Engineering the Cad pathway in Escherichia coli to produce glutarate from L-lysine

Systems engineering of Escherichia coli for high-level glutarate production from glucose

Glutarate is a key monomer in polyester and polyamide production. The low efficiency of the current biosynthetic pathways hampers its production by microbial cell factories. Herein, through metabolic simulation, a lysine-overproducing E. coli strain Lys5 is engineered, achieving titer, yield, and productivity of 195.9 g/L, 0.67 g/g glucose, and 5.4 g/L·h, respectively. Subsequently, the pathway involving aromatic aldehyde synthase, monoamine oxidase, and aldehyde dehydrogenase (AMA pathway) is introduced into E. coli Lys5 to produce glutarate from glucose. To enhance the pathway's efficiency, rational mutagenesis on the aldehyde dehydrogenase is performed, resulting in the development of variant Mu5 with a 50-fold increase in catalytic efficiency. Finally, a glutarate tolerance gene cbpA is identified and genomically overexpressed to enhance glutarate productivity. With enzyme expression optimization, the glutarate titer, yield, and productivity of E. coli AMA06 reach 88.4 g/L, 0.42 g/g glucose, and 1.8 g/L·h, respectively. These findings hold implications for improving glutarate biosynthesis efficiency in microbial cell factories.

Enabling pathway design by multiplex experimentation and machine learning

The remarkable metabolic diversity observed in nature has provided a foundation for sustainable production of a wide array of valuable molecules. However, transferring the biosynthetic pathway to the desired host often runs into inherent failures that arise from intermediate accumulation and reduced flux resulting from competing pathways within the host cell. Moreover, the conventional trial and error methods utilized in pathway optimization struggle to fully grasp the intricacies of installed pathways, leading to time-consuming and labor-intensive experiments, ultimately resulting in suboptimal yields. Considering these obstacles, there is a pressing need to explore the enzyme expression landscape and identify the optimal pathway configuration for enhanced production of molecules. This review delves into recent advancements in pathway engineering, with a focus on multiplex experimentation and machine learning techniques. These approaches play a pivotal role in overcoming the limitations of traditional methods, enabling exploration of a broader design space and increasing the likelihood of discovering optimal pathway configurations for enhanced production of molecules. We discuss several tools and strategies for pathway design, construction, and optimization for sustainable and cost-effective microbial production of molecules ranging from bulk to fine chemicals. We also highlight major successes in academia and industry through compelling case studies.

Recent Progress in Metabolic Engineering of Escherichia coli for the Production of Various C4 and C5-Dicarboxylic Acids

As an alternative to petrochemical synthesis, well-established industrial microbes, such as Escherichia coli, are employed to produce a wide range of chemicals, including dicarboxylic acids (DCAs), which have significant potential in diverse areas including biodegradable polymers. The demand for biodegradable polymers has been steadily rising, prompting the development of efficient production pathways on four- (C4) and five-carbon (C5) DCAs derived from central carbon metabolism to meet the increased demand via the biosynthesis. In this context, E. coli is utilized to produce these DCAs through various metabolic engineering strategies, including the design or selection of metabolic pathways, pathway optimization, and enhancement of catalytic activity. This review aims to highlight the recent advancements in metabolic engineering techniques for the production of C4 and C5 DCAs in E. coli.

A Multi-Enzyme Cascade for Efficient Production of Pyrrolidone from l-Glutamate

Pyrrolidone is a high value-added monomer and an important active drug intermediate. However, the efficient enzymatic synthesis of pyrrolidone remains a challenge. Here, we developed and reconstructed a three-enzyme cascade pathway using Escherichia coli BL21(DE3) for the production of pyrrolidone from l-glutamate (l-Glu). The carnitine-CoA ligase from Escherichia coli (EcCaiC) at a low expression level and with a low activity is regarded as the rate-limiting enzyme. Here, we obtained the best EcCaiCF380M/N430D double mutant with a kcat/Km value 1.5 times higher than that of the wild type via mechanism-based protein engineering. For this, we (i) eliminated the steric hindrance of the loop ring to improve the precatalytic conformation of the adenylation intermediate and (ii) fixed the hinge region to stabilize the closed conformation of the enzyme. Furthermore, ribosome-binding site (RBS) optimization led to an increase in the expression level of EcCaiCF380M/N430D, which was then cloned into the plasmid pET-EcCaiCF380M/N430D-DegoPPK2. Finally, under optimal induction and transformation conditions, 16.62 g/L of pyrrolidone was generated from 30 g/L l-Glu (batch feeding) within 24 h with a molar conversion rate of 95.2% and the highest productivity ever obtained, to our knowledge (0.69 g/L/h). Our findings demonstrate a strategy that is potentially attractive for the industrial production of pyrrolidone. IMPORTANCE This study developed a three-enzyme cascade pathway for the production of pyrrolidone from l-Glu. The catalytic efficiency of carnitine CoA ligase from Escherichia coli (EcCaiC) was improved by mechanism-based protein engineering, and the titer of pyrrolidone was further increased by ribosome-binding site (RBS), induction conditions, and conversion conditions optimization. Finally, we efficiently produced pyrrolidone by one pot in vivo with 95.2% conversion and 0.69 g/L/h productivity. Our study provides a new possibility for the industrial production of enzymatic synthesis of pyrrolidone.

Engineering Microorganisms to Produce Bio-Based Monomers: Progress and Challenges

Bioplastics are polymers made from sustainable bio-based feedstocks. While the potential of producing bio-based monomers in microbes has been investigated for decades, their economic feasibility is still unsatisfactory compared with petroleum-derived methods. To improve the overall synthetic efficiency of microbial cell factories, three main strategies were summarized in this review: firstly, implementing approaches to improve the microbial utilization ability of cheap and abundant substrates; secondly, developing methods at enzymes, pathway, and cellular levels to enhance microbial production performance; thirdly, building technologies to enhance microbial pH, osmotic, and metabolites stress tolerance. Moreover, the challenges of, and some perspectives on, exploiting microorganisms as efficient cell factories for producing bio-based monomers are also discussed.

An artificial pathway for trans-4-hydroxy-L-pipecolic acid production from L-lysine in Escherichia coli

Trans-4-hydroxy-L-pipecolic acid (Trans-4-HyPip) is a hydroxylated product of L-pipecolic acid, and which is widely used in pharmaceutical and chemical industry. Here, a trans-4-HyPip biosynthesis module was designed and constructed in Escherichia coli by overexpressing lysine α-oxidase, Δ1-piperideine-2-carboxylase reductase, glucose dehydrogenase, lysine permease, catalase and L-pipecolic acid trans-4-hydroxylase for expanding the lysine catabolism pathway. 4.89 g/L of trans-4-HyPip was generated in shake flasks from 8 g/L of L-pipecolic acid. By this approach, 14.86 g/L of trans-4-HyPip was produced from lysine after 48 h in a 5-L bioreactor. As far as we know, this is the first multi-enzyme cascade catalytic system for the production of trans-4-HyPip using Escherichia coli from L-lysine. Therefore, it can be considered as a potential candidate for industrial production of trans-4-HyPip in microorganisms.

Efficient production of inositol from glucose via a tri-enzymatic cascade pathway

Inositol is an essential intermediate in cosmetics, food, medicine and other industries. However, developing an efficient biotransformation system for large-scale production of inositol remains challenging. Herein, a tri-enzymatic cascade route with three novel enzymes including polyphosphate glucokinase (PPGK) from Thermobifida fusca, inositol 3-phosphate synthase (IPS) from Archaeoglobus profundus DSM 5631 and inositol monophosphatase (IMP) from Thermotoga petrophila RKU-1 was designed and reconstructed for the production of inositol from glucose. The problem of poor cooperativity of the cascade reactions was addressed by ribosome binding site (RBS) optimization of PPGK and replication of IPS. Under the optimum biotransformation conditions, the engineered whole-cell immobilized with colloidal chitin transformed 120 g/L glucose to 110.8 g/L inositol with 92.3% conversion in four cycles of reuse, representing the highest titer of inositol to date. Furthermore, this is the first study for inositol production using a three-enzyme coordinated immobilized single-cell.

An Artificial Pathway for N-Hydroxy-Pipecolic Acid Production From L-Lysine in Escherichia coli

N-hydroxy-pipecolic acid (NHP) is a hydroxylated product of pipecolic acid and an important systemic acquired resistance signal molecule. However, the biosynthesis of NHP does not have a natural metabolic pathway in microorganisms. Here, we designed and constructed a promising artificial pathway in Escherichia coli for the first time to produce NHP from biomass-derived lysine. This biosynthesis route expands the lysine catabolism pathway and employs six enzymes to sequentially convert lysine into NHP. This artificial route involves six functional enzyme coexpression: lysine α-oxidase from Scomber japonicus (RaiP), glucose dehydrogenase from Bacillus subtilis (GDH), Δ¹-piperideine-2-carboxylase reductase from Pseudomonas putida (DpkA), lysine permease from E. coli (LysP), flavin-dependent monooxygenase (FMO1), and catalase from E. coli (KatE). Moreover, different FMO1s are used to evaluate the performance of the produce NHP. A titer of 111.06 mg/L of NHP was yielded in shake flasks with minimal medium containing 4 g/L of lysine. By this approach, NHP has so far been produced at final titers reaching 326.42 mg/L by 48 h in a 5-L bioreactor. To the best of our knowledge, this is the first NHP process using E. coli and the first process to directly synthesize NHP by microorganisms. This study lays the foundation for the development and utilization of renewable resources to produce NHP in microorganisms.

Engineering a CRISPRi Circuit for Autonomous Control of Metabolic Flux in Escherichia coli

Building autonomous switches is an effective approach for rewiring metabolic flux during microbial synthesis of chemicals. However, current autonomous switches largely rely on metabolite-responsive biosensors or quorum-sensing circuits. In this study, a stationary phase promoter (SPP) and a protein degradation tag (PDT) were combined with the CRISPR interference (CRISPRi) system to construct an autonomous repression system that could shut down multiple-gene expression depending on the cellular physiological state. With this autonomous CRISPRi system to regulate one target gene, a fermenter-scale titer of shikimic acid reached 21 g/L, which was the highest titer ever reported by Escherichia coli in a minimal medium without any chemical inducers. With three target genes repressed, 26 g/L glutaric acid could be achieved with decreased byproduct accumulation. These results highlight the applicability of the autonomous CRISPRi system for microbial production of value-added chemicals.

Utilization of a Wheat Sidestream for 5-Aminovalerate Production in Corynebacterium glutamicum

Production of plastics from petroleum-based raw materials extensively contributes to global pollution and CO2 emissions. Biotechnological production of functionalized monomers can reduce the environmental impact, in particular when using industrial sidestreams as feedstocks. Corynebacterium glutamicum, which is used in the million-ton-scale amino acid production, has been engineered for sustainable production of polyamide monomers. In this study, wheat sidestream concentrate (WSC) from industrial starch production was utilized for production of l-lysine-derived bifunctional monomers using metabolically engineered C. glutamicum strains. Growth of C. glutamicum on WSC was observed and could be improved by hydrolysis of WSC. By heterologous expression of the genes xylA Xc B Cg (xylA from Xanthomonas campestris) and araBAD Ec from E. coli, xylose, and arabinose in WSC hydrolysate (WSCH), in addition to glucose, could be consumed, and production of l-lysine could be increased. WSCH-based production of cadaverine and 5-aminovalerate (5AVA) was enabled. To this end, the lysine decarboxylase gene ldcC Ec from E. coli was expressed alone or for conversion to 5AVA cascaded either with putrescine transaminase and dehydrogenase genes patDA Ec from E. coli or with putrescine oxidase gene puo Rq from Rhodococcus qingshengii and patD Ec . Deletion of the l-glutamate dehydrogenase-encoding gene gdh reduced formation of l-glutamate as a side product for strains with either of the cascades. Since the former cascade (ldcC Ec -patDA Ec ) yields l-glutamate, 5AVA production is coupled to growth by flux enforcement resulting in the highest 5AVA titer obtained with WSCH-based media.