C, Ouyang PK. Elimination of carbon catabolite repression in Klebsiella oxytoca for efficient 2,3-butanediol production from glucose-xylose mixtures. Appl Microbiol Biotechnol 2010; 89:1119-25. [PMID: 20957355 DOI: 10.1007/s00253-010-2940-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Revised: 10/03/2010] [Accepted: 10/07/2010] [Indexed: 10/18/2022]
Abstract
Microbial preference for glucose implies incomplete and/or slow utilization of lignocellulose hydrolysates, which is caused by the regulatory mechanism named carbon catabolite repression (CCR). In this study, a 2,3-butanediol (2,3-BD) producing Klebsiella oxytoca strain was engineered to eliminate glucose repression of xylose utilization. The crp(in) gene, encoding the mutant cyclic adenosine monophosphate (cAMP) receptor protein CRP(in), which does not require cAMP for functioning, was characterized and overexpressed in K. oxytoca. The engineered recombinant could utilize a mixture of glucose and xylose simultaneously, without CCR. The profiles of sugar consumption and 2,3-BD production by the engineered recombinant, in glucose and xylose mixtures, were examined and showed that glucose and xylose could be consumed simultaneously to produce 2,3-BD. This study offers a metabolic engineering strategy to achieve highly efficient utilization of sugar mixtures derived from the lignocellulosic biomass for the production of bio-based chemicals using enteric bacteria.
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Affiliation(s)
- Xiao-Jun Ji
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, No. 5 Xinmofan Road, Nanjing 210009, People's Republic of China
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24
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Engineering cyanobacteria to synthesize and export hydrophilic products. Appl Environ Microbiol 2010; 76:3462-6. [PMID: 20363793 DOI: 10.1128/aem.00202-10] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Metabolic engineering of cyanobacteria has the advantage that sunlight and CO(2) are the sole source of energy and carbon for these organisms. However, as photoautotrophs, cyanobacteria generally lack transporters to move hydrophilic primary metabolites across membranes. To address whether cyanobacteria could be engineered to produce and secrete organic primary metabolites, Synechococcus elongatus PCC7942 was engineered to express genes encoding an invertase and a glucose facilitator, which mediated secretion of glucose and fructose. Similarly, expression of lactate dehydrogenase- and lactate transporter-encoding genes allowed lactate accumulation in the extracellular medium. Expression of the relevant transporter was essential for secretion. Production of these molecules was further improved by expression of additional heterologous enzymes. Sugars secreted by the engineered cyanobacteria could be used to support Escherichia coli growth in the absence of additional nutrient sources. These results indicate that cyanobacteria can be engineered to produce and secrete high-value hydrophilic products.
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25
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Snoep JL, Arfman N, Yomano LP, Westerhoff HV, Conway T, Ingram LO. Control of glycolytic flux in Zymomonas mobilis by glucose 6-phosphate dehydrogenase activity. Biotechnol Bioeng 2009; 51:190-7. [PMID: 18624328 DOI: 10.1002/(sici)1097-0290(19960720)51:2<190::aid-bit8>3.0.co;2-e] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Glycolytic genes in Zymomonas mobilis are highly expressed and constitute half of the cytoplasmic protein. The first four genes (glf, zwf, edd, glk) in this pathway form an operon encoding a glucose permease, glucose 6-phosphate dehydrogenase (G6-P dehydrogenase), 6-phosphogluconate dehydratase, and glucokinase, respectively. Each gene was overexpressed from a tac promoter to investigate the control of glycolysis during the early stages of batch fermentation when flux (qCO(2)) is highest. Almost half of flux control appears to reside with G6-P dehydrogenase (C(J) (G6-P dehydrogenase) = 0.4). Although Z. mobilis exhibits one of the highest rates of glycolysis known, recombinants with elevated G6-P dehydrogenase had a 10% to 13% higher glycolytic flux than the native organism. A small increase in flux was also observed for recombinants expressing glf. Results obtained did not allow a critical evaluation of glucokinase and this enzyme may also represent an important control point. 6-Phosphogluconate dehydratase appears to be saturating at native levels. With constructs containing the full operon, growth rate and flux were both reduced, complicating interpretations. However, results obtained were also consistent with G6-P dehydrogenase as a primary site of control. Flux was 17% higher in operon constructs which exhibited a 17% increase in G6-P dehydrogenase specific activity, relative to the average of other operon constructs which contain a frameshift mutation in zwf. It is unlikely that all flux control residues solely in G6-P dehydrogenase (calculated C(J) (G6-P dehydrogenase) = 1.0) although these results further support the importance of this enzyme. As reported in previous studies, changes in flux were not accompanied by changes in growth rate providing further evidence that ATP production does not limit biosynthesis in rich complex medium.
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Affiliation(s)
- J L Snoep
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
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26
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Jahreis K, Pimentel-Schmitt EF, Brückner R, Titgemeyer F. Ins and outs of glucose transport systems in eubacteria. FEMS Microbiol Rev 2008; 32:891-907. [PMID: 18647176 DOI: 10.1111/j.1574-6976.2008.00125.x] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Glucose is the classical carbon source that is used to investigate the transport, metabolism, and regulation of nutrients in bacteria. Many physiological phenomena like nutrient limitation, stress responses, production of antibiotics, and differentiation are inextricably linked to nutrition. Over the years glucose transport systems have been characterized at the molecular level in more than 20 bacterial species. This review aims to provide an overview of glucose uptake systems found in the eubacterial kingdom. In addition, it will highlight the diverse and sophisticated regulatory features of glucose transport systems.
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Affiliation(s)
- Knut Jahreis
- Department of Biology and Chemistry, University of Osnabrück, Osnabrück, Germany
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27
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Proteomic investigation on the pyk-F gene knockout Escherichia coli for aromatic amino acid production. Enzyme Microb Technol 2007. [DOI: 10.1016/j.enzmictec.2007.03.018] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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28
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Ran N, Frost JW. Directed Evolution of 2-Keto-3-deoxy-6-phosphogalactonate Aldolase To Replace 3-Deoxy-d-arabino-heptulosonic Acid 7-Phosphate Synthase. J Am Chem Soc 2007; 129:6130-9. [PMID: 17451239 DOI: 10.1021/ja067330p] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Directed evolution of 2-keto-3-deoxy-6-phosphogalactonate (KDPGal) aldolase for microbial synthesis of shikimate pathway products provides an alternate strategy to circumvent the competition for phosphoenolpyruvate between 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) synthase and the phosphoenolpyruvate:carbohydrate phosphotransferase system in Escherichia coli. E. coli KDPGal aldolase was evolved using a combination of error-prone polymerase chain reaction, DNA shuffling, and multiple-site-directed mutagenesis to afford KDPGal aldolase variant NR8.276-2, which exhibits a 60-fold improvement in the ratio kcat/KM relative to that of wild-type E. coli KDPGal aldolase in catalyzing the addition of pyruvate to d-erythrose 4-phosphate to form DAHP. On the basis of its nucleotide sequence, NR8.276-2 contains seven amino acid changes from the wild-type E. coli KDPGal aldolase. Amplified expression of NR8.276-2 in the DAHP synthase and shikimate dehydrogenase-deficient E. coli strain NR7 under fed-batch fermentor-controlled cultivation conditions resulted in synthesis of 13 g/L 3-dehydroshikimic acid in 6.5% molar yield from glucose. Increased coexpression of the irreversible downstream enzyme 3-dehydroquinate synthase increased production of 3-dehydroshikimic acid to 19 g/L in 9.7% molar yield from glucose. Coamplification with transketolase, which increases d-erythrose 4-phosphate availability, afforded 16 g/L 3-dehydroshikimic acid in 8.5% molar yield.
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Affiliation(s)
- Ningqing Ran
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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Sprenger GA. From scratch to value: engineering Escherichia coli wild type cells to the production of l-phenylalanine and other fine chemicals derived from chorismate. Appl Microbiol Biotechnol 2007; 75:739-49. [PMID: 17435995 DOI: 10.1007/s00253-007-0931-y] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2007] [Revised: 03/06/2007] [Accepted: 03/06/2007] [Indexed: 11/28/2022]
Abstract
Recombinant strains of Escherichia coli K-12 for the production of the three aromatic amino acids (L-phenylalanine, L-tryptophan, L-tyrosine) have been constructed. The largest demand is for L-phenylalanine (L-Phe), as it can be used as a building block for the low-calorie sweetener, aspartame. Besides L-Phe, an increasing number of shikimic acid pathway intermediates can be produced from appropriate E. coli mutants with blocks in this pathway. The last common intermediate, chorismate, in E. coli not only serves for production of aromatic amino acids but can also be used for high-titer production of non-aromatic compounds, e.g., cyclohexadiene-transdiols. In an approach to diversity-oriented metabolic engineering (metabolic grafting), platform strains with increased flux through the general aromatic pathway were created by suitable gene deletions, additions, or rearrangements. Examples for rational strain constructions for L-phenylalanine and chorismate derivatives are given with emphasis on genetic engineering. As a result, L-phenylalanine producers are available, which were derived through several defined steps from E. coli K-12 wild type. These mutant strains showed L-phenylalanine titers of up to 38 g/l of L-phenylalanine (and up to 45.5 g/l using in situ product recovery). Likewise, two cyclohexadiene-transdiols could be recovered.
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Affiliation(s)
- Georg A Sprenger
- Institute of Microbiology, Universität Stuttgart, Allmandring 31, 70569 Stuttgart, Germany.
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Cirino PC, Chin JW, Ingram LO. EngineeringEscherichia colifor xylitol production from glucose-xylose mixtures. Biotechnol Bioeng 2006; 95:1167-76. [PMID: 16838379 DOI: 10.1002/bit.21082] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The range of value-added chemicals produced by Escherichia coli from simple sugars has been expanded to include xylitol. This was accomplished by screening the in vivo activity of a number of heterologous xylitol-producing enzymes. Xylose reductases from Candida boidinii (CbXR), Candida tenuis (CtXR), Pichia stipitis (PsXR), and Saccharmoyces cerivisiae (ScXR), and xylitol dehydrogenases from Gluconobacter oxydans (GoXDH) and Pichia stipitis (PsXDH) were all functional in E. coli to varying extents. Replacement of E. coli's native cyclic AMP receptor protein (CRP) with a cyclic AMP-independent mutant (CRP*) facilitated xylose uptake and xylitol production from mixtures of glucose and xylose, with glucose serving as the growth substrate and source of reducing equivalents. Of the enzymes tested, overexpression of NADPH-dependent CbXR produced the highest concentrations of xylitol in shake-flask cultures (approximately 275 mM in LB cultures, approximately 180 mM using minimal medium). Expression of CbXR in strain PC09 (crp*, DeltaxylB) in a 10-L controlled fermentation containing minimal medium resulted in production of approximately 250 mM xylitol (38 g/L), with concomitant utilization of approximately 150 mM glucose. The ratio of moles xylitol produced (from xylose) per mole glucose consumed was improved to > 3.7:1 using metabolically active "resting" cells.
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Affiliation(s)
- Patrick C Cirino
- Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Abstract
The ethanol-producing bacterium Zymomonas mobilis can serve as a model organism for the study of rapid catabolism and inefficient energy conversion in bacteria. Some basic aspects of its physiology still remain poorly understood. Here, the energy-spilling pathways during uncoupled growth, the structure and function of electron transport chain, and the possible reasons for the inefficient oxidative phosphorylation are analysed. Also, the interaction between ethanol synthesis and respiration is considered. The search for mechanisms of futile transmembrane proton cycling, as well as identification of respiratory electron transport complexes, like the energy-coupling NAD(P)H:quinone oxidoreductase and the cyanide-sensitive terminal oxidase(s), are outlined as the key problems for further research of Z. mobilis energy metabolism.
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Affiliation(s)
- Uldis Kalnenieks
- Institute of Microbiology and Biotechnology, Chair of Microbiology and Biotechnology, University of Latvia, Kronvalda boulv. 4, Riga, LV-1586, Latvia
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Gosset G. Improvement of Escherichia coli production strains by modification of the phosphoenolpyruvate:sugar phosphotransferase system. Microb Cell Fact 2005; 4:14. [PMID: 15904518 PMCID: PMC1156936 DOI: 10.1186/1475-2859-4-14] [Citation(s) in RCA: 200] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Accepted: 05/16/2005] [Indexed: 12/22/2022] Open
Abstract
The application of metabolic engineering in Escherichia coli has resulted in the generation of strains with the capacity to produce metabolites of commercial interest. Biotechnological processes with these engineered strains frequently employ culture media containing glucose as the carbon and energy source. In E. coli, the phosphoenolpyruvate:sugar phosphotransferase system (PTS) transports glucose when this sugar is present at concentrations like those used in production fermentations. This protein system is involved in phosphoenolpyruvate-dependent sugar transport, therefore, its activity has an important impact on carbon flux distribution in the phosphoenolpyruvate and pyruvate nodes. Furthermore, PTS has a very important role in carbon catabolite repression. The properties of PTS impose metabolic and regulatory constraints that can hinder strain productivity. For this reason, PTS has been a target for modification with the purpose of strain improvement. In this review, PTS characteristics most relevant to strain performance and the different strategies of PTS modification for strain improvement are discussed. Functional replacement of PTS by alternative phosphoenolpyruvate-independent uptake and phosphorylation activities has resulted in significant improvements in product yield from glucose and productivity for several classes of metabolites. In addition, inactivation of PTS components has been applied successfully as a strategy to abolish carbon catabolite repression, resulting in E. coli strains that use more efficiently sugar mixtures, such as those obtained from lignocellulosic hydrolysates.
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Affiliation(s)
- Guillermo Gosset
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo, Postal 510-3, Cuernavaca, Mor, 62250, México.
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Polen T, Krämer M, Bongaerts J, Wubbolts M, Wendisch VF. The global gene expression response of Escherichia coli to l-phenylalanine. J Biotechnol 2005; 115:221-37. [PMID: 15639085 DOI: 10.1016/j.jbiotec.2004.08.017] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2004] [Revised: 07/29/2004] [Accepted: 08/19/2004] [Indexed: 10/26/2022]
Abstract
We investigated the global gene expression changes of Escherichia coli due to the presence of different concentrations of phenylalanine or shikimate in the growth medium. The response to 0.5 g l(-1) phenylalanine primarily reflected a perturbed aromatic amino acid metabolism, in particular due to TyrR-mediated regulation. The addition of 5g l(-1) phenylalanine reduced the growth rate by half and elicited a great number of likely indirect effects on genes regulated in response to changed pH, nitrogen or carbon availability. Consistent with the observed gene expression changes, supplementation with shikimate, tyrosine and tryptophan relieved growth inhibition by phenylalanine. In contrast to the wild-type, a tyrR disruption strain showed increased expression of pckA and of tktB in the presence of phenylalanine, but its growth was not affected by phenylalanine at the concentrations tested. The absence of growth inhibition by phenylalanine suggested that at high phenylalanine concentrations TyrR-defective strains might perform better in phenylalanine production.
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Affiliation(s)
- T Polen
- Institut für Biotechnologie 1, Forschungszentrum Jülich, D-52425 Jülich, Germany.
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Hernández-Montalvo V, Martínez A, Hernández-Chavez G, Bolivar F, Valle F, Gosset G. Expression of galP and glk in a Escherichia coli PTS mutant restores glucose transport and increases glycolytic flux to fermentation products. Biotechnol Bioeng 2003; 83:687-94. [PMID: 12889033 DOI: 10.1002/bit.10702] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
In Escherichia coli, the uptake and phosphorylation of glucose is carried out mainly by the phosphotransferase system (PTS). Despite the efficiency of glucose transport by PTS, the required consumption of 1 mol of phosphoenolpyruvate (PEP) for each mol of internalized glucose represents a drawback for some biotechnological applications where PEP is a precursor of the desired product. For this reason, there is considerable interest in the generation of strains that can transport glucose efficiently by a non-PTS mechanism. The purpose of this work was to study the effect of different gene expression levels, of galactose permease (GalP) and glucokinase (Glk), on glucose internalization and phosphorylation in a E. coli PTS(-) strain. The W3110 PTS(-), designated VH32, showed limited growth on glucose with a specific growth rate (mu) of 0.03 h(-1). A low copy plasmid family was constructed containing E. coli galP and glk genes, individually or combined, under the control of a trc-derived promoter set. This plasmid family was used to transform the VH32 strain, each plasmid having different levels of expression of galP and glk. Experiments in minimal medium with glucose showed that expression of only galP under the control of a wild-type trc promoter resulted in a mu of 0.55 h(-1), corresponding to 89% of the mu measured for W3110 (0.62 h(-1)). In contrast, no increase in specific growth rate (mu) was observed in VH32 with a plasmid expressing only glk from the same promoter. Strains transformed with part of the plasmid family, containing both galP and glk genes, showed a mu value similar to that of W3110. Fermentor experiments with the VH32 strain harboring plasmids pv1Glk1GalP, pv4Glk5GalP, and pv5Glk5GalP showed that specific acetate productivity was twofold higher than in W3110. Introduction of plasmid pLOI1594, coding for pyruvate decarboxylase and alcohol dehydrogenase from Zymomonas mobilis, to strain VH32 carrying one of the plasmids with galP and glk caused a twofold increase in ethanol productivity over strain W3110, also containing pLOI1594.
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Affiliation(s)
- Verónica Hernández-Montalvo
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, UNAM AP 510-3, Cuernavaca, Morelos 62271, México
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Bongaerts J, Krämer M, Müller U, Raeven L, Wubbolts M. Metabolic engineering for microbial production of aromatic amino acids and derived compounds. Metab Eng 2001; 3:289-300. [PMID: 11676565 DOI: 10.1006/mben.2001.0196] [Citation(s) in RCA: 215] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Metabolic engineering to design and construct microorganisms suitable for the production of aromatic amino acids and derivatives thereof requires control of a complicated network of metabolic reactions that partly act in parallel and frequently are in rapid equilibrium. Engineering the regulatory circuits, the uptake of carbon, the glycolytic pathway, the pentose phosphate pathway, and the common aromatic amino acid pathway as well as amino acid importers and exporters that have all been targeted to effect higher productivities of these compounds are discussed.
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Affiliation(s)
- J Bongaerts
- DSM Biotech GmbH, Karl-Heinz-Beckurts-Strasse 13, D-52428 Jülich, Germany
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Gibson JM, Thomas PS, Thomas JD, Barker JL, Chandran SS, Harrup MK, Draths KM, Frost JW. Benzene-Free Synthesis of Phenol. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3773(20010518)40:10<1945::aid-anie1945>3.0.co;2-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gibson JM, Thomas PS, Thomas JD, Barker JL, Chandran SS, Harrup MK, Draths KM, Frost JW. Benzene-Free Synthesis of Phenol. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010518)113:10<1999::aid-ange1999>3.0.co;2-a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Sprenger GA. Carbohydrate metabolism inZymomonas mobilis: a catabolic highway with some scenic routes. FEMS Microbiol Lett 1996. [DOI: 10.1111/j.1574-6968.1996.tb08593.x] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Basic and applied aspects of metabolic diversity: The phosphoenolpyruvate node. J Ind Microbiol Biotechnol 1996. [DOI: 10.1007/bf01574776] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Weisser P, Krämer R, Sprenger GA. Expression of the Escherichia coli pmi gene, encoding phosphomannose-isomerase in Zymomonas mobilis, leads to utilization of mannose as a novel growth substrate, which can be used as a selective marker. Appl Environ Microbiol 1996; 62:4155-61. [PMID: 8900006 PMCID: PMC168237 DOI: 10.1128/aem.62.11.4155-4161.1996] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Wild-type Zymomonas mobilis can utilize only three substrates (sucrose, glucose, and fructose) as sole carbon sources, which are largely converted into ethanol and carbon dioxide. Here, we show that although D-mannose is not used as a growth substrate, it is taken up via the glucose uniport system (glucose facilitator protein) with a Vmax similar to that of glucose. Moreover, D-mannose was phosphorylated by a side activity of the resident fructokinase to mannose-6-phosphate. Fructokinase was purified to homogeneity from an frk-recombinant Z. mobilis strain showing a specific activity of 205 +/- 25 U of protein mg-1 with fructose (K(m), 0.75 +/- 0.06 mM) and 17 +/- 2 U mg-1 (relative activity, 8.5%) with mannose (K(m), 0.65 +/- 0.08 mM). However, no phosphomannoseisomerase activity could be detected for Z. mobilis, and this appeared to be the reason for the lack of growth on mannose. Therefore, we introduced the Escherichia coli gene pmi (manA) in Z. mobilis under the control of a lacIq-Ptac system on a broad-host-range plasmid (pZY507; Cmr). Subsequently, in pmi-recombinant cells of Z. mobilis, phosphomannoseisomerase was expressed in a range of from 3 U (without isopropyl-beta-D-thiogalactopyranoside [IPTG]) to 20 U mg-1 of protein in crude extracts (after IPTG induction). Recombinant cells of different Z. mobilis strains utilized mannose (4%) as the sole carbon source with a growth rate of 0.07 h-1, provided that they contained fructokinase activity. When the frk gene was additionally expressed from the same vector, fructokinase activities of as much as 9.7 U mg-1 and growth rates of as much as 0.25 h-1 were detected, compared with 0.34 h-1 on fructose for wild-type Z. mobilis. Selection for growth on mannose was used to monitor plasmid transfer of pZY507pmi from E. coli to Z. mobilis strains and could replace the previous selection for antibiotic resistance.
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Affiliation(s)
- P Weisser
- Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, Germany
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Weisser P, Krämer R, Sahm H, Sprenger GA. Functional expression of the glucose transporter of Zymomonas mobilis leads to restoration of glucose and fructose uptake in Escherichia coli mutants and provides evidence for its facilitator action. J Bacteriol 1995; 177:3351-4. [PMID: 7768841 PMCID: PMC177034 DOI: 10.1128/jb.177.11.3351-3354.1995] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The Zymomonas mobilis genes encoding the glucose facilitator (glf), glucokinase (glk), or fructokinase (frk) were cloned and expressed in a lacIq-Ptac system using Escherichia coli K-12 mutants deficient in uptake and phosphorylation of glucose and fructose. Growth on glucose or fructose was restored when the respective genes (glf-glk or glf-frk) were expressed. In E. coli glf+ strains, both glucose and fructose were taken up via facilitated diffusion (Km, 4.1 mM for glucose and 39 mM for fructose; Vmax at 15 degrees C, 75 and 93 nmol min-1 mg-1 [dry weight] for glucose and fructose, respectively). For both substrates, counterflow maxima were observed.
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Affiliation(s)
- P Weisser
- Institut für Biotechnologie, Forschungszentrum Jülich GmbH, Germany
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Parker C, Barnell WO, Snoep JL, Ingram LO, Conway T. Characterization of the Zymomonas mobilis glucose facilitator gene product (glf) in recombinant Escherichia coli: examination of transport mechanism, kinetics and the role of glucokinase in glucose transport. Mol Microbiol 1995; 15:795-802. [PMID: 7596282 DOI: 10.1111/j.1365-2958.1995.tb02350.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Zymomonas mobilis is known to transport glucose by a facilitated diffusion process. A putative glucose facilitator gene (glf), closely related to a large family of glucose transporters, is located in a cluster of genes that code for enzymes of glucose metabolism. The Z. mobilis glf gene is able to complement glucose transport in an Escherichia coli strain that is defective in native glucose transport and glucokinase. In this study, the recombinant E. coli was shown to be capable of influx counterflow when preloaded with glucose and had an apparent Km for glucose of approximately 1.1-2.9 mM, consistent with the function of Glf as a low-affinity glucose facilitator. The ability of glucokinase mutants expressing glf to transport glucose made it clear that glucokinase activity was not required for Glf-dependent glucose transport. The possibility that glucokinase can interact with Glf to improve the affinity for glucose was not supported since expression of the Z. mobilis glucokinase gene, in addition to glf, did not affect the Km of Glf for glucose in recombinant E. coli. The inability of various sugars to compete with glucose during glucose transport by recombinant E. coli expressing glf indicated that Glf is specific for glucose. While the results of fructose transport assays did not completely rule out the possibility of very low affinity for fructose, the apparent specificity of Glf for glucose makes it possible that Z. mobilis utilizes a different transporter(s) for fructose.
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Affiliation(s)
- C Parker
- School of Biological Sciences, University of Nebraska, Lincoln 68588-0118, USA
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