Metabolic Engineering Applications Research Articles

Optimization of the dynamic regulation in a branch-in metabolic pathway

Multiobjective optimization has already been shown to be an appropriate tool to characterize and tune systems subject to multiple trade-offs among competing objectives. Here, we consider the dynamic regulation of a merging metabolic pathway motif. This motif appears in a wide range of metabolic engineering applications, including the production of phenylpropanoids highly appreciated by the pharma, nutraceutical and the cosmetic industries. We present an approach to use multiobjective optimization for the optimal tuning of the gene circuit parts composing the biomolecular controller and biosensor in the dynamic regulation of the metabolic pathway. We show how this approach can deal with the trade-offs between performance of the regulated pathway, robustness with respect to perturbations, and stability of the feedback loop. Our results suggest that the strategies for fine-tuning the tradeoffs among performance, robustness, and stability in dynamic pathway regulation are complex and it is not always possible to infer them by simple inspection. This renders the use of the multiobjective optimization methodology not only useful but necessary.

Actinobacteria challenge the paradigm: A unique protein architecture for a well-known, central metabolic complex

α-oxoacid dehydrogenase complexes are large, tripartite enzymatic machineries carrying out key reactions in central metabolism. Extremely conserved across the tree of life, they have been, so far, all considered to be structured around a high-molecular weight hollow core, consisting of up to 60 subunits of the acyltransferase component. We provide here evidence that Actinobacteria break the rule by possessing an acetyltranferase component reduced to its minimally active, trimeric unit, characterized by a unique C-terminal helix bearing an actinobacterial specific insertion that precludes larger protein oligomerization. This particular feature, together with the presence of an odhA gene coding for both the decarboxylase and the acyltransferase domains on the same polypetide, is spread over Actinobacteria and reflects the association of PDH and ODH into a single physical complex. Considering the central role of the pyruvate and 2-oxoglutarate nodes in central metabolism, our findings pave the way to both therapeutic and metabolic engineering applications.

A High-Throughput HILIC-MS-Based Metabolomic Assay for the Analysis of Polar Metabolites.

Mass spectrometry (MS)-based metabolomics approaches have been used for characterizing the metabolite content and composition of biological samples in drug discovery and development, as well as in metabolic engineering, and food and plant sciences applications. Here, we describe a protocol routinely used in our laboratory to conduct a metabolic profiling of small polar metabolites from biological samples. Metabolites can be extracted from each sample using a methanol-based single-phase extraction procedure. The combination of LC-based hydrophilic interaction liquid chromatography (HILIC) and a hybrid quadrupole-time of flight (Q-ToF) mass spectrometer allows the comprehensive analysis of small polar metabolites including sugars, phosphorylated compounds, purines and pyrimidines, nucleotides, nucleosides, acylcarnitines, carboxylic acids, hydrophilic vitamins and amino acids. Retention times and accurate masses of metabolites involved in key metabolic pathways are annotated for routine high-throughput screening in both untargeted and targeted metabolomics analyses.

Methods for the Development of Recombinant Microorganisms for the Production of Natural Products.

Metabolic engineering strives to develop microbial strains that are capable of producing a target chemical in a biological organism. There are still many challenges to overcome in order to achieve titers, yields, and productivities necessary for industrial production. The use of recombinant microorganisms to meet these needs is the next step for metabolic engineers. In this chapter, we aim to provide insight on both the applications of metabolic engineering for natural product biosynthesis as well as optimization methods.

A Myo-Inositol-Inducible Expression System for Corynebacterium glutamicum and Its Application.

Corynebacterium glutamicum is one of the important industrial microorganisms for production of amino acids and other value-added compounds. Most expression vectors used in C. glutamicum are based on inducible promoter (P tac or P trc ) activated by isopropyl-β-D-thiogalactopyranoside (IPTG). However, these vectors seem unsuitable for large-scale industrial production due to the high cost and toxicity of IPTG. Myo-inositol is an ideal inducer because of its non-toxicity and lower price. In this study, a myo-inositol-inducible expression vector pMI-4, derived from the expression vector pXMJ19, was constructed. Besides the original chloramphenicol resistance gene cat, multiple cloning sites, and rrnB terminator, the pMI-4 (6,643 bp) contains the iolR q cassette and the myo-inositol-inducible promoter P iolT1 . The pMI-4 could stably replicate in the C. glutamicum host. Meanwhile, the non-myo-inositol degradation host strain C. glutamicumΔiolGΔoxiCΔoxiDΔoxiE for maintaining the pMI-4 was developed. Overexpression of hemA M and hemL using pMI-4 resulted in a significant accumulation of 5-aminolevulinic acid, indicating its potential application in metabolic engineering and industrial fermentation.

Electrochemical characterization of mutant forms of rubredoxin B from Mycobacterium tuberculosis

Electron transfer in metalloproteins is a driving force for many biological processes and widely distributed in nature. Rubredoxin B (RubB) from Mycobacterium tuberculosis is a first example among [1Fe-0S] proteins that support catalytic activity of terminal sterol-monooxygenases enabling its application in metabolic engineering. To explore the tolerance of RubB to the specific amino acid changes we evaluated the effect of surface mutations on its electrochemical properties. Based on the RubB fold we also designed the mutant with a putative additional site for protein-protein interactions to further evaluate electron transfer and electrochemical properties. The investigation of redox properties of mutant variants of RubB was done using screen-printed graphite electrodes (SPEs) modified with stable dispersion of multi-walled carbon nanotubes (MWCNTs). The redox potentials (midpoint potentials, E0Ꞌ) of mutants did not significantly differ from the wild type protein and vary in the range of −264 to −231 mV vs. Ag/AgCl electrode. However, all mutations affect electron transfer rate between the protein and electrode. Notably, the modulation of the protein-protein interactions was observed for the insertion mutant suggesting the possibility of tailoring of rubredoxin for the selected redox-partner. Overall, RubB is tolerant to the significant modifications in its structure enabling rational engineering of novel redox proteins.

Increasing Lovastatin Production by Re-routing the Precursors Flow of Aspergillus terreus via Metabolic Engineering.

Lovastatin is an anti-cholesterol medicine that is commonly prescribed to manage cholesterol levels, and minimise the risk of suffering from heart-related diseases. Aspergillus terreus (ATCC 20542) supplied with carbohydrates or sugar alcohols can produce lovastatin. The present work explored the application of metabolic engineering in A. terreus to re-route the precursor flow towards the lovastatin biosynthetic pathway by simultaneously overexpressing the gene for acetyl-CoA carboxylase (acc) to increase the precursor flux, and eliminate ( +)-geodin biosynthesis (a competing secondary metabolite) by removing the gene for emodin anthrone polyketide synthase (gedC). Alterations to metabolic flux in the double mutant (gedCΔ*accox) strain and the effects of using two different substrate formulations were examined. The gedCΔ*accox strain, when cultivated with a mixture of glycerol and lactose, significantly (p < 0.05) increased the levels of metabolic precursors malonyl-CoA (48%) and acetyl-CoA (420%), completely inhibited the (+)-geodin biosynthesis, and increased the level of lovastatin [152mg/L; 143% higher than the wild-type (WT) strain]. The present work demonstrated how the manipulation of A. terreus metabolic pathways could increase the efficiency of carbon flux towards lovastatin, thus elevating its overall production and enabling the use of glycerol as a substrate source. As such, the present work also provides a framework model for other medically or industrially important fungi to synthesise valuable compounds using sustainable carbon sources.

Identification and Validation of Four Novel Promoters for Gene Engineering with Broad Suitability across Species.

The transcriptional capacities of target genes are strongly influenced by promoters, whereas few studies have focused on the development of robust, high-performance and cross-species promoters for wide application in different bacteria. In this work, four novel promoters (Pk.rtufB, Pk.r1, Pk.r2, and Pk.r3) were predicted from Ketogulonicigenium robustum and their inconsistency in the -10 and -35 region nucleotide sequences indicated they were different promoters. Their activities were evaluated by using green fluorescent protein (gfp) as a reporter in different species of bacteria, including K. vulgare SPU B805, Pseudomonas putida KT2440, Paracoccus denitrificans PD1222, Bacillus licheniformis and Raoultella ornithinolytica, due to their importance in metabolic engineering. Our results showed that the four promoters had different activities, with Pk.r1 showing the strongest activity in almost all of the experimental bacteria. By comparison with the commonly used promoters of E. coli (tufB, lac, lacUV5), K. vulgare (Psdh, Psndh) and P. putida KT2440 (JE111411), the four promoters showed significant differences due to only 12.62% nucleotide similarities, and relatively higher ability in regulating target gene expression. Further validation experiments confirmed their ability in initiating the target minCD cassette because of the shape changes under the promoter regulation. The overexpression of sorbose dehydrogenase and cytochrome c551 by Pk.r1 and Pk.r2 resulted in a 22.75% enhancement of 2-KGA yield, indicating their potential for practical application in metabolic engineering. This study demonstrates an example of applying bioinformatics to find new biological components for gene operation and provides four novel promoters with broad suitability, which enriches the usable range of promoters to realize accurate regulation in different genetic backgrounds.

Modular and Molecular Optimization of a LOV (Light-Oxygen-Voltage)-Based Optogenetic Switch in Yeast.

Optogenetic switches allow light-controlled gene expression with reversible and spatiotemporal resolution. In Saccharomyces cerevisiae, optogenetic tools hold great potential for a variety of metabolic engineering and biotechnology applications. In this work, we report on the modular optimization of the fungal light–oxygen–voltage (FUN-LOV) system, an optogenetic switch based on photoreceptors from the fungus Neurospora crassa. We also describe new switch variants obtained by replacing the Gal4 DNA-binding domain (DBD) of FUN-LOV with nine different DBDs from yeast transcription factors of the zinc cluster family. Among the tested modules, the variant carrying the Hap1p DBD, which we call “HAP-LOV”, displayed higher levels of luciferase expression upon induction compared to FUN-LOV. Further, the combination of the Hap1p DBD with either p65 or VP16 activation domains also resulted in higher levels of reporter expression compared to the original switch. Finally, we assessed the effects of the plasmid copy number and promoter strength controlling the expression of the FUN-LOV and HAP-LOV components, and observed that when low-copy plasmids and strong promoters were used, a stronger response was achieved in both systems. Altogether, we describe a new set of blue-light optogenetic switches carrying different protein modules, which expands the available suite of optogenetic tools in yeast and can additionally be applied to other systems.

The Neurospora crassa Inducible Q System Enables Simultaneous Optogenetic Amplification and Inversion in Saccharomyces cerevisiae for Bidirectional Control of Gene Expression.

Bidirectional optogenetic control of yeast gene expression has great potential for biotechnological applications. Our group has developed optogenetic inverter circuits that activate transcription using darkness, as well as amplifier circuits that reach high expression levels under limited light. However, because both types of circuits harness Gal4p and Gal80p from the galactose (GAL) regulon they cannot be used simultaneously. Here, we apply the Q System, a transcriptional activator/inhibitor system from Neurospora crassa, to build circuits in Saccharomyces cerevisiae that are inducible using quinic acid, darkness, or blue light. We develop light-repressed OptoQ-INVRT circuits that initiate darkness-triggered transcription within an hour of induction, as well as light-activated OptoQ-AMP circuits that achieve up to 39-fold induction. The Q System does not exhibit crosstalk with the GAL regulon, allowing coutilization of OptoQ-AMP circuits with previously developed OptoINVRT circuits. As a demonstration of practical applications in metabolic engineering, we show how simultaneous use of these circuits can be used to dynamically control both growth and production to improve acetoin production, as well as enable light-tunable co-production of geraniol and linalool, two terpenoids implicated in the hoppy flavor of beer. OptoQ-AMP and OptoQ-INVRT circuits enable simultaneous optogenetic signal amplification and inversion, providing powerful additions to the yeast optogenetic toolkit.

Biopolymer production in microbiology by application of metabolic engineering

Biopolymer production in microbiology by application of metabolic engineering

Efficient 5-aminolevulinic acid production through reconstructing the metabolic pathway in SDH-deficient Yarrowia lipolytica

5-Aminolevulinic acid (5-ALA) is a precursor for the biosynthesis of tetrapyrrole compounds such as chlorophyll a, heme, and vitamin B12, which has been widely used in the fields of agriculture and medicine. 5-ALA can be biosynthesized through C4 pathway that use succinyl-CoA and glycine as precursor, or through C5 pathway that use glutamate as precursor. Yarrowia lipolytica is an important unconventional yeast and has wide applications in metabolic engineering and industrial biotechnology. It possesses strong metabolic flux through tricarboxylic acid cycle, and prominent acid tolerance, which make it an attractive chassis cell for 5-ALA fermentation. However, there are no reports on the 5-ALA production in Y. lipolytica so far. In this study, a series of 5-ALA producing engineered strains were constructed by using succinate dehydrogenase (SDH)-deficient Y. lipolytica. The related genes of C4 and C5 pathway were co-expressed, and the best engineered strain PGC62-IAL (MatA, xpr2–322, axp-2, leu2–270, ura3–302, ΔSdh5::loxP, ΔAch1::loxP, ScPck, ScHemⅠ, StHemA, EcHemL) for efficient ALA production was obtained. Through optimizing culture conditions, the titer of 5-ALA was 1050 mg/L in shake flask fermentation with glycerol as carbon source. Finally, the 5-ALA titer reached 2216.8 mg/L in the fed-batch fermentation, which is the highest 5-ALA titer achieved using yeast globally. Due to accumulation of the by-products including succinic acid and porphyrin compounds, the 5-ALA yield only reached 0.024 g/g glucose. Nevertheless, Y. lipolytica was engineered to produce 5-ALA for the first time, and indicated that SDH-deficient strains can be used as platform for efficient 5-ALA production.

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability.

Since the industrial revolution, the rapid growth and development of global industries have depended largely upon the utilization of coal-derived chemicals, and more recently, the utilization of petroleum-based chemicals. These developments have followed a linear economy model (produce, consume, and dispose). As the world is facing a serious threat from the climate change crisis, a more sustainable solution for manufacturing, i.e., circular economy in which waste from the same or different industries can be used as feedstocks or resources for production offers an attractive industrial/business model. In nature, biological systems, i.e., microorganisms routinely use their enzymes and metabolic pathways to convert organic and inorganic wastes to synthesize biochemicals and energy required for their growth. Therefore, an understanding of how selected enzymes convert biobased feedstocks into special (bio)chemicals serves as an important basis from which to build on for applications in biocatalysis, metabolic engineering, and synthetic biology to enable biobased processes that are greener and cleaner for the environment. This review article highlights the current state of knowledge regarding the enzymatic reactions used in converting biobased wastes (lignocellulosic biomass, sugar, phenolic acid, triglyceride, fatty acid, and glycerol) and greenhouse gases (CO2 and CH4) into value-added products and discusses the current progress made in their metabolic engineering. The commercial aspects and life cycle assessment of products from enzymatic and metabolic engineering are also discussed. Continued development in the field of metabolic engineering would offer diversified solutions which are sustainable and renewable for manufacturing valuable chemicals.

Harnessing the Endogenous 2μ Plasmid of Saccharomyces cerevisiae for Pathway Construction.

pRS episomal plasmids are widely used in Saccharomyces cerevisiae, owing to their easy genetic manipulations and high plasmid copy numbers (PCNs). Nevertheless, their broader application is hampered by the instability of the pRS plasmids. In this study, we designed an episomal plasmid based on the endogenous 2μ plasmid with both improved stability and increased PCN, naming it p2μM, a 2μ-modified plasmid. In the p2μM plasmid, an insertion site between the REP1 promoter and RAF1 promoter was identified, where the replication (ori) of Escherichia coli and a selection marker gene of S. cerevisiae were inserted. As a proof of concept, the tyrosol biosynthetic pathway was constructed in the p2μM plasmid and in a pRS plasmid (pRS423). As a result, the p2μM plasmid presented lower plasmid loss rate than that of pRS423. Furthermore, higher tyrosol titers were achieved in S. cerevisiae harboring p2μM plasmid carrying the tyrosol pathway-related genes. Our study provided an improved genetic manipulation tool in S. cerevisiae for metabolic engineering applications, which may be widely applied for valuable product biosynthesis in yeast.

Analysis of the Innovation Trend in Cell-Free Synthetic Biology.

Cell-free synthetic biology is a maturing field that aims to assemble biomolecular reactions outside cells for compelling applications in drug discovery, metabolic engineering, biomanufacturing, diagnostics, and education. Cell-free systems have several key features. They circumvent mechanisms that have evolved to facilitate species survival, bypass limitations on molecular transport across the cell wall, enable high-yielding and rapid synthesis of proteins without creating recombinant cells, and provide high tolerance towards toxic substrates or products. Here, we analyze ~750 published patents and ~2000 peer-reviewed manuscripts in the field of cell-free systems. Three hallmarks emerged. First, we found that both patent filings and manuscript publications per year are significantly increasing (five-fold and 1.5-fold over the last decade, respectively). Second, we observed that the innovation landscape has changed. Patent applications were dominated by Japan in the early 2000s before shifting to China and the USA in recent years. Finally, we discovered an increasing prevalence of biotechnology companies using cell-free systems. Our analysis has broad implications on the future development of cell-free synthetic biology for commercial and industrial applications.

Modification of DNA regions with metagenomic DNA fragments (MDRMDF): A convenient strategy for efficient protein engineering

In this study, we have established a convenient and efficient approach named Modification of DNA Regions with Metagenomic DNA Fragments (MDRMDF) for protein engineering. Degenerate primers were designed corresponding to conserved regions of the gene of interest which were used for amplification of fragments with template of the metagenomic DNA. The resulting PCR products were used to replace the corresponding regions of the gene of interest to introduce modified gene for function-based screening. Therefore, this method can make full use of the metagenomic DNA sequences with unknown metagenomic gene information for efficient protein engineering. The β-xylosidase BH3683 was used to construct a MDRMDF library which was screened with a newly designed p-NPX-M9 medium-based strategy. As a result, a mutant protein Xyl-M56 showing high activity, improved pH stability and higher tolerance to organic solvents was obtained which may have potential for industrial application. The MDRMDF method may find wide application in enzyme engineering, metabolic engineering and other fields, especially offering a new methodological option for the directed evolution of proteins.

Thirty years development of metabolic engineering: a review

Since its establishment 30 years ago, the discipline of metabolic engineering has developed rapidly based on its deep integration with molecular biology, systems biology and synthetic biology successively, which has greatly contributed to advancing and upgrading biotechnology industry. This review firstly analyzes the current status of academic research and China's competence in the area of metabolic engineering according to the data of papers published in SCI-indexed journals in the past 30 years. Subsequently, the article summarizes the development of systems biology methods and enabling technologies of synthetic biology and their applications in metabolic engineering in the past 10 years. Finally, the major challenges and future perspectives for the development of metabolic engineering are briefly discussed.

Metabolic engineering tools for Saccharomyces cerevisiae

Since its birth in the early 1990s, metabolic engineering technology has gone 30 years rapid development. As one of the preferred chassis for metabolic engineering, S. cerevisiae cells have been engineered into microbial cell factories for the production of a variety of bulk chemicals and novel high value-added bioactive compounds. In recent years, synthetic biology, bioinformatics, machine learning and other technologies have also greatly contributed to the technological development and applications of metabolic engineering. This review summarizes the important technological development for metabolic engineering of S. cerevisiae in the past 30 years. Firstly, classical metabolic engineering tools and strategies were reviewed, followed by reviewing systems metabolic engineering and synthetic biology driven metabolic engineering approaches. The review is concluded with discussing future perspectives for metabolic engineering of S. cerevisiae in the light of state-of-the-art technological development.

An evolving and flourishing metabolic engineering

In 1990s, Bailey and Stephanopoulos put forward the concept of classic metabolic engineering, aiming to use DNA recombination technology to rewire metabolic network to achieve improved cell performance and increased target products. In the last 30 years since the birth of metabolic engineering, life science have flourished, and new disciplines such as genomics, systems biology and synthetic biology have emerged, injecting new connotations and vitality into the development of metabolic engineering. Classic metabolic engineering research has entered into an unprecedented stage of systems metabolic engineering. The application of synthetic biology tools and strategies, such as omics technology, genomic-scale metabolic model, parts assembly, circuits design, dynamic control, genome editing and many others, have greatly improved the design, build, and rewiring capabilities of complex metabolism. The intervention of machine learning and the combination of evolutionary engineering and metabolic engineering will further promote the development of systems metabolic engineering. This paper analyzes the development of metabolic engineering in the past 30 years and summarizes the novel theories, techniques, strategies, and applications of metabolic engineering that have emerged over the past 30 years.

Enhanced targeted DNA methylation of the CMV and endogenous promoters with dCas9-DNMT3A3L entails distinct subsequent histone modification changes in CHO cells

With the emergence of new CRISPR/dCas9 tools that enable site specific modulation of DNA methylation and histone modifications, more detailed investigations of the contribution of epigenetic regulation to the precise phenotype of cells in culture, including recombinant production subclones, is now possible. These also allow a wide range of applications in metabolic engineering once the impact of such epigenetic modifications on the chromatin state is available.In this study, enhanced DNA methylation tools were targeted to a recombinant viral promoter (CMV), an endogenous promoter that is silenced in its native state in CHO cells, but had been reactivated previously (β-galactoside α-2,6-sialyltransferase 1) and an active endogenous promoter (α-1,6-fucosyltransferase), respectively. Comparative ChIP-analysis of histone modifications revealed a general loss of active promoter histone marks and the acquisition of distinct repressive heterochromatin marks after targeted methylation. On the other hand, targeted demethylation resulted in autologous acquisition of active promoter histone marks and loss of repressive heterochromatin marks. These data suggest that DNA methylation directs the removal or deposition of specific histone marks associated with either active, poised or silenced chromatin. Moreover, we show that de novo methylation of the CMV promoter results in reduced transgene expression in CHO cells. Although targeted DNA methylation is not efficient, the transgene is repressed, thus offering an explanation for seemingly conflicting reports about the source of CMV promoter instability in CHO cells.Importantly, modulation of epigenetic marks enables to nudge the cell into a specific gene expression pattern or phenotype, which is stabilized in the cell by autologous addition of further epigenetic marks. Such engineering strategies have the added advantage of being reversible and potentially tunable to not only turn on or off a targeted gene, but also to achieve the setting of a desirable expression level.