Migration of glutamate decarboxylase by cold treatment on whole-cell biocatalyst triggered activity for 4-aminobutyric acid production in engineering Escherichia coli

Advances in engineering and applications of microbial glutamate decarboxylases for gamma-aminobutyric acid production

Gamma-aminobutyric acid (GABA) is a key neurotransmitter with significant health benefits, including anxiolytic and anti-hypertensive effects, and potential use in biodegradable material synthesis. The increasing market demand for GABA has intensified the search for cost-effective production methods. The key enzyme involved in GABA production is glutamate decarboxylase (GAD), which catalyzes the conversion of L-glutamate to GABA. GAD plays a central role in various production approaches, such as enzyme-based catalysis, whole-cell catalysis, and microbial fermentation. Although microbial GADs are preferred for their high catalytic activity, their low pH and thermal stability present significant challenges for large-scale GABA production. Wild-type GADs typically have an optimal pH range of 4-5, and their activity sharply declines as the pH increases, thereby reducing production efficiency. Furthermore, GADs' poor thermal stability makes them vulnerable to temperature fluctuations during industrial processes, further limiting GABA production. Recent research has focused on engineering GAD variants with improved stability and performance through rational design, directed evolution, and semi rational approaches. These advancements not only expand the potential applications of GAD in biocatalysis but also offer promising solutions for sustainable GABA production. This paper provides an in-depth review of the engineering of GADs, applications of GAD in GABA production, and strategies to overcome limitations, offering a comprehensive overview of the current state and future prospects of GAD modification in enhancing GABA production.

Engineered Halomonas for production of gamma-aminobutyric acid and 2-pyrrolidone

Gamma-Aminobutyric acid (GABA) is a derivative of L-glutamate, also a precursor for the synthesis of 2-pyrrolidone, which is a monomer of nylon-4. This study achieved a one-step biosynthesis of GABA and 2-pyrrolidone by Halomonas bluephagenesis overexpressing key genes involved in GABA and 2-pyrrolidone synthesis and deleting GABA degradation genes combined with reducing the degradation of 2-pyrrolidone precursor. The resulting H. bluephagenesis strain WLp07 was employed in whole-cell catalysis, producing 357 g/L of GABA and 72 wt% of PHA. Furthermore, a self-flocculating H. bluephagenesis allowed rapid, convenient recycling of the cells, achieving 880 g/L of GABA over three cycles. Shake flask studies showed that engineered H. bluephagenesis harboring β-alanine CoA transferase was able to synthesized 2-pyrrolidone from GABA. H. bluephagenesis as a chassis of next generation industrial biotechnology (NGIB), demonstrated its diverse ability to produce GABA and 2-pyrrolidone in addition to intracellular PHA.

Microbial chassis design and engineering for production of gamma-aminobutyric acid

Gamma-aminobutyric acid (GABA) is a non-protein amino acid which is widely applied in agriculture and pharmaceutical additive industries. GABA is synthesized from glutamate through irreversible α-decarboxylation by glutamate decarboxylase. Recently, microbial synthesis has become an inevitable trend to produce GABA due to its sustainable characteristics. Therefore, reasonable microbial platform design and metabolic engineering strategies for improving production of GABA are arousing a considerable attraction. The strategies concentrate on microbial platform optimization, fermentation process optimization, rational metabolic engineering as key metabolic pathway modification, promoter optimization, site-directed mutagenesis, modular transporter engineering, and dynamic switch systems application. In this review, the microbial producers for GABA were summarized, including lactic acid bacteria, Corynebacterium glutamicum, and Escherichia coli, as well as the efficient strategies for optimizing them to improve the production of GABA.

Recent advances in the biosynthesis and industrial biotechnology of Gamma-amino butyric acid

GABA (Gamma-aminobutyric acid), a crucial neurotransmitter in the central nervous system, has gained significant attention in recent years due to its extensive benefits for human health. The review focused on recent advances in the biosynthesis and production of GABA. To begin with, the investigation evaluates GABA-producing strains and metabolic pathways, focusing on microbial sources such as Lactic Acid Bacteria, Escherichia coli, and Corynebacterium glutamicum. The metabolic pathways of GABA are elaborated upon, including the GABA shunt and critical enzymes involved in its synthesis. Next, strategies to enhance microbial GABA production are discussed, including optimization of fermentation factors, different fermentation methods such as co-culture strategy and two-step fermentation, and modification of the GABA metabolic pathway. The review also explores methods for determining glutamate (Glu) and GABA levels, emphasizing the importance of accurate quantification. Furthermore, a comprehensive market analysis and prospects are provided, highlighting current trends, potential applications, and challenges in the GABA industry. Overall, this review serves as a valuable resource for researchers and industrialists working on GABA advancements, focusing on its efficient synthesis processes and various applications, and providing novel ideas and approaches to improve GABA yield and quality.

Microbial itaconic acid bioproduction towards sustainable development: Insights, challenges, and prospects

Microbial biomanufacturing is a promising approach to produce high-value compounds with low-carbon footprint and significant economic benefits. Among twelve "Top Value-Added Chemicals from Biomass", itaconic acid (IA) stands out as a versatile platform chemical with numerous applications. IA is naturally produced by Aspergillus and Ustilago species through a cascade enzymatic reaction between aconitase (EC 4.2.1.3) and cis-aconitic acid decarboxylase (EC 4.1.1.6). Recently, non-native hosts such as Escherichia coli, Corynebacterium glutamicum, Saccharomyces cerevisiae, and Yarrowia lipolytica have been genetically engineered to produce IA through the introduction of key enzymes. This review provides an up-to-date summary of the progress made in IA bioproduction, from native to engineered hosts, covers in vivo and in vitro approaches, and highlights the prospects of combination tactics. Current challenges and recent endeavors are also addressed to envision comprehensive strategies for renewable IA production in the future towards sustainable development goals (SDGs).

High-level itaconic acid (IA) production using engineered Escherichia coli Lemo21(DE3) toward sustainable biorefinery

Itaconic acid (IA) serves as a prominent building block for polyamides as sustainable material. In vivo IA production is facing the competing side reactions, byproducts accumulation, and long cultivation time. Therefore, the utilization of whole-cell biocatalysts to carry out production from citrate is an alternative approach to sidestep the current limitations. In this study, in vitro reaction of IA was obtained 72.44 g/L by using engineered E. coli Lemo21(DE3) harboring the aconitase (Acn, EC 4.2.1.3) and cis-aconitate decarboxylase (CadA, EC 4.1.1.6) which was cultured in glycerol-based minimal medium. IA productivity enhancement was observed after cold-treating the biocatalysts in - 80 °C for 24 h prior to the reaction, reaching 81.6 g/L. On the other hand, a new seeding strategy in Terrific Broth (TB) as a nutritionally rich medium was employed to maintain the biocatalysts stability up to 30 days. Finally, the highest IA titer of 98.17 g/L was attained using L21::7G chassis, that has a pLemo plasmid and integration of GroELS to the chromosome. The high-level of IA production along with the biocatalyst reutilization enables the economic viability toward a sustainable biorefinery.

High-level production of γ-aminobutyric acid via efficient co-expression of the key genes of glutamate decarboxylase system in Escherichia coli

Biosynthesis of the functional factor γ-aminobutyric acid (GABA) in bacteria involves two key proteins an intracellular glutamate decarboxylase (GadB) and a membrane-bound antiporter (GadC). Efficient co-expression of suitable GadB and GadC candidates is crucial for improving GABA productivity. In this study, gadB ΔC11 of Lactiplantibacillus plantarum and gadC ΔC41 of Escherichia coli were inserted into the designed double promoter (P T7lac and P BAD ) expression system. Then, E. coli Lemo21(DE3) was chosen as the host to minimize the toxic effects of GadCΔC41 overexpression. Furthermore, a green and high-efficiency GABA synthesis system using dormant engineered Lemo21(DE3) cells as biocatalysts was developed. The total GABA yield reached 829.08 g/L with a 98.7% conversion ratio within 13 h, when engineered E. coli Lemo21(DE3) cells were concentrated to an OD600 of 20 and reused for three cycles in a 3 M L-glutamate solution at 37 °C, which represented the highest GABA productivity ever reported. Overall, expanding the active pH ranges of GadB and GadC toward physiological pH and employing a tunable expression host for membrane-bound GadC production is a promising strategy for high-level GABA biosynthesis in E. coli.

Investigation of enzymatic quality and quantity using pyridoxal 5'-phosphate (PLP) regeneration system as a decoy in Escherichia coli

Pyridoxal 5'-phosphate (PLP), an essential cofactor for multiple enzymes, was used as a protein decoy to prompt enzyme expression and activity for the first time. The best chassis, denoted as WJK, was developed using a pyridoxal kinase (PdxK) and integrated at the HK022 phage attack site of Escherichia coli W3110. When compared with the original strain, the amount and activity of lysine decarboxylase (CadA) in WJK were significantly increased by 100 % and 120 %, respectively. When supplementary nineteen amino acids as second carbon source, cell growth and protein trade-off were observed. The transcriptional levels of genes from glycolysis to TCA cycle, adhE, argH and gdhA were dominating and redirected more flux into α-ketoglutarate, thus facilitated cell growth. Stepwise improvement was conducted with pyridoxal and nitrogen-rich medium; hence, CadA activity was increased to 60 g-cadaverine/g-dry cell weight/h. By reutilizing the whole-cell biocatalysts in two repeated reactions with the supplementation of fresh cells, a total cadaverine of 576 g/L was obtained even without additional PLP. Notably, PLP decoy augment the enzymatic activities of 5-aminolevulinic acid synthase and glutamate/lysine/arginine decarboxylases by over 100 %. Finally, a conserved PLP-binding pocket, Ser-His-Lys, was identified as a vital PLP sponge site that simultaneously improved protein quality and quantity.

Effective 5-aminolevulinic acid production via T7 RNA polymerase and RuBisCO equipped Escherichia coli W3110

Chromosome-based engineering is a superior approach for gene integration generating a stable and robust chassis. Therefore, an effective amplifier, T7 RNA polymerase (T7RNAP) from bacteriophage, has been incorporated into Escherichia coli W3110 by site-specific integration. Herein, we performed the 5-aminolevulinic acid (5-ALA) production in four T7RNAP-equipped W3110 strains using recombinant 5-aminolevulinic synthase and further explored the metabolic difference in best strain. The fastest glucose consumption resulted in the highest biomass and the 5-ALA production reached to 5.5 g/L; thus, the least by-product of acetate was shown in RH strain in which T7RNAP was inserted at HK022 phage attack site. Overexpression of phosphoenolpyruvate (PEP) carboxylase would pull PEP to oxaloacetic acid in tricarboxylic acid cycle, leading to energy conservation and even no acetate production, thus, 6.53 g/L of 5-ALA was achieved. Amino acid utilization in RH deciphered the major metabolic flux in α-ketoglutaric acid dominating 5-ALA production. Finally, the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and phosphoribulokinase were expressed for carbon dioxide recycling; a robust and efficient chassis toward low-carbon assimilation and high-level of 5-ALA production up to 11.2 g/L in fed-batch fermentation was established.

Trimesic acid-modified magnetic gum as a highly efficient and recyclable biocatalyst for the one-pot green synthesis of condensation reactions

In this work, a novel and efficient magnetic biocatalyst was designed, prepared and identified using cherry tree gum as a biopolymer functionalized with 1,3,5-benzenetricarboxylic acid (gum@Fe₃O₄@BTA). The obtained biocatalyst was prepared using available and cheap materials in an easy process. This biocatalyst was used as an efficient catalyst with high catalytic activity for the synthesis of a three-component one-pot protocol and four-component one-pot protocol of tetrahydro-4H-chromene derivatives and polyhydroquinoline derivatives in EtOH green solvent under reflux conditions, respectively. The synthesized heterogeneous biocatalysts were identified and analyzed by FT-IR, EDS, FESEM, TGA and XRD techniques. The synthesis of tetrahydro-4H-chromene and polyhydroquinoline derivatives by using this biocatalyst has advantages such as high efficiency, short reaction time, simple work method, absence of dangerous solvents, environmentally friendly conditions, easy separation of the biocatalyst by an external magnet, and the ability reuse for five periods without significant decrease in catalytic activity.

Enhanced recombinant carbonic anhydrase in T7RNAP-equipped Escherichia coli W3110 for carbon capture storage and utilization (CCSU)

Sulfurihydrogenibium yellowstonense carbonic anhydrase (SyCA) is a well-known thermophilic CA for carbon mineralization. To broaden the applications of SyCA, the activity of SyCA was improved through stepwise engineering and in different cultural conditions, as well as extended to co-expression with other enzymes. The engineered W3110 strains with 4 different T7 RNA polymerase levels were employed for SyCA production. As a result, the best strain WT7L cultured in modified M9 medium with temperature shifted from 37 to 30 °C after induction increased SyCA activity to 9122 U/mL. The SyCA whole-cell biocatalyst was successfully applied for carbon capture and storage (CCS) of CaCO₃. Furthermore, SyCA was applied for low-carbon footprint synthesis of 5-aminolevulinic acid (5-ALA) and cadaverine (DAP) by coupling with ALA synthetase (ALAS) and lysine decarboxylase (CadA), suppressing CO₂ release to -6.1 g-CO₂/g-ALA and -2.53 g-CO₂/g-DAP, respectively. Harnessing a highly active SyCA offers a complete strategy for CCSU in a green process.

Sustainable production of 4-aminobutyric acid (GABA) and cultivation of Chlorella sorokiniana and Chlorella vulgaris as circular economy

The 4-aminobutyric acid (GABA) is important to produce bio-nylon 4 in biorefineries. First, a glutamate decarboxylase (GAD) was propagated in three different Escherichia coli strains to achieve 100% conversion from 1 M monosodium glutamate after optimization of the process. To make the process greener and more efficient, in situ CO₂ adaptation and citrate feeding strategies to maintain the optimal pH value and 498 g/L of GABA was obtained. However, the process releases the equivalent amount of CO₂. Therefore, CO₂ generated from GABA production was completely sequestered in sodium hydroxide to form bicarbonate and applied in a coupling culture of Chlorella sorokiniana (CS) or Chlorella vulgaris (CV) to increase the biomass when combined with sodium bicarbonate and carbonic anhydrase. Further improvement of 1.65-fold biomass and 1.43-fold lipid content were occurred when supplying GABA to the culture. This integrative process provided the highest GABA production rate without CO₂ release, forming an eco-friendly and carbon-neutral technology.