Fine-Tuning of hemB Using CRISPRi for Increasing 5-Aminolevulinic Acid Production in Escherichia coli

Metabolic engineering of Escherichia coli for the production of 5-aminolevulinic acid based on combined metabolic pathway modification and reporter-guided mutant selection (RGMS)

BACKGROUND

5-Aminolevulinic acid (ALA) recently received much attention due to its potential application in many fields such as medicine, nutrition and agriculture. Metabolic engineering is an efficient strategy to improve microbial production of 5-ALA.

RESULTS

In this study, an ALA production strain of Escherichia coli was constructed by rational metabolic engineering and stepwise improvement. A metabolic strategy to produce ALA directly from glucose in this recombinant E. coli via both C4 and C5 pathways was applied herein. The expression of a modified hemARS gene and rational metabolic engineering by gene knockouts significantly improved ALA production from 765.9 to 2056.1 mg/L. Next, we tried to improve ALA production by RGMS-directed evolution of eamA gene. After RGMS, the ALA yield of strain A2-ASK reached 2471.3 mg/L in flask. Then, we aimed to improve the oxidation resistance of cells by overexpressing sodB and katE genes and ALA yield reached 2703.8 mg/L. A final attempt is to replace original promoter of hemB gene in genome with a weaker one to decrease its expression. After 24 h cultivation, a high ALA yield of 19.02 g/L was achieved by 108-ASK in a 5 L fermenter.

CONCLUSIONS

These results suggested that an industrially competitive strain can be efficiently developed by metabolic engineering based on combined rational modification and optimization of gene expression.

Gene expression regulation by modulating Hfq expression in coordination with tailor-made sRNA-based knockdown in Escherichia coli

The tailor-made synthetic sRNA-based gene expression knockdown system has demonstrated its efficacy in achieving pathway balancing in microbes, facilitating precise target gene repression and fine-tuned control of gene expression. This system operates under a competitive mode of gene regulation, wherein the tailor-made synthetic sRNA shares the intrinsic intracellular Hfq protein with other RNAs. The limited intracellular Hfq amount has the potential to become a constraining factor in the post-transcription regulation of sRNAs. To enhance the efficiency of the tailor-made sRNA gene expression regulation platform, we introduced an Hfq expression level modulation-coordinated sRNA-based gene knockdown system. This system comprises tailor-made sRNA expression cassettes that produce varying Hfq expression levels using different strength promoters. Modulating the expression levels of Hfq significantly improved the repressing capacity of sRNA, as evidenced by evaluations with four fluorescence proteins. In order to validate the practical application of this system, we applied the Hfq-modulated sRNA-based gene knockdown cassette to Escherichia coli strains producing 5-aminolevulinic acid and L-tyrosine. Diversifying the expression levels of metabolic enzymes through this cassette resulted in substantial increases of 74.6% in 5-aminolevulinic acid and 144% in L-tyrosine production. Tailor-made synthetic sRNA-based gene expression knockdown system, coupled with Hfq copy modulation, exhibits potential for optimizing metabolic fluxes through biosynthetic pathways, thereby enhancing the production yields of bioproducts.

A comprehensive review on the recent advances for 5-aminolevulinic acid production by the engineered bacteria

5-Aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid essential for synthesizing tetrapyrrole compounds, including heme, chlorophyll, cytochrome, and vitamin B12. As a plant growth regulator, 5-ALA is extensively used in agriculture to enhance crop yield and quality. The complexity and low yield of chemical synthesis methods have led to significant interest in the microbial synthesis of 5-ALA. Advanced strategies, including the: enhancement of precursor and cofactor supply, compartmentalization of key enzymes, product transporters engineering, by-product formation reduction, and biosensor-based dynamic regulation, have been implemented in bacteria for 5-ALA production, significantly advancing its industrialization. This article offers a comprehensive review of recent developments in 5-ALA production using engineered bacteria and presents new insights to propel the field forward.

On the Possibility of Using 5-Aminolevulinic Acid in the Light-Induced Destruction of Microorganisms

Antimicrobial photodynamic inactivation (aPDI) is a method that specifically kills target cells by combining a photosensitizer and irradiation with light at the appropriate wavelength. The natural amino acid, 5-aminolevulinic acid (5-ALA), is the precursor of endogenous porphyrins in the heme biosynthesis pathway. This review summarizes the recent progress in understanding the biosynthetic pathways and regulatory mechanisms of 5-ALA synthesis in biological hosts. The effectiveness of 5-ALA-aPDI in destroying various groups of pathogens (viruses, fungi, yeasts, parasites) was presented, but greater attention was focused on the antibacterial activity of this technique. Finally, the clinical applications of 5-ALA in therapies using 5-ALA and visible light (treatment of ulcers and disinfection of dental canals) were described.

Biosynthesis, acquisition, regulation, and upcycling of heme: recent advances

Heme, an iron-containing tetrapyrrole in hemoproteins, including: hemoglobin, myoglobin, catalase, cytochrome c, and cytochrome P450, plays critical physiological roles in different organisms. Heme-derived chemicals, such as biliverdin, bilirubin, and phycocyanobilin, are known for their antioxidant and anti-inflammatory properties and have shown great potential in fighting viruses and diseases. Therefore, more and more attention has been paid to the biosynthesis of hemoproteins and heme derivatives, which depends on the adequate heme supply in various microbial cell factories. The enhancement of endogenous biosynthesis and exogenous uptake can improve the intracellular heme supply, but the excess free heme is toxic to the cells. Therefore, based on the heme-responsive regulators, several sensitive biosensors were developed to fine-tune the intracellular levels of heme. In this review, recent advances in the: biosynthesis, acquisition, regulation, and upcycling of heme were summarized to provide a solid foundation for the efficient production and application of high-value-added hemoproteins and heme derivatives.

Promoting Heme and Phycocyanin Biosynthesis in Synechocystis sp. PCC 6803 by Overexpression of Porphyrin Pathway Genes with Genetic Engineering

Due to their unique biochemical and spectroscopic properties, both heme and phycocyanobilin are widely applied in the medical and food industries. Synechocystis sp. PCC 6803 contains both heme and phycocyanin, and is capable of synthesizing phycocyanin using heme as a precursor. The aim of this study was to uncover viable metabolic targets in the porphyrin pathway from Synechocystis sp. PCC 6803 to promote the accumulation of heme and phycocyanin in the recombinant strains of microalgae. A total of 10 genes related to heme synthesis pathway derived from Synechococcus elongatus PCC 7942 and 12 genes related to endogenous heme synthesis were individually overexpressed in strain PCC 6803. The growth rate and pigment content (heme, phycocyanin, chlorophyll a and carotenoids) of 22 recombinant algal strains were characterized. Quantitative real-time PCR technology was used to investigate the molecular mechanisms underlying the changes in physiological indicators in the recombinant algal strains. Among the 22 mutant strains, the mutant overexpressing the haemoglobin gene (glbN) of strain PCC 6803 had the highest heme content, which was 2.5 times higher than the wild type; the mutant overexpressing the gene of strain PCC 7942 (hemF) had the highest phycocyanin content, which was 4.57 times higher than the wild type. Overall, the results suggest that genes in the porphyrin pathway could significantly affect the heme and phycocyanin content in strain PCC 6803. Our study provides novel crucial targets for promoting the accumulation of heme and phycocyanin in cyanobacteria.

Applications of the Whole-Cell System in the Efficient Biosynthesis of Heme

Heme has a variety of functions, from electronic reactions to binding gases, which makes it useful in medical treatments, dietary supplements, and food processing. In recent years, whole-cell system-based heme biosynthesis methods have been continuously explored and optimized as an alternative to the low-yield, lasting, and adverse ecological environment of chemical synthesis methods. This method relies on two biosynthetic pathways of microbial precursor 5-aminolevulinic acid (C4, C5) and three known downstream biosynthetic pathways of heme. This paper reviews the genetic and metabolic engineering strategies for heme production in recent years by optimizing culture conditions and techniques from different microorganisms. Specifically, we summarized and analyzed the possibility of using biosensors to explore new strategies for the biosynthesis of heme from the perspective of synthetic biology, providing a new direction for future exploration.

Systems metabolic engineering of Escherichia coli for hyper-production of 5‑aminolevulinic acid

BACKGROUND

5-Aminolevulinic acid (5-ALA) is a promising biostimulant, feed nutrient, and photodynamic drug with wide applications in modern agriculture and therapy. Although microbial production of 5-ALA has been improved realized by using metabolic engineering strategies during the past few years, there is still a gap between the present production level and the requirement of industrialization.

RESULTS

In this study, pathway, protein, and cellular engineering strategies were systematically employed to construct an industrially competitive 5-ALA producing Escherichia coli. Pathways involved in precursor supply and product degradation were regulated by gene overexpression and synthetic sRNA-based repression to channel metabolic flux to 5-ALA biosynthesis. 5-ALA synthase was rationally engineered to release the inhibition of heme and improve the catalytic activity. 5-ALA transport and antioxidant defense systems were targeted to enhance cellular tolerance to intra- and extra-cellular 5-ALA. The final engineered strain produced 30.7 g/L of 5-ALA in bioreactors with a productivity of 1.02 g/L/h and a yield of 0.532 mol/mol glucose, represent a new record of 5-ALA bioproduction.

CONCLUSIONS

An industrially competitive 5-ALA producing E. coli strain was constructed with the metabolic engineering strategies at multiple layers (protein, pathway, and cellular engineering), and the strategies here can be useful for developing industrial-strength strains for biomanufacturing.

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.

Efficient De Novo Biosynthesis of Heme by Membrane Engineering in Escherichia coli

Heme is of great significance in food nutrition and food coloring, and the successful launch of artificial meat has greatly improved the application of heme in meat products. The precursor of heme, 5-aminolevulinic acid (ALA), has a wide range of applications in the agricultural and medical fields, including in the treatment of corona virus disease 2019 (COVID-19). In this study, E. coli recombinants capable of heme production were developed by metabolic engineering and membrane engineering. Firstly, by optimizing the key genes of the heme synthesis pathway and the screening of hosts and plasmids, the recombinant strain EJM-pCD-AL produced 4.34 ± 0.02 mg/L heme. Then, the transport genes of heme precursors CysG, hemX and CyoE were knocked out, and the extracellular transport pathways of heme Dpp and Ccm were strengthened, obtaining the strain EJM-ΔCyoE-pCD-AL that produced 9.43 ± 0.03 mg/L heme. Finally, fed-batch fermentation was performed in a 3-L fermenter and reached 28.20 ± 0.77 mg/L heme and 303 ± 1.21 mg/L ALA. This study indicates that E. coli recombinant strains show a promising future in the field of heme and ALA production.

Construction of 5-aminolevulinic acid synthase variants by cysteine-targeted mutation to release heme inhibition

5-Aminolevulinic acid (5-ALA), a vital precursor for the biosynthesis of tetrapyrrole compounds, has been widely applied in agriculture and medicine, while extremely potential for the treatment of cancers, corona virus disease 2019 (COVID-19) and metabolic diseases in recent years. With the development of metabolic engineering and synthetic biology, the biosynthesis of 5-ALA has attracted increasing attention. 5-Aminolevulinic acid synthase (ALAS), the key enzyme for 5-ALA synthesis in the C4 pathway, is subject to stringent feedback inhibition by heme. In this work, cysteine-targeted mutation of ALAS was proposed to overcome this drawback. ALAS from Rhodopseudomonas palustris (RP-ALAS) and Rhodobacter capsulatus (RC-ALAS) were selected for mutation and eight variants were generated. Variants RP-C132A and RC-C201A increased enzyme activities and released hemin inhibition, respectively, maintaining 82.5% and 81.9% residual activities in the presence of 15 μM hemin. Moreover, the two variants exhibited higher stability than that of their corresponding wild-type enzymes. Corynebacterium glutamicum overexpressing RP-C132A and RC-C201A produced 14.0% and 21.6% higher titers of 5-ALA than the control, respectively. These results strongly suggested that variants RP-C132A and RC-C201A obtained by utilizing cysteine-targeted mutation strategy released hemin inhibition, broadening their applications in 5-ALA biosynthesis.

Recent advances in microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway

Tetrapyrroles are essential metabolic components produced by almost all organisms, and they participate in various fundamental biological processes. Tetrapyrroles are used as pharmaceuticals, food additives, and nutraceuticals, as well as in agricultural applications. However, their production is limited by their low extraction yields from natural resources and by the complex reaction steps involved in their chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, microbial cell factories were developed as an alternative method for tetrapyrrole production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway (e.g., 5-aminolevulinic acid, heme, bilins, chlorophyll, and vitamin B₁₂). Furthermore, outstanding challenges to the microbial production of tetrapyrrole compounds, as well as their possible solutions, are discussed.

Modular control of multiple pathways of Corynebacterium glutamicum for 5-aminolevulinic acid production

5-aminolevulinic acid (ALA) has broad potential applications in the medical, agricultural and food industries. Several strategies have been implemented successfully to try to improve ALA synthesis. Nonetheless, the low yield has got in the way of large-scale bio-manufacture of 5-ALA. In this study, we explored strain engineering strategies for high-level 5-ALA production in Corynebacterium glutamicum F343 using the C4 pathway. Initially, the glutamate dehydrogenase-encoding gene gdhA was deleted to reduce glutamate yield. Then the C4 pathway was introduced in the gdhA mutant strain F2-A (∆gdhA + hemA), resulting in a 5-ALA yield of up to 3.2 g/L. Furthermore, the accumulations of downstream metabolites such as heme, porphobilinogen, and protoporphyrin IX, were decreased. After evaluating the mechanisms of this synthetic pathway by RNA-Seq, the results showed that genes involved in both the C5 pathway and heme pathways were down-regulated in strain F2-A (∆gdhA + hemA). Interestingly, upstream genes of succinyl-CoA in the tricarboxylic acid (TCA) cycle, such as icd, lpdA, were up-regulated, while its downstream genes, including sucC, sucD, sdhB, sdhA, sdhCD, were down-regulated. These changes amplify the sources of succinyl-CoA and reduce its expenditure, before pulling the carbon flux to produce 5-ALA. Furthermore, the down-regulation of most genes of the heme pathway could reduce the drainage of 5-ALA, which further enhance its accumulation. To alleviate competition between glyoxylate and the TCA cycle, the isocitrate dehydrogenase-encoding gene aceA was also knocked out, resulting in 3.86 g/L of 5-ALA. Finally, the fermentation conditions were optimized, resulting in a maximum 5-ALA yield of 5.6 g/L. Overall, the blocking of the glutamate synthesis pathway could be a powerful strategy to re-allocate the carbon flux to produce 5-ALA. It could also enable the efficient synthesis of other TCA derivatives in C. glutamicum.

Metabolic engineering of microorganisms for the production of multifunctional non-protein amino acids: γ-aminobutyric acid and δ-aminolevulinic acid

Gamma-aminobutyric acid (GABA) and delta-aminolevulinic acid (ALA), playing important roles in agriculture, medicine and other fields, are multifunctional non-protein amino acids with similar and comparable properties and biosynthesis pathways. Recently, microbial synthesis has become an inevitable trend to produce GABA and ALA due to its green and sustainable characteristics. In addition, the development of metabolic engineering and synthetic biology has continuously accelerated and increased the GABA and ALA yield in microorganisms. Here, focusing on the current trends in metabolic engineering strategies for microbial synthesis of GABA and ALA, we analysed and compared the efficiency of various metabolic strategies in detail. Moreover, we provide the insights to meet challenges of realizing industrially competitive strains and highlight the future perspectives of GABA and ALA production.

Challenges and opportunities of bioprocessing 5-aminolevulinic acid using genetic and metabolic engineering: a critical review

5-Aminolevulinic acid (5-ALA), a non-proteinogenic five-carbon amino acid, has received intensive attentions in medicine due to its approval by the US Food and Drug Administration (FDA) for cancer diagnosis and treatment as photodynamic therapy. As chemical synthesis of 5-ALA performed low yield, complicated processes, and high cost, biosynthesis of 5-ALA via C4 (also called Shemin pathway) and C5 pathway related to heme biosynthesis in microorganism equipped more advantages. In C4 pathway, 5-ALA is derived from condensation of succinyl-CoA and glycine by 5-aminolevulic acid synthase (ALAS) with pyridoxal phosphate (PLP) as co-factor in one-step biotransformation. The C5 pathway involves three enzymes comprising glutamyl-tRNA synthetase (GltX), glutamyl-tRNA reductase (HemA), and glutamate-1-semialdehyde aminotransferase (HemL) from α-ketoglutarate in TCA cycle to 5-ALA and heme. In this review, we describe the recent results of 5-ALA production from different genes and microorganisms via genetic and metabolic engineering approaches. The regulation of different chassis is fine-tuned by applying synthetic biology and boosts 5-ALA production eventually. The purification process, challenges, and opportunities of 5-ALA for industrial applications are also summarized.

Recent advances in tuning the expression and regulation of genes for constructing microbial cell factories

To overcome environmental problems caused by the use of fossil resources, microbial cell factories have become a promising technique for the sustainable and eco-friendly development of valuable products from renewable resources. Constructing microbial cell factories with high titers, yields, and productivity requires a balance between growth and production; to this end, tuning gene expression and regulation is necessary to optimise and precisely control complicated metabolic fluxes. In this article, we review the current trends and advances in tuning gene expression and regulation and consider their engineering at each of the three stages of gene regulation: genomic, mRNA, and protein. In particular, the technological approaches utilised in a diverse range of genetic-engineering-based tools for the construction of microbial cell factories are reviewed and representative applications of these strategies are presented. Finally, the prospects for strategies and systems for tuning gene expression and regulation are discussed.

Downregulating of hemB via synthetic antisense RNAs for improving 5-aminolevulinic acid production in Escherichia coli

Aminolevulinic acid (ALA), a type of natural non-protein amino acid, is a key precursor for the biosynthesis of heme, and it has been broadly applied in medicine, agriculture. Several strategies have been applied to enhance ALA synthesis in bacteria. In the present study, we employed synthetic antisense RNAs (asRNAs) of hemB (encodes ALA dehydratase) to weaken metabolic flux of ALA to porphobilinogen (PBG), and investigated their effect on ALA accumulation. For this purpose, we designed and constructed vectors pET28a-hemA-asRNA and pRSFDuet-hemA-asRNA to simultaneously express 5-ALA synthase (ALAS, encoded by hemA) and PTasRNAs (2 inverted repeat DNA sequences sandwiched with the antisense sequence of hemB), selecting the region ranging from - 57 nt upstream to + 139 nt downstream of the start codon of hemB as a target. The qRT-PCR analysis showed that the mRNA levels of hemB were decreased above 50% of the control levels, suggesting that the anti-hemB asRNA was functioning appropriately. ALA accumulation in the hemB weakened strains were 17.6% higher than that obtained using the control strains while accumulating less PBG. These results indicated that asRNAs can be used as a tool for regulating ALA accumulation in E. coli.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02733-8.

CRISPR-Cas systems: Challenges and future prospects

The advancement gained over the past couple of decades in clustered regularly interspaced short palindromic repeats and CRISPR associated proteins (CRISPR-Cas) systems have revolutionized the field of synthetic biology, therapeutics, diagnostics and metabolic engineering. The technique has enabled the process of genome editing to be very precise, rapid, cost-effective and highly efficient which were the downfalls for the previously debuted zinc finger nucleases (ZFN) and transcription activator-like effector nucleases (TALEN) technologies. However, despite its great potential, challenges including off-target activity, method of delivery, ethical and regulatory issues still remain unresolved for the CRISPR-Cas systems. In this chapter, we present and point out the obstacles faced in implementation of the CRISPR-Cas system along with its future prospects.

Efficient solid-state fermentation for the production of 5-aminolevulinic acid enriched feed using recombinant Saccharomyces cerevisiae

Over the past decade, 5-aminolevulinic acid (5-ALA) has been highlighted as a promising functional feed additive and immunomodulator for improving the general health, immune response, and resistance to disease of livestock and poultry. However, it is very costly to produce 5-ALA using conventional chemical synthesis methods. Classical microbial fermentation fulfills the criteria of environmental friendliness, but the unsatisfactory titers still hinder actual industrial production. This study aimed to develop a solid-state fermentation (SSF) process that can be used to efficiently enrich feed with 5-ALA at a low cost. First, the endogenous 5-ALA synthase was overexpressed in Saccharomyces cerevisiae via integrating a copy of HEM1 gene into the chromosome and introducing a multi-copy plasmid pRS416-HEM1 which constitutively overexpresses HEM1 gene. The resulting strain ScA3 was able to produce 63.82 mg/L 5-ALA in shake-flask fermentation. After process optimization, a titer of 225.63 mg/kg dry materials, exceeding the usual effective dosage reported in animal trials, was achieved within 48 h through SSF of 20 kg feed in a 90-L steel drum. To our knowledge, this is the first report on combining microbial 5-ALA production with SSF in feed processing, which will hopefully promote the application and popularization of 5-ALA in the feed industry.

Two Completely Orthogonal Quorum Sensing Systems with Self-Produced Autoinducers Enable Automatic Delayed Cascade Control

The existence of crosstalk between quorum sensing systems limits their application in a complex environment. In this study, two completely orthogonal quorum sensing systems with self-produced autoinducers were built in one cell to enable the systems to be signal orthogonal and promoter orthogonal to each other. The systems were designed on the basis of the las system from Pseudomonas aeruginosa and the tra system from Agrobacterium tumefaciens. Both were optimized with respect to the orthogonality of signals and promoters by using a series of synthetic biology strategies and high-throughput screening. The systems were applied intracellularly, and an automatic delayed cascade circuit was successfully demonstrated, which can realize sequential gene expression without exogenous inducer. This circuit provides a new tool for biotechnological applications, such as metabolic regulation, that require sequential gene control. This cascade model expands the toolkit of synthetic biology research and indicates a high application potential of quorum sensing systems that are orthogonal to each other.

Strain engineering for high-level 5-aminolevulinic acid production in Escherichia coli

Herein, we report the development of a microbial bioprocess for high-level production of 5-aminolevulinic acid (5-ALA), a valuable non-proteinogenic amino acid with multiple applications in medical, agricultural, and food industries, using Escherichia coli as a cell factory. We first implemented the Shemin (i.e., C4) pathway for heterologous 5-ALA biosynthesis in E. coli. To reduce, but not to abolish, the carbon flux toward essential tetrapyrrole/porphyrin biosynthesis, we applied clustered regularly interspersed short palindromic repeats interference (CRISPRi) to repress hemB expression, leading to extracellular 5-ALA accumulation. We then applied metabolic engineering strategies to direct more dissimilated carbon flux toward the key precursor of succinyl-CoA for enhanced 5-ALA biosynthesis. Using these engineered E. coli strains for bioreactor cultivation, we successfully demonstrated high-level 5-ALA biosynthesis from glycerol (~30 g L^-1 ) under both microaerobic and aerobic conditions, achieving up to 5.95 g L^-1 (36.9% of the theoretical maximum yield) and 6.93 g L^-1 (50.9% of the theoretical maximum yield) 5-ALA, respectively. This study represents one of the most effective bio-based production of 5-ALA from a structurally unrelated carbon to date, highlighting the importance of integrated strain engineering and bioprocessing strategies to enhance bio-based production.

Enhanced 5-Aminolevulinic Acid Production by Co-expression of Codon-Optimized hemA Gene with Chaperone in Genetic Engineered Escherichia coli

5-Aminolevulinic acid (ALA) is an important metabolic intermediate compound with high value and has recently been used in agriculture and medicine. In this study, we have constructed six recombinant Escherichia coli (E. coli) strains that are involved in pET system under the regulation of the T7 promoter and LacI to express codon-optimized hemA gene from Rhodobacter capsulatus (RchemA) for ALA production via the C4 pathway. Due to codon optimization, hemA has a high transcriptional level; however, most RcHemA proteins were formed as inclusion body. To improve expression in soluble form, the vector with TrxA fusion tag was successfully used and co-expressed with partner GroELS as chaperone in another vector. As a result, ALA production increased significantly from 1.21 to 3.67 g/L. In addition, optimal ALA production was developed through adjustment of induction time and isopropyl β-D-1-thiogalactopyranoside (IPTG) concentration, as well as substrate addition conditions. By adopting a two-stage induction strategy, the highest ALA reached 5.66 g/L when 0.1 mM of IPTG was added at early exponential phase (i.e., OD₆₀₀ was equal to 0.7 to 0.8), while 6 g/L of glycine, 2 g/L of succinate, and 0.03 mM of pyridoxal 5'-phosphate (PLP) were provided in the mid-exponential phase in fermentation.