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Mukherjee T, Venkata Mohan S. Metabolic flux of Bacillus subtilis under poised potential in electrofermentation system: Gene expression vs product formation. BIORESOURCE TECHNOLOGY 2021; 342:125854. [PMID: 34537531 DOI: 10.1016/j.biortech.2021.125854] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Revised: 08/23/2021] [Accepted: 08/25/2021] [Indexed: 06/13/2023]
Abstract
The role of poised (negative/positive) potential (0.2/0.4/0.6/0.8 V vs Ag/AgCl at anode) was studied in electrofermentation system (EF) to understand the metabolic flux of Bacillus subtilis with pyruvate as a carbon source. The relative expression of genes encoding pyruvate dehydrogenase (pdhA), lactate dehydrogenase (lctE), acetate kinase (ackA), pyruvate carboxylase (pycA), adenylosuccinate lyase (purB), acylCoA dehydrogenase (acdA) and NADH dehydrogenase (ndh) allowed evaluation of metabolic changes in correlation to product formation and bioelectrochemical analysis. In comparison to control, poised circumstances showed marked influence on product profile with up-regulation of key enzymes involved in pyruvate metabolism. EF poised with - 0.8 V and -0.6 V enhanced bio-hydrogen production by 6 folds and 4 folds respectively. Concomitantly, -0.8 V resulted in maximum ethanol and acetic acid production whilst, -0.6 V and + 0.6 V resulted in maximum lactic acid and succinic acid production respectively. The transcripts for genes associated synthesis were upregulated in the respected poised reactors.
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Affiliation(s)
- Triya Mukherjee
- Bioengineering and Environmental Sciences Lab, Department of Energy and Environmental Engineering, CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 007, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - S Venkata Mohan
- Bioengineering and Environmental Sciences Lab, Department of Energy and Environmental Engineering, CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 007, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
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Strengthening the (R)-pantoate pathway to produce D-pantothenic acid based on systematic metabolic analysis. FOOD BIOSCI 2021. [DOI: 10.1016/j.fbio.2021.101283] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Integrated analysis of gene expression and metabolic fluxes in PHA-producing Pseudomonas putida grown on glycerol. Microb Cell Fact 2016; 15:73. [PMID: 27142075 PMCID: PMC4855977 DOI: 10.1186/s12934-016-0470-2] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Accepted: 04/24/2016] [Indexed: 02/02/2023] Open
Abstract
Background Given its high surplus and low cost, glycerol has emerged as interesting carbon substrate for the synthesis of value-added chemicals. The soil bacterium Pseudomonas putida KT2440 can use glycerol to synthesize medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA), a class of biopolymers of industrial interest. Here, glycerol metabolism in P. putida KT2440 was studied on the level of gene expression (transcriptome) and metabolic fluxes (fluxome), using precisely adjusted chemostat cultures, growth kinetics and stoichiometry, to gain a systematic understanding of the underlying metabolic and regulatory network. Results Glycerol-grown P. putida KT2440 has a maintenance energy requirement [0.039 (mmolglycerol (gCDW h)−1)] that is about sixteen times lower than that of other bacteria, such as Escherichia coli, which provides a great advantage to use this substrate commercially. The shift from carbon (glycerol) to nitrogen (ammonium) limitation drives the modulation of specific genes involved in glycerol metabolism, transport electron chain, sensors to assess the energy level of the cell, and PHA synthesis, as well as changes in flux distribution to increase the precursor availability for PHA synthesis (Entner–Doudoroff pathway and pyruvate metabolism) and to reduce respiration (glyoxylate shunt). Under PHA-producing conditions (N-limitation), a higher PHA yield was achieved at low dilution rate (29.7 wt% of CDW) as compared to a high rate (12.8 wt% of CDW). By-product formation (succinate, malate) was specifically modulated under these regimes. On top of experimental data, elementary flux mode analysis revealed the metabolic potential of P. putida KT2440 to synthesize PHA and identified metabolic engineering targets towards improved production performance on glycerol. Conclusion This study revealed the complex interplay of gene expression levels and metabolic fluxes under PHA- and non-PHA producing conditions using the attractive raw material glycerol as carbon substrate. This knowledge will form the basis for the development of future metabolically engineered hyper-PHA-producing strains derived from the versatile bacterium P. putida KT2440.
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Vivijs B, Moons P, Aertsen A, Michiels CW. Acetoin synthesis acquisition favors Escherichia coli growth at low pH. Appl Environ Microbiol 2014; 80:6054-61. [PMID: 25063653 PMCID: PMC4178668 DOI: 10.1128/aem.01711-14] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Accepted: 07/17/2014] [Indexed: 11/20/2022] Open
Abstract
Some members of the family Enterobacteriaceae ferment sugars via the mixed-acid fermentation pathway. This yields large amounts of acids, causing strong and sometimes even lethal acidification of the environment. Other family members employ the 2,3-butanediol fermentation pathway, which generates comparatively less acidic and more neutral end products, such as acetoin and 2,3-butanediol. In this work, we equipped Escherichia coli MG1655 with the budAB operon, encoding the acetoin pathway, from Serratia plymuthica RVH1 and investigated how this affected the ability of E. coli to cope with acid stress during growth. Acetoin fermentation prevented lethal medium acidification by E. coli in lysogeny broth (LB) supplemented with glucose. It also supported growth and higher stationary-phase cell densities in acidified LB broth with glucose (pH 4.10 to 4.50) and in tomato juice (pH 4.40 to 5.00) and reduced the minimal pH at which growth could be initiated. On the other hand, the acetoin-producing strain was outcompeted by the nonproducer in a mixed-culture experiment at low pH, suggesting a fitness cost associated with acetoin production. Finally, we showed that acetoin production profoundly changes the appearance of E. coli on several diagnostic culture media. Natural E. coli strains that have laterally acquired budAB genes may therefore have escaped detection thus far. This study demonstrates the potential importance of acetoin fermentation in the ecology of E. coli in the food chain and contributes to a better understanding of the microbiological stability and safety of acidic foods.
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Affiliation(s)
- Bram Vivijs
- Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (MS), Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Pieter Moons
- Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (MS), Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Abram Aertsen
- Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (MS), Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Chris W Michiels
- Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (MS), Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Leuven, Belgium
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Manipulation of the anoxic metabolism in Escherichia coli by ArcB deletion variants in the ArcBA two-component system. Appl Environ Microbiol 2012; 78:8784-94. [PMID: 23064346 DOI: 10.1128/aem.02558-12] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Bioprocesses conducted under conditions with restricted O(2) supply are increasingly exploited for the synthesis of reduced biochemicals using different biocatalysts. The model facultative anaerobe Escherichia coli has elaborate sensing and signal transduction mechanisms for redox control in response to the availability of O(2) and other electron acceptors. The ArcBA two-component system consists of ArcB, a membrane-associated sensor kinase, and ArcA, the cognate response regulator. The tripartite hybrid kinase ArcB possesses a transmembrane, a PAS, a primary transmitter (H1), a receiver (D1), and a phosphotransfer (H2) domain. Metabolic fluxes were compared under anoxic conditions in a wild-type E. coli strain, its ΔarcB derivative, and two partial arcB deletion mutants in which ArcB lacked either the H1 domain or the PAS-H1-D1 domains. These analyses revealed that elimination of different segments in ArcB determines a distinctive distribution of d-glucose catabolic fluxes, different from that observed in the ΔarcB background. Metabolite profiles, enzyme activity levels, and gene expression patterns were also investigated in these strains. Relevant alterations were observed at the P-enol-pyruvate/pyruvate and acetyl coenzyme A metabolic nodes, and the formation of reduced fermentation metabolites, such as succinate, d-lactate, and ethanol, was favored in the mutant strains to different extents compared to the wild-type strain. These phenotypic traits were associated with altered levels of the enzymatic activities operating at these nodes, as well as with elevated NADH/NAD(+) ratios. Thus, targeted modification of global regulators to obtain different metabolic flux distributions under anoxic conditions is emerging as an attractive tool for metabolic engineering purposes.
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De Mey M, Lequeux GJ, Beauprez JJ, Maertens J, Waegeman HJ, Van Bogaert IN, Foulquié-Moreno MR, Charlier D, Soetaert WK, Vanrolleghem PA, Vandamme EJ. Transient metabolic modeling of Escherichia coli MG1655 and MG1655 DeltaackA-pta, DeltapoxB Deltapppc ppc-p37 for recombinant beta-galactosidase production. J Ind Microbiol Biotechnol 2010; 37:793-803. [PMID: 20440535 DOI: 10.1007/s10295-010-0724-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Accepted: 04/10/2010] [Indexed: 10/19/2022]
Abstract
Escherichia coli is one of the most widely used hosts for the production of recombinant proteins, among other reasons because its genetics are far better characterized than those of any other microorganism. To improve the understanding of recombinant protein synthesis in E. coli, the production of a model recombinant protein, beta-galactosidase, was studied in response to the constitutive overexpression of the anaplerotic reaction afforded by PEP carboxylase. To this end, an IPTG wash-in experiment was performed starting from a well-defined steady-state condition for both the wild-type E. coli and a mutant with a defective acetate pathway and a constitutively overexpressed ppc. In order to compare the dynamics of the fluxes over time during the wash-in experiment, a method referred to as transient metabolic flux analysis, which is based on steady-state metabolic flux analysis, was used. This allowed us to track the intracellular changes/fluxes in both strains. It was observed that the flux towards fermentation products was 3.6 times lower in the ppc overexpression mutant compared to the wild-type E. coli. In the former on the other hand, the PPC flux is in general higher. In addition, the flux towards beta-galactosidase was higher (12.4 times), resulting in five times more protein activity. These results indicate that by constitutively overexpressing the anaplerotic ppc gene in E. coli, the TCA cycle intermediates are increasingly replenished. The additional supply of these protein precursors has a positive result on recombinant protein production.
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Affiliation(s)
- Marjan De Mey
- Laboratory of Industrial Microbiology and Biocatalysis, Department of Biochemical and Microbial Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
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Kim TY, Kim HU, Park JM, Song H, Kim JS, Lee SY. Genome-scale analysis of Mannheimia succiniciproducens metabolism. Biotechnol Bioeng 2007; 97:657-71. [PMID: 17405177 DOI: 10.1002/bit.21433] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Mannheimia succiniciproducens MBEL55E isolated from bovine rumen is a capnophilic gram-negative bacterium that efficiently produces succinic acid, an industrially important four carbon dicarboxylic acid. In order to design a metabolically engineered strain which is capable of producing succinic acid with high yield and productivity, it is essential to optimize the whole metabolism at the systems level. Consequently, in silico modeling and simulation of the genome-scale metabolic network was employed for genome-scale analysis and efficient design of metabolic engineering experiments. The genome-scale metabolic network of M. succiniciproducens consisting of 686 reactions and 519 metabolites was constructed based on reannotation and validation experiments. With the reconstructed model, the network structure and key metabolic characteristics allowing highly efficient production of succinic acid were deciphered; these include strong PEP carboxylation, branched TCA cycle, relative weak pyruvate formation, the lack of glyoxylate shunt, and non-PTS for glucose uptake. Constraints-based flux analyses were then carried out under various environmental and genetic conditions to validate the genome-scale metabolic model and to decipher the altered metabolic characteristics. Predictions based on constraints-based flux analysis were mostly in excellent agreement with the experimental data. In silico knockout studies allowed prediction of new metabolic engineering strategies for the enhanced production of succinic acid. This genome-scale in silico model can serve as a platform for the systematic prediction of physiological responses of M. succiniciproducens to various environmental and genetic perturbations and consequently for designing rational strategies for strain improvement.
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Affiliation(s)
- Tae Yong Kim
- Department of Chemical and Biomolecular Engineering (BK21 Program), Metabolic and Biomolecular Engineering National Research Laboratory, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
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Wlaschin AP, Trinh CT, Carlson R, Srienc F. The fractional contributions of elementary modes to the metabolism of Escherichia coli and their estimation from reaction entropies. Metab Eng 2006; 8:338-52. [PMID: 16581276 DOI: 10.1016/j.ymben.2006.01.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 01/04/2006] [Accepted: 01/31/2006] [Indexed: 11/21/2022]
Abstract
The metabolism of a cell can be viewed as a weighted sum of elementary modes. Due to the multiplicity of modes the identification of the individual weights represents a non-trivial problem. To enable the determination of weighting factors we have identified and implemented two gene deletions in combination with defined growth conditions that limit the metabolism from 4374 original elementary modes to 24 elementary modes for a non-PHB synthesizing control and 40 modes for a PHB synthesizing strain. These remaining modes can be further grouped into five families that have the same overall stoichiometry. Thus, the complexity of the problem is significantly reduced, and weighting factors for each family of modes could be determined from the measurement of accumulation rates of metabolites. Moreover, it is shown that individual weights are inversely correlated with the entropy generated by the operation of the used pathways defined in elementary modes. This suggests that evolution developed cellular regulatory patterns that permit diversity of pathways while favoring efficient pathways with low entropy generation. Furthermore, such correlation provides a rational way of estimating metabolic fluxes based on the thermodynamic properties of elementary modes. This is demonstrated with an example in which experimentally determined, intracellular fluxes are shown to be highly correlated with fluxes computed based on elementary modes and reaction entropies. The analysis suggests that the set of elementary modes can be interpreted analogous to a metabolic ensemble of quantum states of a macroscopic system.
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Affiliation(s)
- Aaron P Wlaschin
- 240 Gortner Laboratory, Department of Chemical Engineering and Materials Science, and BioTechnology Institute, University of Minnesota, 1479 Gortner Avenue, St. Paul, MN 55455/55108, USA
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Li XJ, Chen T, Chen X, Zhao XM. Redirection electron flow to high coupling efficiency of terminal oxidase to enhance riboflavin biosynthesis. Appl Microbiol Biotechnol 2006; 73:374-83. [PMID: 16736087 DOI: 10.1007/s00253-006-0482-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2005] [Revised: 04/19/2006] [Accepted: 04/21/2006] [Indexed: 10/24/2022]
Abstract
The metabolic impact of redirection electron flow to high coupling efficiency of terminal oxidases on riboflavin biosynthetic ability was quantitatively assessed during batch culture in this paper. While disruption of the low coupling bd oxidase of the riboflavin overproducing B. subtilis PK, the apparent phenotype with more rapid specific growth rate and higher biomass yield was achieved. Compared to by-products formation, a discernible shift to less acetate and more acetoin in cyd mutant was observed. As the overflow metabolism was decreased in B. subtilis PK cyd, more carbon source was directed to biomass and riboflavin biosynthetic pathway, which resulted in higher biomass and about 30% improvement of riboflavin biosynthetic ability. The higher product-corrected biomass yield in mutant showed that the efficient energy generation is an important factor for exponential growth of riboflavin overproducing B. subtilis strain in batch culture.
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Affiliation(s)
- Xiao-Jing Li
- School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
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Bühler B, Straathof AJJ, Witholt B, Schmid A. Analysis of Two-Liquid-Phase Multistep Biooxidation Based on a Process Model: Indications for Biological Energy Shortage. Org Process Res Dev 2006. [DOI: 10.1021/op060028g] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Bruno Bühler
- Chair of Chemical Biotechnology, University of Dortmund, D-44221 Dortmund, Germany, Department of Biotechnology, Delft University of Technology, Julianalaan 67, NL-2628 BC Delft, The Netherlands, and Institute of Biotechnology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Adrie J. J. Straathof
- Chair of Chemical Biotechnology, University of Dortmund, D-44221 Dortmund, Germany, Department of Biotechnology, Delft University of Technology, Julianalaan 67, NL-2628 BC Delft, The Netherlands, and Institute of Biotechnology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Bernard Witholt
- Chair of Chemical Biotechnology, University of Dortmund, D-44221 Dortmund, Germany, Department of Biotechnology, Delft University of Technology, Julianalaan 67, NL-2628 BC Delft, The Netherlands, and Institute of Biotechnology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Andreas Schmid
- Chair of Chemical Biotechnology, University of Dortmund, D-44221 Dortmund, Germany, Department of Biotechnology, Delft University of Technology, Julianalaan 67, NL-2628 BC Delft, The Netherlands, and Institute of Biotechnology, ETH Zurich, CH-8093 Zurich, Switzerland
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Sánchez AM, Bennett GN, San KY. Batch culture characterization and metabolic flux analysis of succinate-producing Escherichia coli strains. Metab Eng 2006; 8:209-26. [PMID: 16434224 DOI: 10.1016/j.ymben.2005.11.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Revised: 11/15/2005] [Accepted: 11/22/2005] [Indexed: 11/28/2022]
Abstract
This study presents an in-depth analysis of the anaerobic metabolic fluxes of various mutant strains of Escherichia coli overexpressing the Lactococcus lactis pyruvate carboxylase (PYC) for the production of succinate. Previously, a metabolic network design that includes an active glyoxylate pathway implemented in vivo increased succinate yield from glucose in an E. coli mutant to 1.6 mol/mol under fully anaerobic conditions. The design consists of a dual succinate synthesis route, which diverts required quantities of NADH through the traditional fermentative pathway and maximizes the carbon converted to succinate by balancing the carbon flux through the fermentative pathway and the glyoxylate pathway (which has a lower NADH requirement). Mutant strains previously constructed during the development of high-yield succinate-producing strains were selected for further characterization to understand their metabolic response as a result of several genetic manipulations and to determine the significance of the fermentative and the glyoxylate pathways in the production of succinate. Measured fluxes obtained under batch cultivation conditions were used to estimate intracellular fluxes and identify critical branch point flux split ratios. The comparison of changes in branch point flux split ratios to the glyoxylate pathway and the fermentative pathway at the oxaloacetate (OAA) node as a result of different mutations revealed the sensitivity of succinate yield to these manipulations. The most favorable split ratio to obtain the highest succinate yield was the fractional partition of OAA to glyoxylate of 0.32 and 0.68 to the fermentative pathway obtained in strains SBS550MG (pHL413) and SBS990MG (pHL413). The succinate yields achieved in these two strains were 1.6 and 1.7 mol/mol, respectively. In addition, an active glyoxylate pathway in an ldhA, adhE, ack-pta mutant strain is shown to be responsible for the high succinate yields achieved anaerobically. Furthermore, in vitro activity measurements of seven crucial enzymes involved in the pathways studied and intracellular measurements of key intermediate metabolite pools provided additional insights on the physiological perturbations caused by these mutations. The characterization of these recombinant mutant strains in terms of flux distribution pattern, in vitro enzyme activity and intracellular metabolite pools provides useful information for the rational modification of metabolic fluxes to improve succinate production.
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Affiliation(s)
- Ailen M Sánchez
- Department of Bioengineering, Rice University, Houston, TX, USA
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Levanon SS, San KY, Bennett GN. Effect of oxygen on the Escherichia coli ArcA and FNR regulation systems and metabolic responses. Biotechnol Bioeng 2005; 89:556-64. [PMID: 15669087 DOI: 10.1002/bit.20381] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Escherichia coli has several elaborate sensing mechanisms for response to the availability of oxygen and the presence of other electron acceptors. The adaptive responses are coordinated by a group of global regulators, which include the one-component Fnr protein, and the two-component Arc system. To quantitate the contribution of Arc and Fnr-dependent regulation in catabolism, arcA and fnr mutant strains were constructed using the recently developed lambda derived recombination system. The metabolic activity of wildtype E. coli, an arcA mutant, an fnr mutant, and a double arcA-fnr mutant, via the fermentative pathways in glucose-limited cultures and different oxygen concentrations was studied in chemostat cultures at steady state. It was found that the most significant role of ArcA is under microaerobic conditions, while that of FNR is under more strictly anaerobic conditions. The FNR protein is normally inactive during microaerobic conditions. However, our results indicate that in the arcA mutant strain the cells behave as if a higher level of the FNR regulator is in the activated form compared to the wildtype strain during the transition from aerobic to microanaerobic growth. The results show a significant increase in the flux through pyruvate formate lyase (PFL) in the presence of oxygen. The activity of FNR-regulated pathways in the arcA mutant strain is correlated with the high redox potential obtained under microaerobic growth.
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Affiliation(s)
- Sagit Shalel Levanon
- Department of Biochemistry and Cell Biology, MS 140, 6100 Main St., Rice University, Houston, TX 77005-1892, USA
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Sánchez AM, Bennett GN, San KY. Effect of different levels of NADH availability on metabolic fluxes of Escherichia coli chemostat cultures in defined medium. J Biotechnol 2005; 117:395-405. [PMID: 15925720 DOI: 10.1016/j.jbiotec.2005.02.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2004] [Revised: 02/07/2005] [Accepted: 02/21/2005] [Indexed: 10/25/2022]
Abstract
Escherichia coli overexpressing a NAD(+)-dependent formate dehydrogenase (FDH) from Candida boidinii was grown in chemostat culture on various carbon sources at 0.05 h(-1) dilution rate, under anaerobic conditions using defined medium and compared to a control without the heterologous FDH pathway. Metabolic fluxes, NADH/NAD(+) ratios and NAD(H/(+)) levels were determined under a range of intracellular NADH availability. The effect of NADH manipulation on the distribution of metabolic fluxes in E. coli was assessed under steady-state conditions. The heterologous FDH pathway converts 1 mol of formate into 1 mol of NADH and carbon dioxide, in contrast with the native FDH where no cofactor involvement is present. Previously, we found that this NADH regeneration system doubled the maximum yield of NADH from 2 to 4 mol NADH/mol glucose consumed and reached 4.6 mol NADH/mol of substrate when sorbitol was used as a carbon source in a complex medium. In the current study, it was found that higher NADH yields and NADH/NAD(+) ratios were achieved with our in vivo NADH regeneration system compared to a control lacking the new FDH pathway in the three carbon sources (glucose, gluconate and sorbitol) examined suggesting a more reduced intracellular environment. The total NAD(H/(+)) amounts were very similar for all the combinations studied. It was also found that the ethanol to acetate ratio increased with increased NADH availability. This ratio increased from 1.05 for the control strain in glucose to 9.45 for the strain expressing the heterologous NAD(+)-dependent FDH in sorbitol.
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Affiliation(s)
- Ailen M Sánchez
- Department of Bioengineering, Rice University, 6100 Main Street, MS-142, Houston, TX, USA
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Vemuri GN, Minning TA, Altman E, Eiteman MA. Physiological response of central metabolism inEscherichia coli to deletion of pyruvate oxidase and introduction of heterologous pyruvate carboxylase. Biotechnol Bioeng 2005; 90:64-76. [PMID: 15736164 DOI: 10.1002/bit.20418] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We studied the physiological response of Escherichia coli central metabolism to the expression of heterologous pyruvate carboxylase (PYC) in the presence and absence of pyruvate oxidase (POX). These studies were complemented with expression analysis of central and intermediary metabolic genes and conventional in vitro enzyme assays to evaluate glucose metabolism at steady-state growth conditions (chemostats). The absence of POX activity reduced nongrowth-related energy metabolism (maintenance coefficient) and increased the maximum specific rate of oxygen consumption. The presence of PYC activity (i.e., with POX activity) increased the biomass yield coefficient and reduced the maximum specific oxygen consumption rate compared to the wildtype. The presence of PYC in a poxB mutant resulted in a 42% lower maintenance coefficient and a 42% greater biomass yield compared to the wildtype. Providing E. coli with PYC or removing POX increased the threshold specific growth rate at which acetate accumulation began, with an 80% reduction in acetate accumulation observed at a specific growth rate of 0.4 h-1 in the poxB-pyc+ strain. Gene expression analysis suggests utilization of energetically less favorable glucose metabolism via glucokinase and the Entner-Doudoroff pathway in the absence of functional POX, while the upregulation of the phosphotransferase glucose uptake system and several amino acid biosynthetic pathways occurs in the presence of PYC. The physiological and expression changes resulting from these genetic perturbations demonstrate the importance of the pyruvate node in respiration and its impact on acetate overflow during aerobic growth.
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Affiliation(s)
- G N Vemuri
- Center for Molecular BioEngineering, Driftmier Engineering, University of Georgia, Athens, Georgia 30602, USA
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San KY, Bennett GN, Berríos-Rivera SJ, Vadali RV, Yang YT, Horton E, Rudolph FB, Sariyar B, Blackwood K. Metabolic engineering through cofactor manipulation and its effects on metabolic flux redistribution in Escherichia coli. Metab Eng 2002; 4:182-92. [PMID: 12009797 DOI: 10.1006/mben.2001.0220] [Citation(s) in RCA: 193] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Applications of genetic engineering or metabolic engineering have increased in both academic and industrial institutions. Most current metabolic engineering studies have focused on enzyme levels and on the effect of the amplification, addition, or deletion of a particular pathway. Although it is generally known that cofactors play a major role in the production of different fermentation products, their role has not been thoroughly and systematically studied. It is conceivable that in cofactor-dependent production systems, cofactor availability and the proportion of cofactor in the active form may play an important role in dictating the overall process yield. Hence, the manipulation of these cofactor levels may be crucial in order to further increase production. We have demonstrated that manipulation of cofactors can be achieved by external and genetic means and these manipulations have the potential to be used as an additional tool to achieve desired metabolic goals. We have shown experimentally that the NADH/NAD(+) ratio can be altered by using carbon sources with different oxidation states. We have shown further that the metabolite distribution can be influenced by a change in the NADH/NAD(+) ratio as mediated by the oxidation state of the carbon source used. We have also demonstrated that the total NAD(H/(+)) levels can be increased by the overexpression of the pncB gene. The increase in the total NAD(H/(+)) levels can be achieved even in a complex medium, which is commonly used by most industrial processes. Finally, we have shown that manipulation of the CoA pool/flux can be used to increase the productivity of a model product, isoamyl acetate.
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Affiliation(s)
- Ka-Yiu San
- Department of Bioengineering, Institute of Biosciences and Bioengineering, Rice University, Houston, Texas 77005, USA
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Phelps TJ, Palumbo AV, Beliaev AS. Metabolomics and microarrays for improved understanding of phenotypic characteristics controlled by both genomics and environmental constraints. Curr Opin Biotechnol 2002; 13:20-4. [PMID: 11849953 DOI: 10.1016/s0958-1669(02)00279-3] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Advances in our understanding of functional genomics are best addressed by integrative studies that include measurements of mRNA, proteins, and low molecular weight metabolites over time and varied conditions. Bioinformatics can then be used to relate this data to the genome. Current technology allows for comprehensive and rapid mRNA expression profiling and mass spectrophotometric measurement of low molecular weight intermediates and metabolic products. In prokaryotic organisms, this combination provides a potentially powerful tool for identifying gene function and regulatory networks even in the absence of a combined proteomic approach.
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Affiliation(s)
- Tommy J Phelps
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6038, USA.
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Yanagimachi KS, Stafford DE, Dexter AF, Sinskey AJ, Drew S, Stephanopoulos G. Application of radiolabeled tracers to biocatalytic flux analysis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:4950-60. [PMID: 11559364 DOI: 10.1046/j.0014-2956.2001.02426.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Radiolabeled tracers can provide valuable information about the structure of and flux distributions in biocatalytic reaction networks. This method derives from prior studies of glucose metabolism in mammalian systems and is implemented by pulsing a culture with a radiolabeled metabolite that can be transported into the cells and subsequently measuring the radioactivity of all network metabolites following separation by liquid chromatography. Intracellular fluxes can be directly determined from the transient radioactivity count data by tracking the depletion of the radiolabeled metabolite and/or the accompanying accumulation of any products formed. This technique differs from previous methods in that it is applied within a systems approach to the problem of flux determination. It has been used for the investigation of the indene bioconversion network expressed in Rhodococcus sp. KY1. Flux estimates obtained by radioactive tracers were confirmed by macroscopic metabolite balancing and showed that indene oxidation in steady state chemostat cultures proceeds primarily through a monooxygenase activity forming (1S,2R)-indan oxide, with no dehydrogenation of trans-(1R,2R)-indandiol. These results confirmed the significance of indan oxide formation and identified the hydrolysis of indan oxide as a key step in maximizing the production of (2R)-indandiol, a chiral precursor of the HIV protease inhibitor, Crixivan.
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Affiliation(s)
- K S Yanagimachi
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 02139, USA
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Çalık P, Çalık G, Özdamar TH. BIOPROCESS DEVELOPMENT FOR SERINE ALKALINE PROTEASE PRODUCTION: A REVIEW. REV CHEM ENG 2001. [DOI: 10.1515/revce.2001.17.s1.1] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Energetics and carbon metabolism during growth of microalgal cells under photoautotrophic, mixotrophic and cyclic light-autotrophic/dark-heterotrophic conditions. Biochem Eng J 2000; 6:87-102. [PMID: 10959082 DOI: 10.1016/s1369-703x(00)00080-2] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Chlorella pyrenoidosa was cultivated under photoautotrophic, mixotrophic and cyclic light-autotrophic/dark-heterotrophic conditions. The influence of light on the carbon and energy metabolism of microalgae was investigated by the use of metabolic flux analysis. The respiratory activity of microalgae in the light was assessed from the autotrophic flux distribution. Results showed that the glycolytic pathway, tricarboxylic acid cycle and mitochondrial oxidative phosphorylation maintained high activities during illumination, indicating little effect of light on these pathways, while the flux through the pentose phosphate pathway during illumination was very small due to the light-mediated regulation. The theoretical yields of biomass on ATP decreased in the following order: heterotrophic culture>mixotrophic culture>autotrophic culture, and a significant amount of the available ATP was required for maintenance processes in microalgal cells. The energy conversion efficiency between the supplied energy to culture, the absorbed energy by cells and the free energy conserved in ATP were analyzed for the different cultures. Analysis showed that the heterotrophic culture generated more ATP from the supplied energy than the autotrophic and mixotrophic cultures. The maximum thermodynamic efficiency of ATP production from the absorbed energy, which was calculated from the metabolic fluxes at zero growth rate, was the highest in the heterotrophic culture and as low as 16% in the autotrophic culture. By evaluating the energy economy through the energy utilization efficiency, it was found that the biomass yield on the supplied energy was the lowest in the autotrophic cultivation, and the cyclic culture gave the most efficient utilization of energy for biomass production.
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Yang YT, Peredelchuk M, Bennett GN, San KY. Effect of variation of Klebsiella pneumoniae acetolactate synthase expression on metabolic flux redistribution in Escherichia coli. Biotechnol Bioeng 2000; 69:150-9. [PMID: 10861394 DOI: 10.1002/(sici)1097-0290(20000720)69:2<150::aid-bit4>3.0.co;2-n] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Escherichia coli strains carrying the Bacillus subtilis acetolactate synthase (ALS) gene were previously shown to produce less acetate with higher ATP yields. Metabolic flux analysis was used to show that excess pyruvate was channeled into the less inhibitory product, acetoin. To further understand the role of intrinsic enzymatic properties and the effect of variations in enzyme levels in the alternation of metabolic fluxes, we constructed a chromosomal integrant of the Klebsiella pneumoniae ALS gene. The reported in vitro Michaelis-Menten constants (K(m)) for the Bacillus and the Klebsiella ALS are 13.0 mM and 8.0 mM, respectively. Furthermore, expression of the Klebsiella ALS is under the control of an inducible trp promoter system. Shake-flask experiments showed a linear induction response (the ALS activity changes from about 9 to 223 U/mg of protein when the inducer concentration [IAA] varied from 0 to 40 mg/L). Chemostat experiments showed a similar induction response. Interactions between the branched reactions catalyzed by the PFL, LDH, and the ALS enzymes at the pyruvate node were examined. The results indicate the importance of in vivo enzyme activities in the redistribution of metabolic fluxes.
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Affiliation(s)
- Y T Yang
- Departments of Bioengineering and Chemical Engineering Institute of Biosciences and Bioengineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
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Abstract
Mathematical models of the cellular metabolism have a special interest within biotechnology. Many different kinds of commercially important products are derived from the cell factory, and metabolic engineering can be applied to improve existing production processes, as well as to make new processes available. Both stoichiometric and kinetic models have been used to investigate the metabolism, which has resulted in defining the optimal fermentation conditions, as well as in directing the genetic changes to be introduced in order to obtain a good producer strain or cell line. With the increasing availability of genomic information and powerful analytical techniques, mathematical models also serve as a tool for understanding the cellular metabolism and physiology.
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Affiliation(s)
- A K Gombert
- Department of Chemical Engineering, CP 61548, University of São Paulo, São Paulo, 05424-970, Brazil.
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